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Analysis of corrosion products in stress corrosion cracks Nikiforuk, Thomas Philip 1976

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ANALYSIS IN  OF CORROSION  STRESS  CORROSION  PRODUCTS CRACKS  by  THOMAS P H I L I P  B.A.-Sc.  University  NIKIFORUK  of British  C o l u m b i a , 1973  A T H E S I S SUBMITTED IN P A R T I A L FULFILMENT REQUIREMENTS MASTER  in  OF THE  FOR THE DEGREE OF  OF A P P L I E D  SCIENCE  the Department of METALLURGY  We a c c e p t required  this  thesis  as conforming  t o the  standard  THE UNIVERSITY  OF B R I T I S H  April,  COLUMBIA  1976  Thomas P h i l i p N i k i f o r u k , 1976  In  presenting  an  advanced  the I  Library  further  for  degree shall  agree  scholarly  by  his  of  this  written  this  thesis  in  at  University  the  make  that  it  purposes  for  freely  permission may  representatives. thesis  partial  for  It  financial  is  Date  J u l y 9th,  1976  by  gain  Columbia  for  the  understood  Metallurgy  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, Canada  British  extensive  be g r a n t e d  o of  of  available  permission.  Department  fulfilment of  shall  reference  Head  be  requirements  Columbia,  copying  that  not  the  of  copying  agree  and  of my  I  this  that  study. thesis  Department or  for  or  publication  allowed without  my  -  i -  ABSTRACT Circumferentially steel  were s t r e s s  yield  stress  of  under  and F e C l .  Alloy  3  of three  were a n a l y z e d  products  formed  by e l e c t r o n  of austenitic  f r e e l y corroding  types  conditions with  2  stainless  at t h e i r additions  30"4, 3 1 6 , a n d 310 w e r e  o f t h e i r known d i f f e r e n t s t r e s s  corrosion  types  MgCl2, and b o i l i n g M g C l  0  2  The  corroded  rods  i n b o i l i n g 154 C  HCl, CoCl ,  because  notched  chosen  corrosion s u s c e p t i b i l i t y .  on t h e s t r e s s  corrosion  d i f f r a c t i o n and e n e r g y  fracture  dispersive  surface  x-ray  analysis. Electron from  d i f f r a c t i o n of corrosion  the f r a c t u r e  in  a l l cases.  and  stripped  formed  on a l l a l l o y s was  and  chlorine.  the cracks  a corundum t y p e  was  could oxide.  felt  oxide  the v a r i a t i o n  E-pH  indicated  was  that  and  products,  the corrosion  traces  amounts  phosphorous  formed  predominantly  o f the s p i n e l oxide within  product  product  o f metal  oxide  in situ  lesser  magnesium,  s i m i l a r , being  stripped  a spinel  the corrosion  molybdenum,  equilibrium  i n s.c.c.  accounted  product  of corrosion  possible  The p r e s e n c e  anticipated  n o t be a d e q u a t e l y  a l l o y s was  s p i n e l with  oxide.  in situ  i n chromium and c o n t a i n e d  l e d to the conclusion  chromium e n r i c h e d  it  surface,  enriched  o f the various  with  analysis  iron, nickel, silicon,  Observations  consistent  x-ray  from t h e f r a c t u r e  the elements  or  showed t h e c o r r o s i o n  Qualitative  of  in  surface,  products, both  a •  chlorides was  the crack.  However,  b e h a v i o u r between t h e d i f f e r e n t  f o r i n terms o f the composition  alloys  of the  ACKNOWLEDGMENT I would l i k e t o thank Dr. D. Tromans f o r h i s a d v i c e , h e l p and understanding.  I would a l s o l i k e t o thank t h e f a c u l t y , s t a f f and f e l l o w  s t u d e n t s o f t h e Department o f M e t a l l u r g y f o r making my many y e a r s a t U.B.C. a l l w o r t h w h i l e .  Thanks i s a l s o due t o Ms L. F r e d e r i c k f o r  her h e l p and encouragement. F i n a n c i a l a s s i s t a n c e f o r t h i s t h e s i s was p r o v i d e d by M e a n I n d u s t r i e s L t d . and t h e Department o f M e t a l l u r g y a t U.B.C.  TABLE OF  CONTENTS  INTRODUCTION EXPERIMENTAL 2.1  General  2.2  Materials 2.2.1  Steels  2.2.2  Environments  2.3  Specimen P r e p a r a t i o n  2.4  Stress Corrosion  2.5  Corrosion  2.6  Electron Diffraction  2.7  X-ray  Tests  Product  Stripping  Spectroscopy  2.7.1  Introduct ion  2.7.2  X-ray  2.7.3  Mounting o f Thin Spectroscopy  2.7.4  Procedure  RESULTS AND  Spectroscopy  Films  f o r X-ray  Stress Corrosion Tests  3.2  S t r i p p i n g o f Oxides  Spectroscopy  3.2.1  Bromine-Methanol S t r i p p i n g  3.2.2  Acetate  Stripping  Electron Diffraction  Films  f o r S.E.M. X - r a y  OBSERVATIONS  3.1  3.3  o f Thin  - i v-  PAGE 3.4  3.5 4.  5.  X-ray S p e c t r o s c o p y  1+2  3.4.1  X-ray S p e c t r o s c o p y o f S t r i p p e d Oxides  42  3.4.2  In S i t u Spectroscopy  53  P a r t i a l Crack  55  DISCUSSION  60  4.1  D i f f r a c t i o n Studies  60  4.2  X-ray A n a l y s i s  62  4.3  P o t e n t i a l -pH E q u i l i b r i a W i t h i n t h e S.C.C. Crack  64  4.4  Growth o f Oxide F i l m s  68  4.5  E n v i s i o n e d Events W i t h i n t h e S t r e s s C o r r o s i o n Crack  70  4.6  E f f e c t o f A l l o y Composition  71  CONCLUSIONS  74  BIBLIOGRAPHY  75  APPENDIX A  78  APPENDIX B  139  -  LIST  V -  OF T A B L E S  TABLES I  PAGE Chemical A n a l y s i s o f C o r r o s i o n Product I s o l a t e d from S t r e s s C o r r o s i o n C r a c k s i n T y p e 316 S t a i n l e s s S t e e l , 14  from N i e l s e n . [14] II  Composition o f S t a i n l e s s S t e e l  12  III  A n n e a l i n g Data  12  IV  Stress  Corrosion  Test  Performed  15  V  Stress  Corrosion  Test  Results  28  VI  Summary  VII  d-Spacings and R e l a t i v e I n t e n s i t i e s f o r t h e S p i n e l s o f I r o n , F e 3 0 i t , Y F e 2 0 3 , F e C r 2 0 i + , f r o m ASTM X - r a y D i f f r a c t i o n Cards  35  VIII  D, a n d d - S p a c i n g s o f D i f f r a c t i o n  37  IX  D, d - S p a c i n g s , a n d R e l a t i v e p a t t e r n s Taken from Bromine ( s e e F i g . 8)  X  f o r Stainless Steel  of Electron Diffraction  Results  34  Patterns  Shown i n F i g . 7  V i s u a l I n t e n s i t i e s from S t r i p and A c e t a t e S t r i p  Diffraction Oxides 40  a Values C a l c u l a t e d from P l o t s o f D vs ( h + k + l )^ i n A p p e n d i x A, w h e r e S l o p e M = K / a , M D e t e r m i n e d f r o m Least Squares A n a l y s i s . A l l O x i d e s S t r i p p e d i n 1% B r o m i n e - M e t h a n o l S o l u t i o n E x c e p t Where N o t e d  43  XI  Summary  44  XII  X-ray I n t e n s i t i e s and d - S p a c i n g s f o r FesO^ and F e C l 2 ASTM I n d e x C a r d s #11-614 a n d 1-1106 R e s p e c t i v e l y  2  2  2  Q  Q  Al  Spectroscopy Results,  304 S.C.C. i n M g C l , Methanol S o l u t i o n 2  pattern A2  o f X-ray  Oxide  #22217  Stripped  See A p p e n d i x  w i t h 1%  B from  Bromine-  c a m e r a c o n s t a n t K = 1.88 i n s ' A °  304 S.C.C. i n M g C l 2 , O x i d e Methanol S o l u t i o n  S t r i p p e d w i t h 1%  pattern  c a m e r a c o n s t a n t K = 1.95 i n s « A °  #23299  52  79  Bromine81  - vi -  304 S.C.C. i n M g C l , Methanol S o l u t i o n 2  pattern  #23389  camera  304 S.C.C. i n M g C l Methanol S o l u t i o n pattern  2  2  2  2  2  #23434  2  #23436  #23580  2  #23579  2  + FeCl3,  #23333  2  K = 1.80  ins'A .  with  constant  1%  with  1%  1%  camera  Bromine-  with  •  ins*A° •  1% Bromineins'A  0  •  1% B r o m i n e -  K = 1.90  1%  0  1% Bromine-  K = 1.90  constant  Oxide S t r i p p e d with  Bromine-  K = 1.90  constant  constant  Bromine-  K = 1.91 i n s ' A  constant  with  0  K = 1.91 i n s * A ° •  constant  Oxide S t r i p p e d camera  316 S.C.C. i n M g C l , Methanol S o l u t i o n  Bromine  K = 1.91 i n s ' A ° •  Oxide S t r i p p e d  camera  Bromine-  1%  Oxide S t r i p p e d with  camera  #23581  #23329  + FeCl3,  with  Oxide S t r i p p e d with  camera  2  pattern  + FeCl3,  i n 1%  with  constant  + H C l , Oxide S t r i p p e d camera  2  constant  + H C l , Oxide S t r i p p e d  Bromine-  K = 1.84 i n s * A ° .  Oxide S t r i p p e d  camera  316 S.C.C. i n M g C l , Methanol S o l u t i o n pattern  constant  + H C l , Oxide S t r i p p e d  i n 1%  K = 1.84 i n s ' A ° .  Oxide S t r i p p e d  camera  304 S.C.C. i n M g C l Methanol S o l u t i o n pattern  2  #23452  304 S.C.C. i n M g C l Methanol S o l u t i o n pattern  constant  camera  304 S.C.C. i n M g C l Methanol S o l u t i o n pattern  + CoCl ,  #23464  304 S.C.C. i n MgC.l Methanol S o l u t i o n pattern  2  K = 1.88 i n s * A ° .  Oxide S t r i p p e d  camera  304 S.C.C. i n M g C l Methanol S o l u t i o n pattern  + CoCl ,  #23459  304 S.C.C. i n M g C l Methanol S o l u t i o n pattern  2  1% B r o m i n e -  constant  camera  304 S.C.C. i n M g C l Methanol S o l u t i o n pattern  + CoCl ,  #23462  304 S.C.C. i n M g C l Methanol S o l u t i o n pattern  Oxide S t r i p p e d w i t h  ins*A° •  BromineK = 1.93  ins*A° •  1% B r o m i n e -  constant  K = 1.92  ins*A° •  VI1 TABLES A15  A16  PAGE 316 S.C.C. i n M g C J , O x i d e Methanol S o l u t i o n  Stripped with  pattern  camera  2  316 S.C.C. i n M g C l Methanol S o l u t i o n pattern  A17  A19  A20  pattern A21  A22  A23  A26  + CoCl , 2  + CoCl  2  2  #23474  camera  #22205  camera  #22200  camera  camera  with  constant  Stripped with  pattern  camera  #23124  camera  1%  113  Brominei n s ' A . . . . 115 0  Bromineins-A°  117  Bromineins*A°  119  K = 1.91 i n s - A °  121  Bromine-  BromineK = 1.88  ins-A°  123  K = 1.88 i n s * A °  125  Bromine-  Cellulose  constant  310 S.C.C. i n MgCJ2 , O x i d e S t r i p p e d w i t h Acetate pattern  1%  1%  1%  K - 1.82  1%  constant  310 S.C.C. i n MgCfe , O x i d e Acetate #23146  with  constant with  1%  K = 1.80  constant  310 S.C.C. i n MgCl2 , O x i d e S t r i p p e d Methanol S o l u t i o n #22196  with  Stripped  with  Bromine-  K = 1.80  constant  Oxide S t r i p p e d  109  Bromine-  1%  with  constant  Oxide  Bromine-  K = 1.91 i n s . A °  , Oxide S t r i p p e d  + CoCl , 2  constant  Oxide S t r i p p e d  camera  1%  107  K = 1.91 i n s - A ° • • • • 111  Stripped with  310 S.C.C. i n MgCls , O x i d e S t r i p p e d Methanol S o l u t i o n  pattern A25  2  2  pattern A24  + H C l , Oxide  1%  K = 1.91 i n s . A °  constant  camera  310 S.C.C. i n M g C l , Methanol S o l u t i o n pattern  constant  camera  2  K = 1.91 i n s - A °  Stripped with  camera  2  Bromine-  + H C l , Oxide S t r i p p e d w i t h  #23472  316 S.C.C. . i n M g C l Methanol S o l u t i o n pattern  2  #23483  316 S.C.C. i n M g C l Methanol S o l u t i o n  constant  camera  #23404  316 S.C.C. i n M g C l Methanol S o l u t i o n pattern  + H C l , Oxide  #23407  316 S.C.C. i n M g C l Methanol S o l u t i o n pattern  2  #23406  316 S.C.C. i n M g C l Methanol S o l u t i o n pattern  A18  #22222  1%  K = 2.28 i n s - A  0  127  Cellulose  constant  K = 2.31 i n s » A °  129  - viii  -  £ j££  PAGE  c  A27  310 S.C.C. i n M g C l , Acetate 2  pattern A28  Oxide.Stripped with  #23043  310 S.C.C. i n M g C l  camera  2  Cellulose  constant  K = 2.28 i n s ' A  + H C l , Oxide S t r i p p e d w i t h  1%  0  • • • • 131  Bromine-  Methanol S o l u t i o n pattern A29  camera  constant  K = 1.91 i n s * A °  310 S.C.C. i n MgCl2 + H C l , O x i d e S t r i p p e d w i t h Methanol S o l u t i o n pattern  A30  #23418  #23417  310 S.C.C. i n M g C l Methanol S o l u t i o n pattern  #23488  camera  2  + CoCl ,0xide 2  camera  constant  Bromine-  K = 1.91 i n s « A ° - - - - 135  Stripped with constant  1%  133  1%  Bromine-  K = 1.85 i n s - A °  137  -  ix  -  L I S T OF FIGURES FIGURE 1  PAGE L a t t i c e parameter v a r i a t i o n with composition f o r N i , C r , Fe, s p i n e l s , from F r a n c i s [ 2 2 ]  2  S.C.C. C e l l  3  Schematic r e p r e s e n t a t i o n o f i n s i t u d i f f r a c t i o n o f surface oxide i n high r e s o l u t i o n d i f f r a c t i o n stage o f t h e T.E.M. T h e p r i m a r y e l e c t r o n beam s t r i k e s t h e surface  4  film  6  8  19  from from  c o n v e n t i o n a l specimen hollow graphite block  holder 25  29  Micrograph o f c o r r o s i o n product from f r a c t u r e s u r f a c e o f t y p e 310 s t a i n l e s s s t e e l s t r e s s c o r r o d e d i n b o i l i n g M g C l ^ solution. S t r i p p e d i n bromine-methanol s o l u t i o n 1200x)  31  Sample d i f f r a c t i o n p a t t e r n s f r o m s t r i p p e d s t r e s s c o r r o s i o n fracture surface oxides. a ) 304, b ) 3 1 6 , c ) 310 Diffraction  patterns taken  from  stress  corrosion  o x i d e s o f t y p e 310 s t r e s s c o r r o d e d a) bromine-methanol s t r i p b)  Diffraction specimens  cellulose  from  a)  type  b)  t y p e 304 i n M g C l pattern  304 i n M g C l  304 i n M g C l  36  fracture  i n MgCl2.  acetate s t r i p  p a t t e r n s taken  c) type 10  16  R e p r e s e n t a t i v e f r a c t o g r a p h s (40x m a g n i f i c a t i o n ) from stainless steels. a ) 3 0 4 , b ) 316, c ) 310  surface  9  long specimen i n p l a c e  and i s d i f f r a c t e d  (magnification 7  7 inch  Schematic diagrams o f b a c k s c a t t e r e d e l e c t r o n e f f e c t from specimen h o l d e r d u r i n g x-ray a n a l y s i s o f t h i n f i l m s . a) b)  5  with  8  39  exposed notch  2  + FeCl . M 0  4  2  + FeCl . M 0  3  2  + FeCl . M 0  4  3  3  3  3  2  3  areas o f  (spinel) pattern (rhombohedral) (spinel) pattern...  41  D i f f r a c t i o n p a t t e r n a n d x - r a y s p e c t r u m t a k e n f r o m t h e same a r e a on a f r a c t u r e : s u r f a c e o x i d e s t r i p p e d f r o m 3 1 6 - t y p e s p e c i m e n stress corroded i n MgCl + CoCl solution 46 2  spectrum  taken  from  2  11  X-ray  chromite  ore  47  12  X-ray s p e c t r a taken from t h e f r a c t u r e s u r f a c e oxide s t r i p p e d f r o m a t y p e 304 s p e c i m e n s t r e s s c o r r o d e d i n M g C l + FeCl solution. The t h r e e d i f f e r e n t s p e c t r a r e p r e s e n t t h e v a r i a t i o n i n i n t e g r a t e d CrKa/FeKa r a t i o o b s e r v e d f o r t h i s o x i d e . a ) C r K a / F e K a = 4.99/1 b ) C r K a / F e K a = 1.01/1 c ) C r K a / F e K a = 0.405/1 2  3  49  X-ray type  s p e c t r a taken 310  from  fracture  surface oxide  specimen s t r e s s  corroded  i n MgCl  a)  oxide  s t r i p p e d with bromine-methanol  b)  oxide  stripped with  cellulose  stripped  from  a  solution.  2  solution.  acetate  51  Comparison o f i n s i t u x-ray s p e c t r a from m e c h a n i c a l f r a c t u r e s u r f a c e s , with f r a c t u r e s u r f a c e s from specimens s . c . c . i n MgCl solution 2  a) a')  type type  304 304  mechanical f r a c t u r e s.c.c. c ) t y p e 310 c') t y p e 310  b ) t y p e 316 m e c h a n i c a l b') t y p e 316 s . c . c . mechanical fracture s.c.c  fracture  54  In s i t u x - r a y s p e c t r a t a k e n from f r a c t u r e s u r f a c e o x i d e o f t y p e 304 s p e c i m e n s . c . c . i n a M g C l + FeCl solution. Shows v a r i a t i o n i n x - r a y s p e c t r u m w i t h beam p e n e t r a t i o n ( a s i n d i c a t e d b y i n c r e a s i n g x-ray count r a t e ) a) CrKa/FeKa = .764/1 (100 counts/sec) b) CrKa/FeKa = 1.15/1 (300 counts/sec) 2  c) CrKa/FeKa  3  = 1.40/1 (900  counts/sec)  56  S o l i d i f i e d c r a c k s o l u t i o n on f r a c t u r e s u r f a c e o f t y p e 304 s p e c i m e n p a r t i a l l y stress corroded i n b o i l i n g MgCl s o l u t i o n and m e c h a n i c a l l y f r a c t u r e d a t room t e m p e r a t u r e (800x m a g n i f i c a t i o n ) 58 2  P o t e n t i a l -pH ( E - p H ) d i a g r a m f o r t h e C r - H 0 s y s t e m . o f s o l u b l e s p e c i e s 10 M. , f r o m B r o o k [33] 2  6  P o t e n t i a l -pH Concentration  (E-pH) d i a g r a m f o r t h e Ni-H20 s y s t e m . o f s o l u b l e s p e c i e s 10 M., from Brook  P o t e n t i a l -pH Unit a c t i v i t y  ( E - p H ) d i a g r a m f o r t h e Fe--H 0 s y s t e m o f s o l u b l e s p e c i e s , from B i e r n a t and  6  2  Concentration 65  [33]  65  a t 150°C. Robins[31]...  66  C a l c u l a t e d a r e a s o f s t a b i l i t y o f F e , F e C l 2 * 4 H 2 0 , a n d Fe30i+ i n t h e presence of a s o l u t i o n e l e c t r o n e u t r a l i n F e C l 2 , (schematic) from Pourbaix [5] 66 Schematic  Evans diagram  showing p o s s i b l e  electrochemical behaviour. zation  behaviour  Base a l l o y  d e p i c t e d by  curves  effects  has  a and  of a l l o y i n g  on  electrochemical polaric.  Upon a l l o y i n g  with  n i c k e l , t h e a l l o y r e v e r s i b l e p o t e n t i a l i n c r e a s e s from E t o E^, r e s u l t i n g i n a lower c o r r o s i o n c u r r e n t I to I' . Alloying corr corr may a l s o l o w e r t h e e x c h a n g e c u r r e n t d e n s i t y f o r h y d r o g e n r e d u c t i o n f r o m I_ t o I ' , a g a i n , l o w e r i n g I to I' [39] 73 corr corr \, P l o t o f D vs ( h + k + l ) from Table A l . Diffraction pattern #22217, 304 s . c . c . i n M g C l 2 , o x i d e s t r i p p e d w i t h 1% b r o m i n e methanol s o l u t i o n 80 c  0  0  2  Plot  o f D vs  pattern  (h  2  2  + k  #23299, 304  2  2  + l  2  s.c.c.  2  )  2  from  Table  A2.  i n MgCl2, o x i d e  Diffraction stripped  with  1%  bromine-methanol s o l u t i o n  82  P l o t o f D vs ( h + k + l ) ^ f r o m T a b l e A3. Diffraction p a t t e r n #23389, 304 s . c . c . i n M g C l , o x i d e s t r i p p e d w i t h bromine-methanol s o l u t i o n 2  2  2  2  1% 84  - xi -  FIGURE A4  PAGE Plot  of D vs ( h  2  + k  2  + l  ) ^ from Table  2  p a t t e r n #23462, 3 0 4 ' s . c . c . i n M g C l 1% b r o m i n e - m e t h a n o l s o l u t i o n . A5  Plot  of D vs ( h  2  + k  2  + l ^ f r o m  2  T a b l e A5.  stripped  with  2  Diffraction  + CoCl , 2  oxide  stripped 88  P l o t o f D v s ( h + k + I ) * f r o m T a b l e A6. Diffraction p a t t e r n #23464, 304 s . c . c . i n M g C l + C o C l , o x i d e s t r i p p e d w i t h 1% b r o m i n e - m e t h a n o l s o l u t i o n .  90  P l o t o f D vs ( h + k + l ) ^ f r o m T a b l e A7. Diffraction p a t t e r n #23452, 304 s . c . c . i n M g C l + HCl, oxide stripped w i t h 1% b r o m i n e - m e t h a n o l s o l u t i o n  92  Plot of D vs ( h + k + l ) * f r o m T a b l e A8. Diffraction p a t t e r n #23434, 304 s . c . c . i n M g C l + HCl, oxide stripped w i t h 1% b r o m i n e - m e t h a n o l s o l u t i o n  94  P l o t o f D vs ( h + k + l ) ^ f r o m T a b l e A9. Diffraction p a t t e r n #23436, 304 s . c . c . i n M g C l + HCl, oxide stripped w i t h 1% b r o m i n e - m e t h a n o l s o l u t i o n  96  Plot of D v s . ( h + k + l ) f r o m T a b l e A10. Diffraction p a t t e r n #23580, 304 s . c . c . i n M g C l + FeCl3, oxide stripped w i t h 1% b r o m i n e - m e t h a n o l s o l u t i o n  98  2  2  2  5  2  A7  Diffraction  2  86  p a t t e r n #23459, 304 s . c . c . i n M g C l w i t h 1% b r o m i n e - m e t h a n o l s o l u t i o n A6  A4.  + "C6C1 ' o x i d e  2  2  2  2  2  A8  2  2  2  5  2  A9  2  2  2  2  A10  2  2  2  i  2  2  All  Plot  of D vs ( h  2  + k  2  + l )* 2  5  from Table  All.  Diffraction  p a t t e r n #23579, 304 s . c . c . i n M g C l 2 + F e C l 3 , o x i d e w i t h 1% b r o m i n e - m e t h a n o l s o l u t i o n . A12  Plot  of D vs ( h  2  + k  Diffraction pattern oxide stripped with A13  A14  2  + l ^ f r o m  Table  A12.  #23581, 304 s . c . c . i n M g C l + 1% b r o m i n e - m e t h a n o l s o l u t i o n . 2  P l o t of D vs ( h + k + l ) ^ f r o m T a b l e A13. D i f f r a c t i o n p a t t e r n #23333, 316 s . c . c . i n MgClo, o x i d e s t r i p p e d w i t h 1% b r o m i n e methanol s o l u t i o n 2  2  2  2  FeCl , 3  -^2  2  P l o t o f D vs ( h + k + l ) ^ f r o m T a b l e A14. D i f f r a c t i o n p a t t e r n #23329, 316 s . c . c . i n M g C l , o x i d e s t r i p p e d w i t h .1% b r o m i n e methanol s o l u t i o n . 2  stripped  2  ±  - x i iFIGURE A15  PAGE P l o t o f D vs C h " + k + l ) ^ f r o m T a b l e A15. D i f f r a c t i o n p a t t e r n #22222, 316 s . c . c . i n M g C l s o x i d e s t r i p p e d w i t h .1% b r o m i n e methanol s o l u t i o n  108  Plot o f D vs ( h + k + l ) ^ f r o m T a b l e A16 D i f f r a c t i o n p a t t e r n #23406, 316 s . c . c . i n M g C l 2 + H C l , o x i d e s t r i p p e d w i t h .1% b r o m i n e methanol s o l u t i o n  110  P l o t o f D vs ( h + k + l ) " " f r o m T a b l e A17. D i f f r a c t i o n p a t t e r n #23407, 316 s . c . c . i n M g C l 2 + H C l , o x i d e s t r i p p e d w i t h 1% b r o m i n e methanol s o l u t i o n  112  Plot o f D vs ( h + k + l ) ^ f r o m T a b l e A18. D i f f r a c t i o n p a t t e r n #23404, 316 s . c . c . i n M g C l 2 + H C l , o x i d e s t r i p p e d w i t h 1% b r o m i n e methanol s o l u t i o n  114  2  2  2  2  A16  A17  A18  A19  A20  A21  A22  A23  A24  2  2  2  2  2  2  2  2  2  2  Plot of D vs.(h + k + l ) ' f r o m T a b l e A19. D i f f r a c t i o n p a t t e r n #23483, 316 s . c . c . i n M g C l 2 + C 0 C I 2 , o x i d e s t r i p p e d w i t h 1% b r o m i n e methanol s o l u t i o n 2  2  2  1  '.  116  Plot of D vs ( h + k + l ) ^ f r o m T a b l e A20. D i f f r a c t i o n p a t t e r n #23472, 316 s . c . c . i n M g C l 2 + C 0 C I 2 , o x i d e s t r i p p e d w i t h 1% b r o m i n e methanol s o l u t i o n  118  P l o t o f D vs ( h + k + l ) ' f r o m T a b l e A21. D i f f r a c t i o n p a t t e r n #2347^, 316 s . c . c . i n M g C l 2 + C 0 C I 2 , o x i d e s t r i p p e d w i t h 1% b r o m i n e methanol s o l u t i o n  120  Plot of D vs ( h + k + l )^ f r o m T a b l e A22. D i f f r a c t i o n p a t t e r n #22205, 310 s . c . c . i n M g C l 2 , o x i d e s t r i p p e d w i t h 1% b r o m i n e - m e t h a n o l solution.  122  Plot o f D vs ( h + k + l )^ f r o m T a b l e A23. D i f f r a c t i o n p a t t e r n #22200, 310 s . c . c . i n M g C l 2 , o x i d e , s t r i p p e d w i t h 1% b r o m i n e methanol s o l u t i o n  124  P l o t o f D vs ( h + k + l ) ^ f r o m T a b l e A24. D i f f r a c t i o n p a t t e r n #22146, 310 s . c . c . i n M g C l 2 , o x i d e s t r i p p e d w i t h 1% b r o m i n e - m e t h a n o l s o l u t i o n  126  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2  - xiii  -  FIGURE A25  PAGE Plot  o f D vs ( h  Diffraction MgCl , 2  A26  2  + I ) ' from 2  5  p a t t e r n #23146,  oxide  stripped with  T a b l e A25.  310 s . c . c . i n cellulose  acetate  128  2  2  oxide  stripped with  2  2  cellulose  acetate  130  2 !^  P l o t o f D v s (h + k + 1 ) from T a b l e A27. • D i f f r a c t i o n p a t t e r n #23043, 310 s . c . c . i n MgCl ,  oxide  2  acetate  132  P l o t o f D vs (h + k + 1 ) f r o m T a b l e A28. D i f f r a c t i o n p a t t e r n #23418, 310 s . c . c . i n MgCl + H C l , o x i d e s t r i p p e d w i t h 1% b r o m i n e methanol s o l u t i o n  134  P l o t o f D vs ( h + k + l ) ^ f r o m T a b l e A29. D i f f r a c t i o n p a t t e r n #23417, 310 s . c . c . i n MgCl + H C l , o x i d e s t r i p p e d w i t h 1% b r o m i n e methanol s o l u t i o n  136  2  A28  + k  2 2 2 3" P l o t o f D v s (h + k +1 ) f r o m T a b l e A26. D i f f r a c t i o n p a t t e r n #23124, 310 s . c . c . i n MgCl ,  A27  2  stripped with  2  , 2  cellulose  2,  h  2  A29  2  2  2  2  2 A30  2 !" 2  2  Bl  2  P l o t o f D v s (h + k + 1 ) f r o m T a b l e A30. D i f f r a c t i o n p a t t e r n #23488, 310 s . c . c . i n ' MgCl + C o C l , o x i d e s t r i p p e d w i t h 1% b r o m i n e methanol s o l u t i o n 2  S.E.M. x - r a y of type  spectrum  304 s t r e s s  from  corroded  fracture  S.E.M. x - r a y  spectrum  from  oxide  i n MgC.l2 s o l u t i o n .  S t r i p p e d with bromine-methanol B2  surface  solution.  fracture  140  surface  oxide  o f t y p e 304 s t r e s s c o r r o d e d i n M g C l 2 + H C l s o l u t i o n . S t r i p p e d with bromine-methanol s o l u t i o n B3  S.E.M. x - r a y of type  solution. B4  spectrum  304 s t r e s s  from  corroded  138  fracture i n MgCl2  surface +  141  oxide  C0CI2  S t r i p p e d w i t h bromine-methanol  solution  S.E.M. x - r a y s p e c t r u m f r o m f r a c t u r e s u r f a c e o x i d e o f t y p e 316 s t r e s s c o r r o d e d i n M g C l 2 s o l u t i o n . Stripped with bromine-methanol s o l u t i o n .  142  143  -  xiv -  FIGURE B5  B6  PAGE S.E.M. x - r a y s p e c t r u m f r o m f r a c t u r e s u r f a c e o x i d e o f t y p e 3 1 6 . s t r e s s c o r r o d e d i n MgCl2 + H C l s o l u t i o n . Stripped with bromine-methanol s o l u t i o n S.E.M. x - r a y type  Stripped B7  B8  spectrum  316 s t r e s s  from  corroded  fracture  i n MgCl2  surface  + C0CI2  144  o f oxide o f solution.  with bromine-methanol s o l u t i o n  S.E.M. x - r a y s p e c t r u m f r o m f r a c t u r e s u r f a c e t y p e 310 s t r e s s c o r r o d e d i n M g C l 2 s o l u t i o n . with bromine-methanol s o l u t i o n  14 5 oxide o f Stripped 146  S.E.M. x - r a y s p e c t r u m f r o m f r a c t u r e s u r f a c e o x i d e o f t y p e 310 s t r e s s c o r r o d e d i n M g C l + HCl solution. Stripped with bromine-methanol s o l u t i o n  147  S.E.M. x - r a y s p e c t r u m f r o m f r a c t u r e s u r f a c e o x i d e o f t y p e 310 s t r e s s c o r r o d e d I n M g C l 2 + C 0 C I 2 s o l u t i o n . Stripped w i t h bromine-methanol s o l u t i o n  148  2  B9  -  1. Austenitic corrosion  Such e n v i r o n m e n t s  of  MgCl .  justified  studied  occur  studies  fracture surfaces  s.c.c.  film, film  dissolution.  and prevent  crack  may  a c t as a l o c a l  electrochemical  cathode  of corrosion  film  has  t o aqueous  i s considered on c r a c k  o f the crack  product  been  on  s.c.c. necessary  geometry lateral  a passive walls.  t i pundergoing [3].  solutions  products  f i l m s may r e s t r i c t  geometry  o f the corrosion  aqueous  The  type corrosion  anodic d i s s o l u t i o n ,  The m e c h a n i c a l and a t the crack  as i s p r o p o s e d by f i l m  t i p may  rupture/slip  d i s s o l u t i o n models [ 4 ] . [5]  Pourbaix aqueous  of  properties  and crack  chloride  on t h e s u b j e c t ,  by e i t h e r forming  t o a crack  the c o n t r o l l i n g factor i n s . c . c ,  step  and  blunting,  o r b y means o f n o b l e m e t a l e n r i c h m e n t  d e p e n d i n g on t h e e n v i r o n m e n t  be  The c o r r o s i o n  solutions.  industrial  papers  relation  of reaction  where  solutions  [ 1 ] , [2] process because o f i t s i n f l u e n c e  and/or l o c a l i z e d dissolution  industry  good c o r r e l a t i o n w i t h  and t h e i r  chloride  boiling  2  the. many p u b l i s h e d  I n many s i t u a t i o n s some t y p e for  by u t i l i s i n g  c o n d u c t e d on t h e n a t u r e  to stress  and t h e problem has been  testing of steels i n MgCl  However, d e s p i t e  corrosion  o f h o t aqueous  present,  i n the laboratory  have been  susceptible  i n the chemical  are usually  because o f t h e g e n e r a l l y  performance.  stress  i n the presence  frequently,  The f r e q u e n t  2  few  (s.c.c.)  o r contaminants  extensively  INTRODUCTION  stainless steels are notoriously  cracking  residuals  1 -  the electrochemical  c h l o r i d e environments with r e s t r i c t e d  cracks.  He c o n c l u d e s  iron should  solution  has s t u d i e d  occur with  saturated  i n both  that  i n s i d e these  the evolution FeCl '4H 0 2  2  aspects  of corrosion i n  geometry; p i t s ,  occluded  o f hydrogen  and FesO^.  cells i n an  crevices,  the corrosion acidified  Latanision  and  Staehle  -  2  -  [4]proposed  a mechanism where t h e  s i d e s of the  in  element  (nickel  the noble  s t e e l ) thus of this  o c c u r r i n g has  of the films and  been  stainless  cracking occurs  passive  films,  [3].  Slip  dissolution  rupture  d e p e n d on  the  mechanical  and  they  For  will  example,  crack  r a t e o f r e p a s s i v a t i o n may Hydrogen  and  tip.  deformation  be  s t e e l may  Evidence  steels models  [6]  and  [7],  reformation  s t u d i e s on  i n tension at strains then  stainless  of  electrochemical properties  a major  c r a c k i n g models f o r s . c . c . Corroding  crack  enriched  o f 0.05  factor  indirectly  hydrolyse  magnetite -  0.08%,  i n s.c.c. d e p e n d on  according  of the  to;  9-11] +  + 4 H  2  i n aqueous M g C l  reduced  according  hydrogen  to  i n the  occur  austenite  by  in nickel chloride  0 ^  Fe 0 3  + e  H  lattice  either  cleavage  4  ions are  may  [12] ahead o f the  , and ad  +  8 H  diffuse  precipitate  p a r t i n g of the enrichment  +  2e~  into  i n voids  crack; propagation  or p r e f e r e n t i a l  S t r e s s s o r p t i o n models  the  +  (l)  produced which are  o f c h l o r i d e ions onto defect s i t e s  t i p , lowering  physical  +  interfaces.  adsorption  2  hydrogen  2  to H  metal  ation martensite  crack  steel  of  stainless  continuous  3 F e  then  for ferritic  become  case  respect to the  the  corrosion products.  Thus,  i n the  by  [8] indicate  steels.  C3,  with  found  corrosion product.  the  alloy,  becoming i n a c t i v e  304L a u s t e n i t i c where  of the  crack  cathodically  the  metal.  or  induce  of the  dissolution f o r s.c.c.  The deform-  crack  along  martensite  require  s u r f a c e energy  of the  surface  A c o r r o s i o n r e a c t i o n which  of the  [13].  surface w i l l  the  at the p l a s t i c a l l y lattice  and  strongly affect  could  deforming  resulting  the  in a  results  adsorption  ions.  Nielsen  [14]  s t u d i e d the  role  of  corrosion products  i n s.c.c.  crack  of  -  propagation and  of austenitic  concluded  together with He  isolated  surrounding  metal  methanol. thick.  noted  M 0 3  t h a t the  giving  distinct  a  the  was  fans  p a t t e r n . T h i s was  analysis,  see. T a b l e  corrosion product,  The  series  corrosion  products  c r a c k t i p and builds  up  occurs.  regions,  In  i n chromium and e n v i s i o n e d by  crack  and the  solution,  occur.  away f r o m  is  the  as  primarily  M2O3.  He  as  into  electron area of  Chemical  the  follows: the  that crack  the  enlarged  The  soluble metal  crack  t i p towards  would transform  also  a loss  electron  advancing  metal  material  propagation crack ions  the  and  migrate  cathodic  hydroxides.  to hydrated  metal  repeated.  o f r e c e n t work by  Smith e t  was  The  precipitated  ions to p r e c i p i t a t e  the hydroxide  the process light  i s drawn  anodes  reacting with hydroxide  a level  in  angstroms  corrosion product  distance behind o f the  the  i n nickel..  N i e l s e n was  t o such  environment  field  a  together with  deficient  deposited a f i n i t e  w i t h i n the  chloride  hundred  to a microporous  t h a t the  subsequent wedging a c t i o n  electrical  the hot  oxides  are  corrosion of local  under the  In  the  stress The  further  of events  few  subsequent r e c r y s t a l l i z a t i o n .  studies l e d N i e l s e n to conclude enriched  a  interpreted  with  oxide  dissolving  indicated  convert  to heating e f f e c t s ,  a hydrated  s.c.c.  underwent a t r a n s f o r m a t i o n i n the  "amorphous" a r e a would  of the  which,  volume o f b r o m i n e  t r a c e s o f a rhombohedral oxide  w a t e r due  diffraction  action,  c o r r o s i o n c r a c k by  p a t t e r n s o f the  crystalline  solutions  2  enough t o t r i g g e r  " f a n shaped" c o r r o s i o n products  1,  MgCl  t o e x e r t a wedging  stress  corrosion product  initially  was  in boiling  i n a s o l u t i o n c o n t a i n i n g 5% b y  diffraction  beam; an  steels  applied stress  structure with  tt  effect  from  matrix  This l e f t  Electron  spinel  and  the product  -  stainless  t h e i r primary residual  3  al.[9],  Baker e t  al.[15],  - 4  Table  I.  -  Chemical A n a l y s i s of Corrosion Product I s o l a t e d from S t r e s s C o r r o s i o n C r a c k s i n T y p e 316 S t a i n l e s s S t e e l , from N i e l s e n [14]  Element  wt  %  Oxide  wt  %  1 i  j  |  C r  21.12  Cr 0  3  30.9  Fe  13.23  Fe 0  3  18.9  Ni  1.85  NiO  2.36  1.95  Mo 03  1.49  Mo  i  Mg  -  Si  -  2  2  2  •  -  MgO Si0  2  -  Brown  [ 1 1 ] , and  solution  at the  hydroxides a spinel  film  on  necessary  and  Hochman  t i p t o be exist.  iron  has  of the  been  f o r s.c.c.  Staehle  [7] i n d i c a t e  iron w i l l  slip  emergence a t t h e  step  al.[15],  stress  2  a boiling  f o r m e d on  %  i n both  304  o f the 1-2  cases.  of the bulk  1.2  -  thin  c r a c k s was surfaces  an  25  i n solutions  solution  the  o f the  same p'H.  i n crack  formation, and  steel  and  found the  go  the is  al.[l5]  This  film  will  was  was  films  of  between  o f the  67  wt  %  film  1.2  and  However c r a c k i n g advancing  i n the  crack  range  of  stress corrosion  t h a t f o r m e d on was  determine  a poor the  the  exterior  electrical  role  of  film  o r g a n i c compounds w e r e a d d e d  in  order  chromium i o n s t h u s  by  Baker  corrosion  always  i n the  ruptured  maintained  formed.  pH  be  cycle.  water  shown  solution  in turn w i l l  pH  iron  have  into  in a solution  This f i l m To  Baker e t  r e p e a t i n g the  t h a t the pH  same a s  deposition  iron  film.  vt % d i s t i l l e d  found  chromium e n r i c h e d s p i n e l .  complex the  of  that  significant,  h i s co-workers  a non-protective film  corrosion film  a s s u m e d t o be  that  observation  o f a chromium and  that a protective  conducting  to  oxide  s a m p l e when t h e  I t was  independent The  being  preferentially  stainless  2  was  2.5.  presence  crack t i p thus  3  w h e r e a s , b e l o w pH  occurred  form  F e C l - 6 H 0 and  exterior  chloride  i t is felt  the  s t u d i e s by  S t a e h l e and  p o i n t o f 125°C, found  the  1-3,  hot  others, i t i s f e l t  c o r r o s i o n crack t i p , which  working with  M g C l - 6 H 2 0 , 8 wt  2.5,  the  that nickel w i l l  the  at  [17], i n d i r e c t  s.c.c. c o r r o s i o n product.  c h r o m i u m and  by  the  propagation.  work b y  alloys,  a pH  corrosion products, while  passivate  et  observed  Birley  Fe-Cr-Ni  indicate  F u r t h e r more, a l t h o u g h  work b y  while  [16] which  acidic with  Direct  spinel for  crack  could not  wedging a c t i o n not  Marek and  5 -  preventing film  formation.  -  General  corrosion  developed  on  the  concluded that film  was  film  -  observed but  specimen s u r f a c e  a  critical  were n e c e s s a r y  oxide  6  pH  produced  confines  precipitate  and  and  f o r s.c.c.  no  no  the  pH  protective  film  c r a c k s were o b s e r v e d .  a protective The  or  poor e l e c t r i c a l  i s m a i n t a i n e d by  electrochemical  cell  Baker et  al.  conducting  hydrolysis  reaction  to  and the  the crack  tip. Birley and  310  aqueous  [17]  stainless  steels  solutions,  found  corrosion  primarily  45  wt  % MgCl  a  spinel.  i n the  however, were t h i c k primarily  of  in MgCl  possible  enough t o  3  perform  solutions  was  an  Hochman [ 1 8 ]  the  a  chromium e n r i c h e d ,  s.c.c.  fracture  surface  of  h a v e shown t h a t  stainless  steels  conducted  controlled  exposed  to  a passive  formed  to  thinness  the  (the  same a s  nickel.  He  iron enriched  304L FeCl3  crack  to  in boiling of  the  oxide.  Baker et the  al.'[15])  oxides  concluded  potential,  work o f  film  corrosion  the  s p i n e l with  single wt  energy  were oxide traces  crystals of  % MgCl  does  and  previous  film  dispersive  nickel deficient,  exist  on  the  corrosion  316  solutions.  2  Davis  surface  Wilde  [20]  polarization studies  i n b o i l i n g MgCl2 and  showed a c h r o m i u m e n r i c h e d the  in situ  b o i l i n g MgCl2 s o l u t i o n s .  austenitic stainless steels  Despite  s.c.c.  oxides  i r o n and  Wilde  which  due  h a v e o b s e r v e d by  s t a i n l e s s s t e e l i n b o i l i n g 45  304  of  i n the  on  MgCl2 +  chemical analysis;  austenitic [19]  % MgCl2 and  solutions  2  studies  oxychlorides.  analysis, on  not  FeCl3 + MgCl  + FeCl  2  Marek and  product  was  wt  product  i r o n , chromium, magnesium, and  magnesium  x-ray  the  i n 45  Chemical analysis  solutions  2  formed  formed  chemical analysis  austenitic  be  Oxides  i n d i f f r a c t i o n and  i s f o r m e d on  authors which  LiCl  the  support  2  of  has on  solutions  steel the  and  surface. presence  of  -  an  iron  no  study  steel The  and  on  chromium c o n t a i n i n g  has  been p e r f o r m e d on  the  s t r u c t u r e and  i n hot  initial in  s p i n e l i n the the  a l l three,  composition  The  product  varies  likewise.  2  cubic  s t r u c t u r e , with  ions' i n the  + 3  and  + 2  the  16  (Fe  ions  + 2  sites.  by  a  Addit ions  the  chromite.  change  has  a higher  and  ferrous Nickel  NiCr20i , +  of  of  The  in lattice  will  + 3  change from parameter  c o n d u c t i v i t y than ions and  i n the  NiFe20i , t  MnFe 0i . 2  t  prefer to  ions  A  a  convert  solid  sites form  the  due  face and  the  in  centred the  32  oxygen,  spinel, ferrous  the  inverse  spinel  Fe-^gCr-]^  +  to  2  0^  F e 2 ( C r 3 ) 0^ , +  conductivity. presence  Fe 2  tetrahedral  to normal s p i n e l i s  to  s.c.c.  The  stoichiometric oxide,  and  the  situate in  replace to  vary  changes  atoms;  approximately  F i g . 1)  chromite  also  will +  at  56  inverse  move F e 2  inverse  (see  octahedral  manganese can  to  in a  ions  occurring lead  arranged  i s an  of  nickel.  M2  and  +  lattice  tetrahedral sites  +  constant  structure  has  chromium w i l l  transition Cr  Cr 3  at  molybdenum c o n t e n t  cell  chromium  with  and  unit  structure  of  sites  additions  additions  known as  The  the  a normal s p i n e l , Further  sites.  thus  .  temperature  ions  i n the  sites,  1 +  failure  have v a r y i n g  chromium and  0~2  s p i n e l s , the  octahedral  Large  ions  + 2  310  the  iron  +  i n the  M  the  in stainless product.  have s t u d i e d of  crack,  stress corrosion  or  In  +3  Fe 3)0  the  octahedral  M .  octahedral  + 3  [22]  has  4  and  elements  composition  s p i n e l s r e s u l t i n g from a d d i t i o n s +  alloy  chromium, and  known i f t h e  +  stress corrosion  of the 316  its not  Francis  of  constant  nickel,  normal s p i n e l ( M 2 ) ( M 3 ) 0  8 M  304,  but  Francombe[21] and iron  effect  c h l o r i d e s o l u t i o n s at  stress level.  corrosion  Fe  -  austenitic stainless steels,  times  M  7  +  accompanied Magnetite  of both  ferric  [37]. spinels with  iron  and  chromium;  s o l u t i o n o f mixed s p i n e l phases  may  -  !  Fig.  1.  Lattice  3°'  P'CrzO!  8 -  NiCrzOi  parameter v a r i a t i o n  from Francis  [22].  with  NiF;,O  t  Fe,Oi  composition  f o r N i , C r , Fe  spinels,  - 9-  occur  s i n c e a l l types  [22].  Any m i x t u r e  of iron-containing  of spinels  parameter o f t h e e n t i r e solely a  by e l e c t r o n  chemical  phases  t o be performed  stripped  and x-ray from  [14,15,17,23]. and  i n a variation  spinel  diffraction.  are completely  phases  cannot  be  the spinel  studies o f oxide  identified  phase o r  to thin  electron  and t h i c k  i n a variety  diffraction  oxides.  o f ways.  attachment  mounted on a s c a n n i n g  qualitative  electron analysis  microscope  W i t h S.E.M. c a p a b i l i t i e s t o approximately  if  t h e r e a r e any major c o m p o s i t i o n For t h e present  austenitic  stainless  variations  c o n t a i n i n g 45 wt % o f M g C l  composition then  o f the resulting  determined.  the b a s i c  MgCl  were a l s o  partially  2  z  yield  Additions o f HCl,  solution  t o determine  cracked  stress  product FeCl3  their  i n an attempt  analyzer  number 1 1 .  selected  i tpossible  to  areas determine  i n the oxide.  (b.p.154°C).  corrosion  x-ray  a quick  rods  304, 3 1 6 , a n d 310 w e r e s t r e s s  corroding conditions at their  solution  t o analyze  c i r c u m f e r e n t i a l l y notched  steels,  o f oxides  (S.E.M.) a n d a  above sodium, atomic  60,000x m a g n i f i c a t i o n , m a k i n g  study  analysis  This allows  i ti s also possible  up  authors  and convenient  dispersive  microscope  (T.E.M.).  f o r a l l elements  i s easy  in situ  I n t h e p r e s e n t work, t h e most  a n d q u i c k e s t was b y means o f a n e n e r g y electron  both  by s e v e r a l  Chemical  convenient  transmission  films,  t h e s u b s t r a t e , have been performed  can be a c c o m p l i s h e d  was  of lattice  Therefore, i t i s necessary f o r  to identify  diffraction  Transmission  i s applicable  freely  miscible  present.  Electron and  result  oxide, thus  o r x-ray  analysis  will  spinels  o f three corroded  i n a boiling  aqueous  The s t r u c t u r e a n d  on t h e f r a c t u r e and C o C l  effect  under  2  surface  w e r e made t o  on t h e o x i d e .  t o examine t h e s o l u t i o n  Specimens inside  - 10 -  the stress corrosion crack. In order to understand the mechanism of s . c . c , maximum information is required regarding the phases present at the crack t i p . This studywas an attempt to provide further information on the crack t i p chemistry.  -  2. 2.1  11 -  EXPERIMENTAL  General T h r e e a u s t e n i t i c s t a i n l e s s s t e e l s , 304, 316, a n d 3 1 0 , w e r e  selected  f o r load  solutions.  relaxation  stress  Circumferentially  corrosion  notched  equilibrium  yielding  stress  washed  i n hot tap water, d r i e d with  Electron corrosion the  with of  product  a n d Tromans  products simple  diffraction  p r o d u c t was  corrosion  Birley  Following  in situ,  electron  an energy  stripped  ethanol  employed  diffraction dispersive  camera.  and s t o r e d  the metal.  electron  in a  e l e c t r o n microscope  X-ray  s p e c t r o s c o p y was  was  desiccator.  The t e c h n i q u e studies  until  surface  of the fracture  for diffraction  microscope  loaded  on t h e m e t a l s u b s t r a t e  spectrometer attached  electron  then  chloride  i n the t e s t  the. f r a c t u r e  spectroscopy  in situ from  temperature,  corrosion,  whereby a t r a n s m i s s i o n  chamber o f a s c a n n i n g  2.2  performed  [ 1 2 ] was  the transmission  were  and x-ray  in boiling  s t e e l r o d s were p l a c e d  environment, allowed t o reach occurred.  tests  surface  a n d on of  of  corrosion  i s used  as a  conducted  t o the d i f f r a c t i o n  chamber  (T.E.M.) a n d t o t h e s p e c i m e n  microscope  (S.E.M.)  Conventional transmission  electron microscopy  c o n d u c t e d on t h e s t r i p p e d  oxide  and d i f f r a c t i o n  studies  films.  Materials  2.2.1 The analyses  Steels s t a i n l e s s s t e e l s were r e c e i v e d i n weight percent  a r e shown  a s 3/8  inch  i n Table I I .  diameter rods.  The  - 12. -  TABLE  I I : Composition o f Stainless  r Element  304 wt  !  %  i  Steel  —  ! |  316 wt %  i  1  j  310 wt %  i  Fe  69 .89  Cr  18 .67  Ni  8 .91  c  0  Co  0 .1  I  65 .84  17 .92  1  49 .82  |  25 .74  j  21 .57  \  |  11  .61  l f  .05  0 .045  0 • 09  0 .1  0  Cu  0 .2  0 2  Mn  1. -2.  1.--2.  Mo  0 .2  2 0  Si  0.5 -1.0  0.5-•1.0  0  j  i  I  l  2  \  i  i  1.--2.  1 i  0 2 0.5-•1.0  •  TABLE  V  0 .03  0. 03  0 03  s  0 .006  0. 013  0. 006  III: A n n e a l i n g Data f o r S t a i n l e s s  1  j J j  Steel  Steel  Temp. ° C  304  1150  1  65,000  316  1150  1  63,500  310  1150  1  69,000  Time ( h r )  Room Temp. N o t c h yield stress , (psi)  - 13  2.2.2  -  Environments  Four d i f f e r e n t +  e n v i r o n m e n t s were u s e d i n t h i s  1)  MgCl  2)  MgCl^  + HCl +  water  3)  MgCl  2  + FeCl  3  +  water  4)  MgCl  2  + CoCl  2  +  water  2  study;  water  A l l w e r e made w i t h r e a g e n t g r a d e c h e m i c a l s a n d d i s t i l l e d T e s t s were c o n d u c t e d a t t h e b o i l i n g usually  fluctuating  The b a s i c  e n v i r o n m e n t was  i n an a c i d i f i e d  was  t o 40  concentration  same a s B i r l e y ' s MgCl2"6H 0, and  solution,  M/l HCl.  [ 1 7 ] and  The  % MgCl  and water  2  solution  2  MgCl  2  + FeCl  [ 1 5 ] ; 8 wt  distilled  to give  water  37.5% an  solution  3  FeCl3 w i l l  decrease the time t o f a i l u r e ,  stainless  steels  in boiling  chloride  potential  a t 25°C  than F e  + 3  [24],  solutions,  then C o C l  Therefore,  C 0 C I 2 was  added  mole r a t i o  Mg  as t h e mole r a t i o  The  c o m p o s i t i o n was -17  2  and  might  Co  also  t o M g C l 2 t o make a s o l u t i o n  gr C o C l * H 0 , 2  2  Mg  203  Z  was  /Fe  0  + 2  T^, has  of  % point austenitic  a higher  decrease  reduction  T . f  h a v i n g t h e same  i n the FeCl3  gr MgCl «6H 0, 2  solution  the  the b o i l i n g  Since  154°C).  approximate  2  to adjust  point  HCl  % F e C l ^ . 6 H 0 , 67 wt  125°C.  /Co  temperatures  (boiling  l c c of concentrated  MgCl  Baker's  sufficient  2  to  45 wt  cc o f the b a s i c  o f 0.3  o f the s o l u t i o n s ,  ± 2°C.  For t e s t s added  point  water.  2  solution.  boiling  point  160°C.  2.3  Specimen Stress  Preparation  corrosion  specimens  rod, threaded at either  were 7 i n c h  end w i t h a c e n t r a l l y  sections located  o f 3/8 60°  diameter  circumferential  -  notch,  machined t o a  0.2  specimens were a n n e a l e d notched in  stress  reflux  supplied  by  The outside  corrosion tests  cell  tight  and the  electrical  notch and  the  was  the upper  one  environment  prevented  30 the  minutes. expansion  s p e c i m e n was equilibrium the  notch  being  on  the the  this  o f the  at  the  25-30 v o l t s  oxide,  133  are  listed  d.c.  cc a c e t i c  i n a Pyrex  The  F i g . 2.  T e f l o n t a p e , was T e f l o n bungs, The  I n s t r o n and  acid,  added a t  with  an  Heat  was  A  freezing  i t s boiling This  time  l o a d was  a slight  applied to  the  was  the  being  fixed  wrapped to the  reflux  i n t r o d u c i n g the on  the w a l l s of the  g e n e r a l l y took applied to  at  initiate the  the  cell least .  counteract  t o monitor  solution.  s t r e s s ) and  in  lower  p o i n t and  t o h e a t i n g and  equilibrium with  surface  placed  the  cell  to  equilibrium.  (see Table, I I I f o r y i e l d  IV.  The  the  connected  prior  s o l u t i o n , from  l o a d was  cell  specimen, with  a loose f i t .  due  i n Table  corrosion tests.  h e a t i n g tape  specimen  i n thermal a tensile  annealing,  tape.  with  set i n the  thermal  During  The  tested.  thermometer, see  follows:  e n v i r o n m e n t was  to reach  chromic  performed  ends s e a l e d w i t h  Turning  allowed  gr  for stress  covered  heating tape,  The  25  heating  as  area  condenser.  cell.  used  condenser and  procedure  Pyrex  with  an  the  solution;  s.c.c.  After  electropolished  environment were c o n t a i n e d  attached  the  Tests  m o d e l I n s t r o n was  specimen and  III.  stored in a desiccator u n t i l  Stress Corrosion The  to localize  according to Table  r e g i o n o f e a c h s p e c i m e n was  7 cc water, then  floor  -  inch diameter  a chromic-acetic acid  2.4  14  Upon  yielding crosshead  when  the  reaching within of  the  TABLE -IV: S t r e s s C o r r o s i o n Alloy  !  Test  Performed  Environment  304  MgCl  2  304  MgCl  304  Temp. ° C  (boiling)  154  2  + HCl  154  MgCl  2  + FeCl  304  MgCl  2  + CoCl  316  MgCl  2  MgCl  316  (boiling)  .  Type  o f Test  s.c.c.  full  and p a r t i a l  s.c.c.  full  failure  (boiling)  125  s.c.c.  full  failure  (boiling)  160  s.c.c.  full  failure  (boiling)  154  s.c.c.  full  failure  2  + HCl  154  s.c.c.  full  failure  MgCl  2  + CoCl  160  s.c.c.  full  failure  310  MgCl  2  (boiling)  154  s.c.c.  full  failure  310  MgCl  2  + HCl  154  s.c.c.  full  failure  310  MgCl  2  + CoCl  160  s.c.c.  full  failure  316  3  2  (boiling) (boiling)  2  (boiling)  2  (boiling)  failure  Fig.  2.  S.C.C. c e l l  with  7  inch long  specimen  in  place.  -  Instron at  then  the root  relaxing surface  locked.  A circumferential stress  o f the notch  and propagated  devoid  of overload  failure.  a n d t h e two f r a c t u r e  solution,  then  dried  Partially  cracked  with  temperature  s u r f a c e s washed  to one-half  o f the specimen,  s.c.c.  fracture  The s p e c i m e n was r e m o v e d  ethanol prior  were n o t w a s h e d , b u t p l a c e d mechanically  a wholly  immediately  i n a desiccator.  from t h e environment  the i n i t i a l  from t h e  i n h o t t a p w a t e r t o remove t h e  to storing  specimens were removed  l o a d had dropped  corrosion crack o r i g i n a t e d  t o the centre  the l o a d t o zero, and producing  environment  the  17 -  value.  These  when  specimens  i n a d e s i c c a t o r and  later  f r a c t u r e d i n a H o u n s f i e l d Tensometer a t 25°C, a t which the crack  solution  i s a solid  hydrated  product  a n d may b e  e x a m i n e d i n t h e S.E.M.  2.5  Corrosion The  Product  fracture  Stripping  surface  corrosion product  methods;  1) d i s s o l u t i o n  solution  a n d 2) m e c h a n i c a l l y  cellulose  o f the metal  v o l % bromine,  5%  bromine  the  but this  that  i n a bromine-methanol  the corrosion product  s u r f a c e s was  i s a very  i t might  immersed  with  floated  aggressive  free  After  softened  i n acetone,  was p r e s s e d  onto  stripped  o f f when i t h a d h a r d e n e d .  [14] used  solution  solution  i n the solution  s u b s t r a t e a n d was  Cellulose  the other  a  and t h e r e  The 1% b r o m i n e  a few h o u r s  o f the metal  i n s u c c e s s i v e s o l u t i o n s o f methanol.  i n a solution of  Nielson  damage t h e o x i d e .  a n d was . q u i t e s a t i s f a c t o r y .  corrosion product  washed  stripping  99 v o l % a n h y d r o u s m e t h a n o l .  solution  was some c o n c e r n was u s e d  substrate  different  acetate.  One o f t h e two f r a c t u r e 1  was s t r i p p e d b y two  acetate  fracture  The r e s u l t i n g  acetate  sheet,  s u r f a c e and replica  was  -  coated with leaving  dissolved  a carbon r e p l i c a with  The of  carbon, then  18 -  the stripped  a n d washed  corrosion  in.methanol  product  two s t r i p p i n g m e t h o d s , p e r f o r m e d o n s e p a r a t e  t h e same s p e c i m e n , p r o v i d e d  the  i n acetone  attached.  fracture  surface  a means o f t e s t i n g t h e v a l i d i t y  of usin  b r o m i n e - m e t h a n o l method t o s t r i p  corrosion  products  f o r chemical  analysis.  2.6  Electron  Diffraction  Electron  d i f f r a c t i o n studies  product, both transmission  in situ  products in  microscope  the technique  i n situ.  The s t r e s s  the high resolution  macroscopic  s.c.c.  Diffraction  patterns  surface of  and s t r i p p e d ,  electron  [12,17] d e s c r i b e d  t h i s technique  were p e r f o r m e d  (T.E.M.).  corrosion  were  surface  o n a 100 k v  diffraction of  fractured  Hitachi  corrosion  s p e c i m e n was  placed  o f t h e T.E.M. w i t h t h e  plane p a r a l l e l  to the electron  o b t a i n e d when p r o t u b e r a n c e s  the electron  corrosion  B i r l e y and Tromans  f o r electron  d i f f r a c t i o n stage  fracture  intersected  of the fracture  beam, s e e F i g . 3.  beam.  on t h e f r a c t u r e  The a d v a n t a g e s  were;  1) i t p e r m i t s e x a m i n a t i o n o f t h e c o r r o s i o n  f i l m without  any p r i o r  treatment. 2) t h e r e electron heat  sink  i s less  beam w i l l  l i k e l i h o o d that  heating  damage t h e c o r r o s i o n  provided by the metal  effects  product  from t h e  because  of the large  substrate.  3) t h e r e l a t i v e i n t e n s i t i e s o f t h e d i f f r a c t i o n r i n g s to  those  f o r randomly  Stripped  oriented  corrosion  films  are similar  powders. were mounted on specimen m o u n t i n g  grids  - 19  ELE  -  CTRON BEAM  S.C.C. FRACTURE SURFACE  X-RAYS  DIFFRACTED BEAM  F i  S-  3.  Schematic r e p r e s e n t a t i o n o f i n s i t u d i f f r a c t i o n o f s u r f a c e o x i d e i n h i g h r e s o l u t i o n d i f f r a c t i o n stage o f the T.E.M. The p r i m a r y e l e c t r o n beam s t r i k e s t h e s u r f a c e f i l m and i s d i f f r a c t e d .  -  for  the  T.E.M., t h e n p l a c e d  and  diffraction  stripped  films  were t o o t h i n s.c.c.  Ortec with  from  the  s u r f a c e was  carbon  2.7.1  Introduction  X-ray  s p e c t r o s c o p y was dispersive  from  intensity  t o an  150-200A .  The  0  atoms.  the e l e c t r o n  produced  beam c u r r e n t  are  conducted  (10  i  by  0  The  an  electron  wavelength  law;  ^ = 2d  angle  of diffraction  The  chemically-  fracture  surfaces  probe.  hkl  and  S.E.M. u s i n g  The  S.E.M.  surface.  i s produced  small by  k n o c k an  x-ray i n t e n s i t y  low  7  probe Amps).  o f the  which has The  energy  resulting  electron from the  a relatively and  secondary  the x-ray  high  identification  x-ray spectrometer o f which and  energy  there  dispersive.  s p e c t r o m e t e r (W.D.S.) i s b a s e d  , where d i s t h e i n t e r p l a n a r A i s the wavelength  of  diameter,  orbital  detection  an  equipped  image o f t h e s p e c i m e n  image  dispersive  dispersive Sin©  product attached.  function  and  The  Upon  primary  current  electron  unless the  to stripping.  (E.D.S.).  a low  The  Amps v s . 10  types, wavelength  Bragg  microscope  beam o f t h e S.E.M. i s l o w e r t h a n  the x-rays i s the f u n c t i o n two  steel  i n t h e T.E.M. a n d  c r e a t e d when p r i m a r y e l e c t r o n s  by  areas.  with the corrosion  a high resolution  the surface  excitation  of  free  p r i m a r y e l e c t r o n beam h a s  free  stainless  x-ray spectrometer  a n E.D.S. i s s i m i l a r  electrons,  selected  carbon coated p r i o r  floated  Spectroscopy  approximately  316  stage o f the  detected i n the bromine-methanol s o l u t i o n  S.E.M. i s t o p r o d u c e The  i n the specimen  304- a n d  X-ray  energy  -  obtained from  the  t o be  fracture  stripping  2.7  patterns  20  of the  on  spacing, 0  radiation.  the i s the  the  -  X-rays of  originating  specific  Since  each  from  Only  a  can be performed  x-rays  rate,  a large  counter.  a larger  diameter  resolution  above  will  satisfy  t h e Bragg  Therefore, t o achieve  which  a n d makes t h e W.D.S. u n s u i t a b l e  o f the wavelength  For this  normally  f o r instruments  spectrometer  normal  i s time  t o t h eprimary  Energy  dispersive  t h e complete  consuming and t h a t  electron  beam t o e n s u r e  chemical  t h e specimen h i g h count  t o i t s energy.  counters,  or a solid  This  state  detector i sa l i t h i u m  canbe achieved with  crystal drifted  detector. silicon  flow  analysis  surface  must  radiation  proportional  For theOrtec  crystal  ratios.  rates.  spectrometers separate c h a r a c t e r i s t i c  according  series  i s good, e g . c h a r a c t e r i s t i c  10 eV a p a r t c a n b e s e p a r a t e d w i t h h i g h p e a k t o b a c k g r o u n d  o f a n unknown s p e c i m e n  E.D.S.,  Si(Li),(Ortec  7000T).  When a n x - r a y from  by scanning  volume o f x - r a y s must b e g e n e r a t e d .  m a j o r d r a w b a c k s t o t h e W.D.S. a r e t h a t  the  A,  t h e S.E.M. The  The  A l l elements  t h e p r i m a r y beam must h a v e a h i g h beam c u r r e n t  requires like  x-rays, wavelength  o f the x-rays produced  a n d b e p i c k e d up b y t h e c o l l i m a t e d  reason,  by a counting d e v i c e .  o n a n unknown s p e c i m e n  o f angles.  crystal  crystals.  a small fraction  good c o u n t  be  a range  by an a n a l y z i n g  a t o m i c number 4, c a n b e d e t e c t e d w i t h t h e u s e o f v a r i o u s  diffracting  law  s p a c i n g d ^ ^ and monitored  spectrometer through  beryllium,  ared i f f r a c t e d  has a s e t o f c h a r a c t e r i s t i c  elemental analysis the  the specimen  interplanar element  21 -  the s i l i c o n  3.8 eV o f e n e r g y .  from  t h e specimen  atoms a r e e x c i t e d . Thus, a s i n g l e  hits  the Si(Li)  Each  excited  x-ray photon  crystal,  electron  excites  electrons  absorbs  many e l e c t r o n s ,  which  -  are  collected,  energy in the  o f the  o f the  i na current that i sp r o p o r t i o n a l t o t h e  photon.  analyzer  current f o r every  other  T h i s c u r r e n t charge (M.C.A.) w h i c h x-ray  striking  the  1)  advantages theentire  displayed  o f the x-ray  E.D.S.  spectrum  s i m u l t a n e o u s l y , thus  stores  crystal.  o f frequency  In the present  The  vs.  energy  s t u d i e s an  are; generated  total  may b e a n a l y z e d a n d  elemental  analysis  may b e done  a few m i n u t e s . 2) b e c a u s e n o c o l l i m a t i o n  produced  are  analyzed.  i snecessary,  This allows  beam c u r r e n t s a s s o c i a t e d w i t h 3)  specimen p o s i t i o n  wavelength The 1)  dispersive  only elements  a high percentage  t h e E.D.S. t o b e o p e r a t e d  scanning  and topography  electron  are  o f x-rays with the  microscopes.  n o t as c r i t i c a l  as f o r  spectrometers.  disadvantages  2) r e s o l u t i o n by  Si(Li)  and stored  m o d e l 6200 M.C.A. was e m p l o y e d . The  low  the  spectrum  crystal.  i samplified  simultaneously  striking  analyzer i sa continuous  a l l x-rays  Ortec  in  x-ray  a multichannel  output for  resulting  22 -  are; above  sodium, atomic  i sinferior  t o the  number 1 1 , c a n b e a n a l y z e d .  W.D.S.; g e n e r a l l y o n l y p e a k s  separated  160 e V o r more may b e r e s o l v e d . 3) p e a k t o b a c k g r o u n d r a t i o s It  presence  s h o u l d be n o t e d o f elements,  or covalent state. product  t h a t x-ray  areinferior energy  t o t h e W.D.S.  analysis  only  a n d conveys no i n f o r m a t i o n about  F o r example c h l o r i n e  may b e p r e s e n t  a n d o n e may h a v e t o assume i t i s p r e s e n t  detects their  the.  ionic  i na corrosion  as a c h l o r i d e .  -  2.7.2 The x-ray  X-ray usual  Spectroscopy  intensity  spectroscopy,  models t h a t r e l a t e  do  vs  hold  assumption t h a t  f o r very  can  pass t o the  surface with  The  validity  transmission transparent fluorescence voltages not  In  effects  i n the  affect  the  must be  the  while  be  same t h i c k n e s s  For possible it  For  c o r r e c t i o n f a c t o r s are as  the  get  an  possible to obtain  topography  o f the  use  a  oxide.  o f the  increase  beam  fluorescence. used  i n 40-100  kv  i f the  specimen  is  lower  and  electron  e l e c t r o n s c a t t e r i n g but  of thick materials  be  x-ray  intensities s p e c i m e n and  as  there  absorption  p e r f o r m e d by of  and  comparing  standards,  standards  the  still  be  specimen.  negligible,  is  fluorescence  and  applying  excited are  some  a p p l i e d but For  standards  no  specimen  are  s p e c i m e n s where t h e r e  trans-  the  very  thin  must  also  specimen.  f i l m s from the  accurate  foils  the  produced.  thinner  same t h i c k n e s s  the  g e n e r a t e d by  general,  c o r r e c t i o n f a c t o r s may  corrosion product to  The  considerable  to elemental  b a s e d on  and  with  mathematical  electronbeam, absorption  x-rays  a n a l y s i s can  x-rays  In  The  are  for thin  spectroscopy  conditions.  films, the  of  films.  absorption  [25].  ignored.  f a c t o r s , providing both  e l e c t r o n s the  standard  negligible  (20-30kv) s h o u l d  x-ray  elemental  under s i m i l a r mitted  be  thin  specimens the  transmission  can  corrections associated  concentrations  been v e r i f i e d  absorption  intensities  correction  to  thin  e l e c t r o n beam a n d  Quantitative elemental  kv  S.E.M.  conventional  transmitted  f o r very  electron miscroscopy i n a 100  Films  concentration  not  has  -  of Thin  intensities  of this  23  fracture surface  measurement o f t h e  standard Since  which would x-ray  film  will  not  t h i c k n e s s , nor  d u p l i c a t e the  intensity  i t is  vary  is  surface with  thickness  -  and  roughness,  stress is  24 -  as w e l l as composition,  corrosion  fracture  quantitative  surface corrosion  product  quantitative produced  analysis  of thin  i n the thin  intensity  ratios  by x-ray  spectroscopy  efficiency  spectroscopy  i s not possible,  s e c t i o n s can be done.  elements  assuming s i m i l a r  i s similar  f o r elements diffraction  will  excitation  with  p a t t e r n s from  provide  a n a d e q u a t e means o f c o r r o s i o n ' p r o d u c t  atomic  o f the primary  films  beam w i l l  specimen h o l d e r t h e f i l m  through  i s mounted on.  where t h e y w i l l  characteristic support  grid  resulting  x-rays.  produce  further  Thus, x-rays  and a r e a s remote  from  corrosion graphite  film  to avoid this on a s u p p o r t  cylinder.  cylinder will the hollow  t h e specimen  be d e t e c t e d f r o m  x-rays  both the (see F i g . 4 ) ,  generated  from  carbon.  over  a hole  i n a hollow  of hitting  analytical  the bottom o f t h e hollow  .back-scattered e l e c t r o n s which w i l l  instead  support  i n v o l v e d mounting t h e s t r i p p e d  Transmitted electrons s t r i k i n g  generate  cylinder  grid,  and s t r i k e t h e  and g e n e r a t i o n o f  Characteristic  problem  a good  'Back-scattered e l e c t r o n s w i l l  s p e c i m e n h o l d e r may b e e l i m i n a t e d b y c o a t i n g w i t h - Attempts  that  t h e p r i m a r y ' e l e c t r o n beam,  i n misleading analyses.  product,  Spectroscopy  the film  excitation will  These  identification.  r e f l e c t e d from t h e . specimen h o l d e r back towards  grid,  numbers).  i t must be remembered pass  (excitation  the corrosion  M o u n t i n g o f T h i n F i l m s f o r S.E.M. X - r a y  When d e a l i n g w i t h t h i n  to their  efficiency  similar  together with  portion  x-rays  be p r o p o r t i o n a l  ratios,  2.7.3  Since  semi-  sections are not subject t o absorption a f f e c t s , the  of different  concentration ratios  the  of the  not possible. Even though q u a n t i t a t i v e  be  analysis  the corrosion  film  be absorbed i n (seeF i g . 4 ) .  E L E C T R O N BEAM  SPECIMEN COPPER GRID  GRAPHITE  BLOCK  BACKSCATTERED ELECTRONS  ELECTRONS X-RAYS  Schematic diagrams o f b a c k s c a t t e r e d e l e c t r o n holder during x-ray a n a l y s i s o f t h i n f i l m s a) from c o n v e n t i o n a l specimen h o l d e r b) from hollow graphite block  effect  from  specimen  -  This  d i d not t o t a l l y  effect  Procedure  X-ray placing  the stress  advantage  stage  corrosion  to  Spectroscopy  surface area  fracture  s e t u p was t h a t  were o b t a i n e d from  surface  f o r X-ray  t h e sample  product  i n s i t u was p e r f o r m e d  surface i n the high  o f t h e T.E.M. f i t t e d  of this  with the Ortec  diffraction  x-ray  analyzer.  However  c o v e r e d b y t h e beam i n t h e T.E.M. was l a r g e r  than t h e  phases  of different  The  analysis  i n t h e same p i e c e o f e q u i p m e n t .  neighbouring  by  resolution  p a t t e r n s and chemical  a r e a c o v e r e d b y t h e beam i n t h e S.E.M., t h u s  isolate  and x-ray '  the situation.  spectroscopy o f the corrosion  diffraction  the  e l i m i n a t e t h e '. b a c k s c a t t e r e d e l e c t r o n  b u t d i d improve  2.7.1  26 -  i t was n o t p o s s i b l e  composition  i n the corrosion,  film. X-ray The  analysis  o f the stripped  surface  was m o r e i n v o l v e d .  diffraction  electron  i n t h e S.E.M.  i t was p o s s i b l e  T.E.M. a r e a s  All  i n t h e T.E.M., w h e r e d i f f r a c t i o n  f e a t u r e s were s t u d i e d , t h e n p l a c e d o n t h e h o l l o w  examination  S.E.M.,  that  t o perform  beam v o l t a g e s e t a t 20 k v . was p e r f o r m e d  and C r / N i r a t i o s  graphite  spectroscopy p a t t e r n s , thus  obtaining electron  comparison  the x-ray  the background  were d e t e r m i n e d  o f the  o f t h e same a r e a .  Qualitative  by i n t e g r a t i n g  cylinder  on p r e - s e l e c t e d  i n T.E.M. a n d S.E.M., was p e r f o r m e d  eV/channel) and s u b t r a c t i n g  Cr/Fe  x-ray  gave good d i f f r a c t i o n  analysis,  p a t t e r n s and  With t h e m a g n i f i c a t i o n c a p a b i l i t i e s  patterns and elemental a n a l y s i s  x-ray  intensities (40  product  s t r i p p e d p r o d u c t , m o u n t e d o n s p e c i m e n g r i d s , was e x a m i n e d b y  conventional techniques  for  corrosion  i n this  peaks  intensity. manner.  with the o f element  over  .5 c h a n n e l s  A l l quoted  -  3. 3.1  Stress The  General Fig.  stress  5.  On  relatively the  type  of  crack path  the  stress  the  varied;  transgranular  scale,  type  fracture  corrosion  fracture  a macroscopic  316  OBSERVATIONS  Tests  corrosion  flat,  304  are  310  surfaces  310  some i n t e r g r a n u l a r  are  fracture  type  304.  316,  and  V.  in  surfaces  were  irregular,  and  The  corrosion  stainless steels,  for  i n Table  shown  were v e r y  were s i m i l a r t o for  summarized  micrographs  type  fracture  surfaces  tests  surface the  transgranular  with  -  RESULTS AND  Corrosion  results  27  stress  predominantly  a m i x e d mode f a i l u r e  for  304. The'type  310'stress  green  corrosion  straw  l u s t r e and  corrosion  deposit. d i d not  The  fracture  304  and  appear to  316  same f o r a l l t h e  solutions,  stress  except  where  ~  Stress  corroded  for  hours  40  removed  thick  brown c o r r o s i o n  specimens not  noticeably  acidified  MgCl  2  acidified  forming  of  304  upon  a  smooth  MgCl  2  and  by  i n the  to  corrosion  MgCl  2  covered remain  thicker  a thick  surfaces  specimens t e s t e d  allowed  areas the  the  solution  grey-black  s l o w e d and  had  +  had  a  film.  i n the  FeCl3 the  blueshiny These  various  solution  fracture  i n the  corrosion  MgCl2 film  surface. solution  than  specimens  fracture.  affected  solution  thick  product  form a n o t i c e a b l y  stream of bubbles, b e l i e v e d reaction  corroded  exposed e l e c t r o p o l i s h e d  were n o t  the  red  immediately  The  in  did  304  fracture  have a  o b s e r v a t i o n s were t h e  surfaces  the  various  surfaces  solutions,  of  the  electropolished  be  stopped within  H  2  film  gas.  and No  areas  producing  p i t t i n g was  approximately  one  the  specimens  except  MgCl2 + F e C l 3 s o l u t i o n .  corrosion to  on  hour.  On  the immersion  reacted, a  steady  observed. The  This  exposed  surface  TABLE  V:  Stress Corrosion Steel  Test  # o f Spec.  304  3  304  1  304  Results Load ( p s i )  61400/63200/65700  Environment  MgCl  2  59000  MgCl  2  1  61000  MgCl  2  +  FeCl  304  1  72000  MgCl  2  +  CoCl  316  3  MgCl  2  316  1  54800  MgCl  2  + HCl  316  1  63400  MgCl  2  +  310  3  MgCl  2  310  1  71900  MgCl  2  + HCl.  310  1  68900  MgCl  2  +  66000/63500/65800  85800/82600/82500  Temp. ° C .  154  74/99/89  154  76  3  125  150  2  160-  +.HC1  154  CoCl  2  2  :  210  200/160/240  154  230  160  250  154  CoCl  Time t o F a i l u r e (min)  2130/2436/2172  154  2012  160 •  1910  - 29  F i g . 5.  -  R e p r e s e n t a t i v e f r a c t o g r a p h s (40x m a g n i f i c a t i o n ) f r o m s t a i n l e s s S t e e l s , a) 304, b) 316, C) 310  -  areas  on  pitted  the  and  304  covered with  small patches  3.2  3.2.1  thin  of  the  the  fracture  fracture  corrosion  of  s p e c i m e n s was after  morphology  spikes  a  few  The  corrosion  and  t o be  316  corrosion  product  s u b s t r a t e had s u r f a c e was  on  an  the  so  evaporated  carbon  substrate attached to  the  dissolved.  similar  from  s p e c i m e n s were  removed from  sponge, r e t a i n i n g  product  products  coated with  came o f f t h e m e t a l  a thick  310  The  corrosion  the  surface  shape o f the The  to the  corrosion  oxide  f a n s as w e l l as  the  fracture product  observed  by  corrosion  (see F i g . 6). corrosion  0  o n l y be  except  thick  s t r i p p i n g was  too  f o r m e d on MgCl  the  fracture  [26].  successful  on  the  carbon  visually  d e t e c t e d by, e l e c t r o n  crack surfaces of , were v e r y t h i n .  surfaces suggested  Carbon c o a t i n g the  too  t o be  the  + FeCl  not  product  thin  films  c o l o u r on  400-500A  corrosion was  the  hours.  s u r f a c e s had  the metal  from  interference  to  film.  environments,  about  spotted with  heavily  Stripping  [14] showing c o r r o s i o n product  The all  s o l u t i o n were  colour.  s u r f a c e s o f 304  product  support  Nielsen  + FeCl3  Oxides  carbon  surface  MgC]2  r e d brown f i l m  s u b s t r a t e w i t h i n a few  corrosion  310  -  bromine-methanol s o l u t i o n removed the  that  film;  a rough  Bromine-Methanol  the metal stress  i n the  of a blue-green  Stripping  The  specimen  30  as  The  fracture  distinguished diffraction  on and  product the  that  carbon  x-ray  and  The  straw  the  t h e r e were o n l y a  films.  304  film  316  coloured  was  surface  prior  few  areas  was  picked  films,  in  and  spectroscopy.  of up could The  - 31 -  Fig.  6.  Micrograph o f c o r r o s i o n product from f r a c t u r e s u r f a c e of type 310 s t a i n l e s s s t e e l s t r e s s c o r r o d e d i n b o i l i n g M g C l solution. S t r i p p e d i n bromine-methanol s o l u t i o n , ( m a g n i f i c a t i o n 1200x) 2  -  carbon the  coated  film  surface.  32 -  was p l a c e d i n t h e S.E.M. a n d a n x - r a y  Those r e g i o n s w h i c h p r o d u c e d  relocated  i n t h e T.E.M. a n d d i f f r a c t i o n  procedure  f o r 304 a n d 316 c o r r o s i o n  The  corrosion  product  s t e e l was much t h i c k e r intact could  an x - r a y  on t h e f r a c t u r e  than  that  spectrum  patterns taken.  products  proved  the fracture  surface.  easily  be r e d u c e d  t o powder.  The s t r i p p e d Electron  the electron  in  t h e S.E.M. r e q u i r e d i t t o b e h e l d o n t h e s p e c i m e n  the  paste  (carbon dag).  The  product  the case The  ripped x-ray  from  analysis  o f t h e carbon  segments on t h e s u r f a c e .  film in  with  coated  grid  and  difficult apart  corrosion with  a  film  carbon  and c h a r g i n g d i d n o t o c c u r i n than  i n t h e T.E.M.  was s u c c e s s f u l  i n removing the but not too successful  specimens.  a c e t a t e p i c k e d up some c o r r o s i o n p r o d u c t  of the d i f f i c u l t y  carbon  was  t o break  t h e s u r f a c e o f 310 s p e c i m e n s ,  o u t s m a l l segments o f s t e e l  because  the  technique  o f 304 a n d 316  stripped  stripped  Stripping  acetate stripping  corrosion  product  stainless  was b r i t t l e  o f the stripped  S.E.M. a s t h e beam c u r r e n t was much l o w e r  3.2.2 A c e t a t e  in  Heating  analytical  easily  diffraction  in  suspension  the corrosion  spectroscopy  This  product  h e a t i n g and c h a r g i n g caused X-ray  were  s u r f a c e s o f t h e 310  as  beam.  made o f  t o be v e r y t e d i o u s .  o n 304 a n d 3 1 6 , b e i n g  from  study  coated  i n finding  t h e T.E.M. a n d S.E.M.  the fracture  acetate s t r i p the product  product  was d i s s o l v e d  Direct  among t h e s t e e l film  i n acetone.  attached floated  The a c e t a t e s t r i p  surface.  was n o t p o s s i b l e  In order f o rthe stripped  acetate film  the corrosion  from  but also  free  t o be The  a n d was  analyzed, carbon examined  f o r t h e 304 a n d 316  fracture  -  surfaces  had only  33 -  s m a l l amounts o f a t t a c h e d  s t r i p p i n g was n o t a s u c c e s s f u l t e c h n i q u e from these had  surfaces.  more p a t c h e s  The a c e t a t e  strip  product.  Thus,  acetate  f o r removing c o r r o s i o n  films  f r o m t h e 310 f r a c t u r e s u r f a c e  o f c o r r o s i o n f i l m w h i c h were e a s i l y  analyzed  i n the  T.E.M. a n d S.E.M.  3.3  Electron The  Diffraction  electron diffraction  Electron fracture in  diffraction  surface  a l l cases  patterns  a n d c o u l d be f i t t e d  i n t e r p l a n a r spacings  and  Y F e 2 0 3 [ 2 3 ] a r e shown  fracture  surface oxides  in  VIII.  the  Stripped  I n some c a s e s ,  fit  lines  to the spinel.  a rombohedral  pattern.  of this  corrosion products  in  fitted  i n Table  more  more  situ.  (d) and x-ray  Patterns  contained  than  316 f r a c t u r e s u r f a c e s  and s t r i p p e d , were  VII.  diffuse  diffuse  ring  (indicating  2  taken  corresponding  small grain  from d-spacings  rule, size).  p r o d u c e d p a t t e r n s w h i c h were c l e a r e r a n d  patterns  obtained  from c o r r o s i o n  not a l l the d i f f r a c t i o n  These l i n e s  patterns  M2O3 o x i d e  taken  and sharp  ring  in situ  extra lines  films  patterns  faint  c o u l d be  and c o u l d  pattern, or a metal.chloride  from t h e oxide  sometimes c o n t a i n e d  products  pattern lines  were g e n e r a l l y v e r y  o f t h e s t r i p p e d oxide  patterns  FeCr 0j,  were n o t t h e g e n e r a l  o f t h e u n d e r l y i n g a u s t e n i t e due t o t h e t h i n n e s s Examination  f o r Fe^O^,  Sample p a t t e r n s  i n F i g . 7, w i t h  similar  s t r u c t u r e , MgO^.  intensities  quality  (corundum) type  Diffraction  i n situ  from t h e s t r e s s c o r r o s i o n  t o a s p i n e l oxide  a r e shown  usual pattern being  a r e summarized i n T a b l e V I .  obtained  corrosion product  The  Table  results  o n 304 a n d  produced by  o f the oxide  diffraction  on t h e s e  i n t r a n s m i s s i o n showed from both  t h i c k areas  surfaces.  both and t h i n  TABLE  V I : Summary o f E l e c t r o n Alloy  Diffraction Environment  304  MgCl  304  Results Oxide  Structure  s.c.c..  fracture  surface  W0  MgCl +HCl  s.c.c.  fracture  surface  M3O4  304  MgCl +HCl  exterior  304  MgCl +CoCl  304  MgCl +FeCl  304  MgCl -fFeCl  316  MgCl  2  s.c.c.  fracture  surface  M3O4  316  MgCl +HCl  s.c.c.  fracture  surface  M3O4  316  MgCl +HCl  exterior  316  MgCl -K;oCl  310  MgCl  310  2  2  2  2  2  2  2  3  3  2  2  specimen  surface  3  k  M0 3  h  s.c.c.  fracture  surface  M3O4  s.c.c.  fracture  surface  M3O4  exterior  specimen  surface  speciment  surface  K 0 /M 0 2  3  M3O4  s.c.c.  fracture  surface  M3O4  s.c.c.  fracture  surface  M 04  MgCl -t-HCl  s.c.c.  fracture  surface  M0  310  MgCl +HCl  exterior  310  MgCl -fCoCl  2  2  2  .  2  2  2  2  s.c.c.  specimen fracture  surface surface  3  3  h  M3O4 M3O4  3  h  Table  VII.  d - S p a c i n g s and R e l a t i v e o f I r o n , FeaOit, Y F e 0 , D i f f r a c t i o n Cards 2  3  4.85 2.966 2.53  t  2  3  A°  2  Y-Fe 0  Fe 0^ d  I n t e n s i t i e s f o r the Spinels F e C r 0 i , f r o m ASTM X - r a y  I/Il  hkl  d  40 70  111 220 311  5.90 4.82 4.18  222 400  3.73 3.41 2.95 2.78 2.64  2.49 2.096  100 10 70  1.712 1.614 1.483  60 85 . 85  422  1.327 1.279 1.264  20 30 10  620 533  1.211 1.1214  20 30  1.0922  60  1.0489 0.989  40  0.962  333/511 440  622 444  A°  2.52 2.41 2.32 2.23 2.08  F e C r 04  3  2  hkl  d  2 5 1  110 111 200  5 2 34  210 211  4.83 2.95 2.51 2.08 1.91 1.71  I/Il  -  220 221 310 311  19  100 1 6 .5  222 320 321  .5  400 420  642 553/731  1.87  10  800 660/822  1.70 1.61  40  555/751  1.55 1.53 1.48  .5 . 1 53  432/520  1.43 1.32 1.27  1 7  433/530 620 533  1.26 1.21  24 12 33  11 3 5  1.12  7  1.09 1.07  19 1  422 511/333 521 440  622 444 642 553/731 650'  A°  1.61 1.49 1.33 1.28 1.21 1.17 1.12 1.08 1.05 0.965 0.933  I/Il  hkl  50 50 100 50 75 25 75  111 220 311  75  440  10 50 25 10 10 50  400 331 422 511/333 620 533 444 • 711/551 642 731  25  800  50  751/555 840  25  •  Fig-  7.  Sample surface  diffraction oxides,  a)  patterns 304,  b)  from  stripped  316,  C)  310  stress  corrosion  fracture  Table  VIII.  D, a n d d - S p a c i n g s o f D i f f r a c t i o n  304 p a t t e r n  #23462  316  D in.  dA°  0.38 0.61  4.74 2.95  M W-M  0.72 0.75 0.81  2.50 2.40  S W  2.22*  0.85 0.94  2. .2 1.92  WW M W  1.06 1.13 1.23  1.70 1.60 1.46  W W-M  1.29  Patterns  pattern  #23404  D i n .  dA°  0.385 0.45 0.64  4.96 4.24* 2.98  0.745 0.785  2.56 2.43  0.90 0.985 1.02  2.12 1.94 1.88*  W-M  1.1 1.17  1.74 1.63  1.40  W  1.28  1.36  1.32  1.42 1.49  1.27  WW W  1.335 1.425  1.49 1.43 1.34  1.54  1.21 1.17  S- s t r o n g M- medium W- weak VW- v e r y weak WWvery, very  Shown i n F i g . 7  W  1.48  1.29  VW  1.56  1.22  310  pattern  Di n .  dA°  M WW  0.40 0.53  4.78 3.60*  M S  0.65 0.77  2.94 2.48  I/Io  W M  does  S Dots M VS  0.92  2.08  S  1.91 .  W  1.80* 1.68  1.2 1.31  1.60 1.46  Dots W M  M  1.37  1.39  W  VW  1;46 1.51  1.30  VW W W  1.6 1.65  1.2 1.16  VW W M  WW WW M-W M  weak which  I/Io  1.00 1.06 1.14  D= d i a m e t e r o f d i f f r a c t i o n d= i n t e r p l a n a r s p a c i n g  *- denotes a l i n e  #23418  not f i ti n the spinel  (M3O4) p a t t e r n  1.26  ring  S  W  on d i f f r a c t i o n  pattern  -  areas.  Transformation  under the observed A  -  of a diffuse  i n f l u e n c e of the in this  38  beam, a s  did  not  (acetate)  i n Table  alter  the  IX.  patterns  taken  regions  MgCl  +  s o l u t i o n s are  observed spinel  on  the  not  same s o l u t i o n . formed  in MgCl  stress  corrosion  The there  was  of D  cubic i s the  constant Dd  the and  crystals  t o the  relation  = constant  pattern not  on  a  the  2  +  oxides  Francis  can  made f r o m  a plot  for analyzing  ( K ) , where d  = a  Q  the  oxide  This  formed  patterns  were to  a  duplex in  the  oxides  taken  [22]  from  of  .  D vs  This  2  + k  2  the  2  2  2  a  Q  for  lattice  + k  i s derived  l ),  i f  Francombe[21]  of  (h  patterns +  see  composition  determination  diffraction (h  and  to  electron diffraction  £hkl^  /  and  pattern belongs  were d e t e r m i n e d  The  plane  exposed  oxides.  the  on  stripping  patterns  exterior surface to  a  corresponding  MgCl2  structure.  parameter v a r i e d with  ring  with  distinct  fracture surface  taken from the  from  product.  One  3  spinels.  lattice  Two  FeCl .  nickel be  pattern  s t r i p p e d from the  c o r u n d u m M^O^  between o x i d e s .  lattice  chemically  Chemical  corrosion  s o l u t i o n were s i m i l a r  diameter of the  corresponds  fits  from a  were s i m i l a r .  oxides  i n MgCl  parameters of  a variation  chromium, i r o n  ring  [ 1 4 ] , was  exposed t o a c i d i f i e d  fracture surface  lattice  determined that  other  patterns  + HCl  2  Nielsen  i s shown i n F i g . 8,  shown i n F i g . 9.  formed  observed  The  from  o f specimens  oxides  s t r u c t u r e , the  s t r u c t u r e was  a sharp  diffraction  s t r u c t u r e o f the  surface  3  to  pattern  the  These p a t t e r n s  notch  FeCl  and  s t r i p p e d oxide  crystal  Diffraction  2  observed by  diffraction  (bromine-methanol) s t r i p p e d oxide  d-spacings  pattern  study.  comparison between the  mechanically  ring  2  +  l  2  parameters )  pattern from  taken i s the  in a  where  2  which  the  camera  T.E.M.,  lattice  '  Fig.  8.  Diffraction surface  39 "  patterns taken  oxides  of type  310  a) bromine-methanol b) c e l l u l o s e  acetate  from  stress  stress  strip strip  corrosion fracture  corroded  in  MgCl  2  -  Table  IX.  40 -  D, d - S p a c i n g s , a n d R e l a t i v e V i s u a l I n t e n s i t i e s f r o m D i f f r a c t i o n P a t t e r n s Taken from Bromine S t r i p and A c e t a t e S t r i p O x i d e s ( s e e F i g u r e 8) 310  MgCl  2  - Bromine  Di n .  dA°  0.395 0.52 0.64 0.72 0.75 0.86 0.915 0.98 1.04 1.11 1.18 1.275 1.325 1.47 1.57  4.76 3.62''= 2.94 2.612.51 2.19* 2.06 1.92  strip  Intensity  1.81* 1.69 1.59 1.47 1.42 1.28 1.20  *- d e n o t e s a l i n e  M VW W WW  s WW S WW WW VW M VW VW VW  does  MgCl  2  - Acetate  Din.  dA°  0.475 0.545 0.63 0.78 0.905 1.1 1.26 1.34 1.43  4.86 4.24* 3.67* 2.96 S.55 2.10 1.83* 1.72 1.62 1.48 1.43 1.33 1.28  1.56 1.62 1.74 1.8  w  that  310  Strip  Intensity M Dots Dots M S M Dots W M M Dots Dots W  n o t f i t i n t h e s p i n e l M301+ p a t t e r n s  -  41  _  a)  b)  c)  9.  D i f f r a c t i o n p a t t e r n s taken from exposed n o t c h a r e a s o f specimens a) t y p e 304 i n M g C l + F e C l . M 0 (spinel) pattern. b ) t y p e 304 i n M g C l + F e C l . M 0 ( r h o m b o h e d r a l ) p a t t e r n c ) t y p e 304 i n M g C l + H C l . M 0 (spinel) pattern 2  3  2  3  2  3  h  2  3  k  3  J+2 -  -  parameter, by  and  d  i s the  recording the  \h~klf, ( u s u a l l y pattern  o f the  D = K/a  diffraction  + k  Graphical plots  of  in  The  A p p e n d i x A.  evidence  f o r the  parameters vary  D vs  presence  by  determine  3.4  X-ray The  a  + k  2  + l )"%or  diffraction  relation;  linearity  these  the  2  different  of the p l o t s  crystal  plots  the  oxides  provides  structure.  The  are.tabulated i n Table  g e n e r a l l y higher than Francombe[21].  the  are  shown  overwhelming lattice X.  lattice  They  parameters  This i s probably  inaccuracy of using electron  spectroscopy results  Spectroscopy  spectroscopy t o be  silicon,  are  oxide  and  due  to  diffraction  the patterns  between  time  to f a i l u r e ,  samples  from  the  energy  peaks  alloy  same s p e c i m e n .  films, iron  of chlorine,  showed t h e with  composition,  elemental  lesser  amounts  chlorine.  phosphorous,  T h e y s h o w e d no environment,  part of the  large  S i Ka  molybdenum,  correlation or  between  I n some i n s t a n c e s , a s p e c t r u m  s u r f a c e oxide would have a  another  XI.  Oxides  chromium and  magnesium were i n c o n s i s t e n t .  from  i n Table  molybdenum, magnesium, p h o s p h o r o u s , and  silicon  sample o f f r a c t u r e  summarized  of Stripped  of stripped  predominantly  characteristic  a spectrum  the  values.  Q  X-ray  composition of nickel,  as  (2)  F r a n c i s [22] and  x-ray  X-ray  are  and  settings  and  Spectroscopy  3.4.1  The  and  K i s obtained  a m a t e r i a l o f known d  Thus, the  of a spinel  from  of impurities  to  2  excellent  determined  constant  ) ^  2  (h  presence  inconsistently  determined  + l  2  The  same i n s t r u m e n t  unknown s p e c i m e n . 2  spacing.  p a t t e r n from  gold) at the  (h  D  interplartar  peak.  same o x i d e w o u l d h a v e a  from  a  However,  relatively  -  Table  X.  43 -  a Values C a l c u l a t e d from P l o t s o f D vs ( h + k +l ) ^ i n A p p e n d i x A, where S l o p e M = K / a , M D e t e r m i n e d f r o m Least Squares A n a l y s i s . A l l O x i d e s S t r i p p e d i n 1% B r o m i n e - M e t h a n o l S o l u t i o n E x c e p t Where N o t e d 2  2  2  Q  Q  Alloy  a ( A ° ) f o r oxides i n v a r i o u s environments MgCl + HCl MgCl2 M g C l + Co.Cl 0  2  304  316  310  8.36 8.41 8.39  8.45 8.45  8.36 8.35  8.45 8.38  8.30  8.45  8.36  8.27 8.23  8.36 8.41 310  - Oxide  8.41  *8.38 *8.40 *8.44  stripped with c e l l u l o s e acetate  2  8.52 8.52 8.33 8.49 8.45 8.58 8.45  2  MgCl  2  +  8.52 8.44 8.44  FeCl  3  TABLE X I  CrKa/FeKa 304  MgCl  2  304  MgCl  2  304  MgCl  304 304  fracture  surface  C r , F e , N i ,C1,Mo , P , S i , M g  >1  + HCl  fracture  surface  C r ,Fe , N i ,C1,Mo , P , S i , M g  >1  2  + HCl '  e x t e r i o r notch  Cr ,Fe,Ni,C1,Mo,P,Si,Mg  >1  MgCl  2  +  CoCl  2  fracture  surface  C r ,Fe ,Ni,C1,Mo,P , S i , M g  >1  MgCl  2  +  FeCl  3  fracture  surface  C r ,Fe , N i ,C1 ,Mo ,P, S i ,Mg  variable  MgCl  2  +  FeCl  3  e x t e r i o r notch  Cr,Fe,Ni,C1,Mo,P,Si,Mg  variable  316  MgCl  2  316  MgCl  2  + HCl  316  MgCl  2  +  304  CoCl  310  MgCl  2  310  MgCl  2  + HCl  310  MgCl  2  +  CoCl  2  2  surface  surface  fracture  surface  C r , F e , N i ,C1,Mo,Si,P,Mg  >1  fracture  surface  Cr,Fe,Ni,C1,Mo,P,Si,Mg  >1  fracture  surface  Cr,Fe Ni,Cl,Mo,P,Si,Mg  >1  fracture  surface  Cr,Fe,Ni,C1,Mo,P,Si,Mg  >1  fracture  surface  Cr,Fe,Ni,C1,Mo,P,Si,Mg  >1  fracture  surface  Cr,Fe,Ni,Cl,Mo,P,Si,Mg  >1  s  -  minor  SiKapeak.  t o be  dependent  traces  of  [ 1 7 ] , as oxide.  intensity  upon the  MgCl2, and w e l l as  alloy  s t r i p p e d oxide B.  normalized  with  s p e c t r a , as  alloys  and  c o u l d be  respect  to the  environments  due  fluorescence  to  absorption  caused  Chromium K°< was The the  1.5/1  spectra  various to  related  to  assumption and  of thin  from the  ratios,  10/1  spinel  FeCr2d , +  (see  structure. F i g . 11),  see  from the  and  304  316  However, x - r a y similar  could  spectroscopy  results.  of  Thus, the  be  the  surface  integrated  thought  iron  ranging' from  absorption  high  possible  specimens  negligible  T h i s was  from  the  confirming  very  are  fracture  thus  specimens had  in  variation  result  oxides  fracture  from  the  This  the  and  from these  s p e c t r a from the  text  It i s also of  taken  different  vary.  oxide.  F i g . 10,  i n some c a s e s .  gave  general,  i t could  the  shown  i n the  i n t e g r a t e d CrKa/FeKa r a t i o s  corrosion films,  310  or  f o r m e d on  spectra taken  The  spectra  peak, u s u a l l y . f o l l o w e d by  oxide  patterns,  of the  a  taken  In  rough nature  strongest  effects.  as  the  the  corrosion products  with  peak.  i n the  peak v a r i a t i o n s .  taken  appearing  in  confining attention  s o l u t i o n s are  peak h e i g h t s  the  diffraction  high  the  c a u s e d by  Some o f t h e  fluorescence  as  others  spectra  occurring  e n v i r o n m e n t s had  6/1.  various  as  by  remove  oxychlorides  silicates)  Representative  differences i n composition,  and  oxide  i n the  and  were o b t a i n e d  c h r o m i u m Ka  although  scattering effects  surface  in  sulphides  i n the well  felt  w h i c h samples were washed t o  Ni peaks.  f i l m s formed  These  l o w e r e n e r g y p e a k s was  random p r e s e n c e o f magnesium  Cr,  same e l e m e n t s w e r e p r e s e n t  Kot.  with  i n c l u s i o n s (eg.  more c o n s i s t e n t F e ,  Appendix  that  of these  success  upon t h e  -  Consequently, major deductions  t o the the  The  45  t o be  inconsistent  chromite high  CrKa/FeKa  ore,  integrated  -  Fig-  10.  46  -  D i f f r a c t i o n p a t t e r n and x - r a y spectrum t a k e n from t h e same a r e a on a f r a c t u r e s u r f a c e o x i d e s t r i p p e d from 316-type specimen s t r e s s corroded i n MgCl + C o C l s o l u t i o n . 2  2  Fig.  11.  X-ray  spectrum  taken from  chromite  ore.  -  CrKa/FeKa r a t i o  was  oxide;  film  the t h i n  product  fracture oxide  had a v a r i a b l e ratio  always  >1.  Electron  no d i s t i n c t  The  oxide  MgCl  2  + FeCl  solution  3  formed i n t h e crack.  2  + FeCl  and i r o n  3  of varying  existed  as n o d u l e s  solution  two d i s t i n c t  colour layers  showed t h e gray  side  composite  oxide  oxide  i s a spinel,  formed  chromium  enriched at the solution  varied  there  The o x i d e s t r u c t u r e from  chromium e n r i c h e d  on t h e s p e c i m e n  x-ray  spectroscopy  spectrum  surface i n  as t h e oxide  showed t h e o x i d e  ratios.  the iron  observed  gray  interface.  had a s i m i l a r  while  o f the  are m i s c i b l e [ 2 2 ] , thus  i n t e g r a t e d CrKa/FeKa o f oxide  always  the composite  solution  were  c o l o u r on t h e o x i d e /  of this  could indicate  X-ray  showed t h e  a silver  o f the s i l v e r  diffraction  t h a t formed o u t s i d e t h e crack  regions  The  analysis  the composition  enriched at the oxide  corrosion  this  examination  boundary w i t h i n the oxide.  c o u l d r e m a i n t h e same w h i l e iron  Optical  and a r e d brown  «1 while  interface  solution  coloured layers;  I r o n and chromium s p i n e l s  was. p r o b a b l y  + FeCl3  2  Variations like  oxides.  surface i n the MgCl  a t the metal  interface.  on t h e s t r e s s  A n a l y s i s o f t h e r e d brown o x i d e  a spinel pattern. This  enriched  that  >1.  to  interface,  CrKa/FeKa r a t i o  the s.c.c.  corrosion  S p e c t r a i n F i g . 12 show t h e i n t e g r a t e d  <1  i n any o f t h e o t h e r  showed r a t i o s  produced  the  i n the MgCl  composition.  changes from  interface.  integrated  f o r the t h i c k  o f the corrosion product  on t h e m e t a l / o x i d e  solution  to  invalid  s h o w e d t h a t i t h a d two d i s t i n c t  colour  on  being  i n the  specimens.  spectroscopy  observed  oxide  assumption  s u r f a c e o f 304 c r a c k e d  CrKa/FeKa not  due t o a b s o r p t i o n a n d f l u o r e s c e n c e e f f e c t s  on t h e 310  X-ray  48 -  Chromium  enriched regions  on t h e s t r e s s  rich  contained regions  formed a  c o r r o s i o n crack  layer.  -  ENERGY Fig.  12.  49 -  KeV  X-ray s p e c t r a taken from t h e f r a c t u r e s u r f a c e oxide s t r i p p e d from a t y p e 304 s p e c i m e n s t r e s s c o r r o d e d i n M g C l 2 + FeCl^ s o l u t i o n . The three d i f f e r e n t spectra represent the v a r i a t i o n i n integrated CrKa/FeKa r a t i o o b s e r v e d f o r t h i s o x i d e . a) CrKa/ b) CrKa/ c) CrKa/  FeKa FeKa FeKa  = 4.99/1 = 1.01/1 = 0.405/1  -  surface the  oxide  -  o b s e r v e d on  the  oxide  f o r m e d on  the  exterior surface  of  specimen. X-ray  specimens spectra in  were not  50  s p e c t r a o f the exposed  of  the  Spectra oxide  obtained  characteristic as  bromine had  to  did  not  on  the  MgCl  2  the  s.c.c.  and  from the  310  s t r i p p e d from the  no  1.48  eV  i n the  a bromine L a peak.  with  the  fluorescence  and  strongly alter  the  No  variation  stripped  are  chemically  shown i n F i g . 1 3 .  chemically  o f the  relative  effects).  observed.  A  s t r i p p e d spectrum  the  stripping  was  process  However, t h e heights  major  (which  peaks  could  Thus b r o m i n e - m e t h a n o l  composition  of metal  of  the  and  oxide.  elemental  to  were  i n t o the  absorption  surface  irregularities  Thus d u r i n g  exception  notch  fracture surfaces.  surface  fracture surface  peak a t  outer  s o l u t i o n s were s i m i l a r  mechanically  become i n c o r p o r a t e d  were s i m i l a r , due  formed  were o b s e r v e d  f o r m e d on  identified  to a c i d i f i e d  oxide  peak r a t i o s  oxide  i n the  be  stripping  corrosion  product. The had  that  c h l o r i n e peaks  c o r r o s i o n product  had  not  present,  part  o f the  diffraction to  of  i n a l l the  been washed e x t e n s i v e l y , s u g g e s t e d t h a t  of the  be  presence  a  of the metal  not  [5] suggested  c o r r o s i o n product  formed  for FeCl by  the  2  c h l o r i d e ions  fracture surface.  however, P o u r b a i x  charts  spectra, after  a portion of solidified  been washed from the  c e r t a i n extent  detection  and  x-ray  that  i n s.c.c.  show t h a t  c o u l d be s.c.c.  cracks.  , 2  4H 0 2  see  Table  XII.  o f s m a l l q u a n t i t i e s o f m e t a l c h l o r i d e s by . e l e c t r o n  oxide  w o u l d be  difficult  c h l o r i d e s c o u l d be  present  in this i n the  case.  Hence  corrosion  solution  could  may be  X-ray  i t s p a t t e r n w o u l d be  spinel patterns,  part  Oxychlorides  FeCl  the  masked Thus,  the  diffraction  i t is possible  product.  that  oxide  - 51 -  ENERGY F i g . 13.  KeV  X-ray s p e c t r a t a k e n from f r a c t u r e s u r f a c e o x i d e s t r i p p e d from a t y p e 310 specimen s t r e s s c o r r o d e d i n MgCl2 s o l u t i o n . a) o x i d e s t r i p p e d w i t h bromine-methanol s o l u t i o n b) o x i d e s t r i p p e d w i t h c e l l u l o s e a c e t a t e  -  TABLE XII:  52  -  X r a y I n t e n s i t i e s a n d d - S p a c i n g s f o r TezOi) and F e C l I n d e x C a r d s #11-614 a n d 1-1106 Respectively. Fe 0 3  FeCl  4  2  from  2  dA°  I/Il  hkl  dA°  I/Il  hkl  4.85  40  111  5.9 3.07 2.54 2.32 2.09 1.953  63  003  2.966 2.5 30 2.419 2.096 1.712 1.614 1.483  70 100 10 70 60 85 85  220 311 222 400 422 333/511 440  1.327 1.279 1.264  20 30 10 20 ' 30 60  620 533 622 444 642 553/731  1.211 1.1214 1.0922 1.0489  40  800  1.80 1.721 1.632 1.552 1.467 1.421 1.272 1.173 1.138  ASTM  30 100 7 7 13 63 13 2 4 20 5 3 2 18  101 104 015 N.I. 009 018 112 N.I. 021 0012/024 0111/205 208 0015/211 1112/214  -  3.4. 2  In S i t u Spectroscopy •  It  found  was  products  was  that  substrate. electron  work b y B o l o n  x-rays  e x c i t a t i o n was w i t h i n  and L i f s h i n  t o be p r o d u c e d  fracture  spectra  corrosion  fracture  F i g . 14).  were  taken  surfaces  surfaces  that  these  fracture  surfaces  In  fracture  solutions  were l e f t  films  [28] indicates  diffraction  that of  taken  the s.c.c.  2  from  surfaces  indicated  stripped  oxide  the oxide.  t h e o x i d e was  molybdenum,  o f 310  fracture  the  metal  surfaces  were  enriched  and c h l o r i n e  fracture  o f a l l type  sufficiently  Spectra taken  from  i n chromium and  impurities,  similar  analysis.  the e x c i t a t i o n o f the metal  surfaces  steels  o f 304 a n d  the mechanical  solutions  of  the stress  on t h e 304 a n d 316 s . c . c .  + FeCl3  came f r o m  stage  mechanical  formed on t h e f r a c t u r e  304 i n M g C l  order t o minimize  corrosion  films  to the  o f t h e T.E.M.),  304, 316, a n d 310 s t a i n l e s s  o b t a i n e d from  products  iron with n i c k e l , s i l i c o n , from  stage  m o s t o f t h e x - r a y s , came f r o m  most o f t h e x - r a y s  the r e s u l t s  that  f o r a s i g n i f i c a n t amount  spectra  o b t a i n e d from  product  that  310 s p e c i m e n s a n d t y p e  to  o f type  The s p e c t r a  The c o r r o s i o n  thick  thick  parallel  304, 316, a n d 310 s t a i n l e s s s t e e l s  The c o r r o s i o n  substrate.  was  diffraction  and compared t o x - r a y  were so t h i n  surface  i n thin  corrosion  and n o t t h e m e t a l  In the high r e s o l u t i o n  similar to the spectra  surfaces.  of  sufficiently  the oxide  fracture  on s c a t t e r i n g  spectroscopy  i n the oxide.  type  surfaces,  316 w e r e  corrosion  (as i n t h e h i g h r e s o l u t i o n  T.E.M., f r o m  (see  x-ray  s h o u l d be a b o u t one micron' t h i c k  X-ray the  in situ  u n l e s s t h e o x i d e was  I f the stress  beam  oxide  meaningful  not possible  t h e volume o f x - r a y  the  53 -  i n MgCl  2  i n the bromine s o l u t i o n  substrate,  a n d 304 i n M g C l f o r 24 h o u r s ,  2  +  stress FeCl3  d i s s o l v i n g the  0.5  cn  1.0  0.5  0.0 5 Fig.  14.  Comparison  of i n s i t u  s u r f a c e s , with MgCl2  x-ray  fracture  6  7  ENERGY  s p e c t r a from  s u r f a c e s from  8  KeV  mechanical  specimens  fracture  s.c.c. i n  solution.  a) t y p e  304  mechanical  a') t y p e  304  s.c.c.  fracture  type  316  mechanical  b') t y p e  b)  316  s.c.c.  fracture  c) type  310  mechanical  ") " t y P  310  s.c.c.  c  e  fracture  -  steel  and  in  situ  in  MgCl2  ratios beam at  l e a v i n g the  spectra taken +  FeCLj  from  (see  the  <1  to  surface,  exposed  and  to the  oxide  from the  >1  as  the  This  or the  as  s.c.c.  oxide  could  a  s p o n g e on  surfaces  product  variation  i n the  s p o n g e on CrKa/FeKa  i n t e g r a t e d CrKa/FeKa variation  i n the to a  oxide  occuring  310  ratio  s.c.c.  as  was  the  as  the  c o u l d be  due  observed  i n x-ray  spectroscopy  integrated  of this  was  CrKa/FeKa  due  volume o f  d i d not  ratio  to  oxide from  show  than  the  this beam.  one.  i n the  i n the  the  iron  moved i n t o t h e  gradient  oxide  in  c o u l d be  consistently greater  concentration  The  specimen  spectra taken  i n t e g r a t e d CrKa/FeKa  specimen  304  enriched  surface  oxide  surface.  moved f u r t h e r i n t o  However, x - r a y  the  ratio  i n the  chromium i n t e n s i t y  effects  beam i n c r e a s e s .  the  of the  s p o n g e was  i n d i c a t e an  Increasing  fluorescence  corrosion  Thus, the  -  s o l u t i o n s showed a v a r i a t i o n  F i g . 15).  absorption  The  surface  55  304  oxide,,  s t r i p p e d from the  as fracture  surface.  3.5  the  Partial  Crack  Cooling  a partially  whole  solid. ions  cracked  s o l u t i o n w h i c h was  This hydrate  from the  steel) will  this  solidified  T h e r e was  very  little  the  solidified  of the  crack  be  within  s o l u t i o n from  as the  a i r and  crack  s o l u t i o n had  the  the  to  plus  was  caused  form  a  traces  solidified  crack  hydrated of  crack  metal solution.  unsuccessful.  specimen s u r f a c e  flowed  surface  collected  crack  MgCl2  s o l u t i o n on  from the  partial  the  hydrated  r e f e r r e d to  solidified  i t absorbed moisture Observation  trapped  (predominantly  Stripping  also,  specimen t o room t e m p e r a t u r e  from the  i n the  i n the  and,  surface.  S.E.M. s h o w e d  bottom o f  fissures  a 03.  a  *  <3. a  <j> o  U-  CD  6  ENERGY Fig.  15.  In s i t u  x-ray  spectra  taken  7  8  5  W W  KeV from  fracture  surface oxide of  t y p e 304 s p e c i m e n s . c . c . i n a M g C l 2 + F e C l 3 s o l u t i o n . Shows v a r i a t i o n i n x - r a y s p e c t r u m w i t h beam p e n e t r a t i o n ( a s i n d i c a t e d by i n c r e a s i n g x-ray count r a t e ) a ) C r K a / F e K a = .764/1 (100 c o u n t s / s e c ) b ) C r K a / F e K a = 1.15/1 ( 3 0 0 c o u n t s / s e c ) c ) C r K a / F e K a = 1.40/1 (900 c o u n t s / s e c )  8  -  57  -  on t h e s u r f a c e (see F i g . 1 6 ) . D i r e c t x - r a y s p e c t r o s c o p y o f t h i s  solidified  s o l u t i o n showed l a r g e magnesium and c h l o r i n e p e a k s , t o g e t h e r w i t h s m a l l peaks o f chromium, i r o n and n i c k e l i n t h e same r a t i o as t h e u n d e r l y i n g metal.  T h i s was i n c o n c l u s i v e as i t was p o s s i b l e t h a t t h e i r o n , chromium  and n i c k e l peaks were caused by t h e u n d e r l y i n g m e t a l , and n o t from t h e presence  o f t h e s e elements i n t h e c r a c k s o l u t i o n .  U s i n g t h e t e c h n i q u e s . o f q u a l i t a t i v e aqueous i n o r g a n i c c h e m i c a l i t was p o s s i b l e t o d e t e c t t h e presence ions i n the s o l i d i f i e d crack s o l u t ion  o f f e r r o u s i o n s as opposed t o f e r r i c [29].  Partially  c r a c k e d specimens  were t a k e n from t h e s t r e s s c o r r o d i n g environment and i m m e d i a t e l y fractured.  analysis,  mechanically  A drop o f p o t a s s i u m f e r r i c y a n i d e s o l u t i o n was p l a c e d on one  f r a c t u r e s u r f a c e and ammonium t h i o c y a n a t e s o l u t i o n on t h e o t h e r . P o t a s s i u m f e r r i c y a n i d e t u r n e d t h e h y d r a t e on t h e f r a c t u r e s u r f a c e deep b l u e f o r m i n g a p r e c i p i t a t e , i n d i c a t i n g t h e presence the s o l i d i f i e d crack s o l u t i o n .  o f ferrous ions i n  Ammonium t h i o c y a n a t e s h o u l d t u r n t h e  s o l i d i f i e d c r a c k s o l u t i o n deep r e d i n t h e presence  o f f e r r i c ions but  the o n l y r e a c t i o n was a f a i n t p i n k c o l o r i n d i c a t i n g t h a t t h e f e r r o u s i o n was t h e predominant i o n w i t h i n t h e c r a c k environment. D u r i n g bromine-methanol s t r i p p i n g experiments partially  c r a c k e d specimens o f 310, i t was observed  on washed s u r f a c e s o f t h a t t h e o x i d e removed  from t h e f r a c t u r e s u r f a c e was t h i n n e r than t h e o x i d e s t r i p p e d from t h e f r a c t u r e s u r f a c e o f f u l l y c r a c k e d specimens.  Further evidence  that  t h e o x i d e was t h i n n e r c o u l d be seen b y comparing i n s i t u x - r a y s p e c t r a  - 58 -  F i g . 16.  S o l i d i f i e d c r a c k s o l u t i o n on f r a c t u r e s u r f a c e o f t y p e 304 specimen p a r t i a l l y s t r e s s c o r r o d e d i n b o i l i n g M g C l s o l u t i o n and m e c h a n i c a l l y f r a c t u r e d a t room temperature (800x m a g n i f i c a t i o n ) 2  -  from  fully  cracked CrKa,  cracked type  type  peaks  w e r e o f t h e same r a t i o specimens. of  -  310 s p e c i m e n s  310 s p e c i m e n s .  FeKa, and NiKa  59  I t was  t o those  observed  o b t a i n e d from  t h e x - r a y s were coming from  that  from  sufficiently  cracked surface  mechanically thin  partially  the height of the  the p a r t i a l l y  as peaks o b t a i n e d from  T h u s , t h e o x i d e was  taken  that  the metal substrate.  fractured  the majority  -  4. 4.1  Diffraction Electron  and  60  -  DISCUSSION  Studies  diffraction  p a t t e r n s from  corrosion products, both  s t r i p p e d , were c o n s i s t e n t w i t h a s p i n e l  structure.  agreement w i t h t h e o b s e r v a t i o n s and  predictions  On  lines  some d i f f r a c t i o n  observed  and  M203(either observed  patterns, faint  identified 2  stainless  steels  MgCl2 + F e C l 3 oxychlorides. patterns  3  or possibly  corrosion  in boiling  solutions.  He  lines  lines  they belonged  t o a rhombohedral type  from  304  2  from on  oxides  on  the  The  oxide  patterns,  one  b e l o n g i n g t o a corundum t y p e  belonging  to a spinel.  this  surface.  s t u d y had  and  observed  boiling  Birley's  125°C  or  diffraction  Fe203.  Nielsen  f o r m e d on t h e 3  corrosion  s u r f a c e produced oxide  two  concluded Fe203).  different fracture  distinct  M2O3, a n d  the  type  observed.  o x i d e p a t t e r n on  s.c.c. fracture  structure  i n w h i c h no  This suggests  [14]  exterior  s o l u t i o n s were  stress  only a spinel  In c o n t r a s t , the  [17]  310  other  This i s i n contrast to the observations  a spinel  o x i d e p a t t e r n was  exterior  and  type  products  3  surface.  B a k e r e t a l . [ 1 5 ] who  the  corrosion 304  were  Birley  o x i d e , M203(eg. C r 2 0 ,  from  the oxide  spinel  of the  s p i n e l p a t t e r n s and  s p e c i m e n i n MgCl2 + ' F e C l  patterns taken  exterior  on  Cr 03,  associated with  D i f f r a c t i o n patterns taken of the  to the  them a s b e l o n g i n g t o m a g n e s i u m  observed  associated with  not  from  surfaces of  interpreted  [5,17,14],  chlorides.  154°C MgCl2 s o l u t i o n s  However, t h e  c o u l d a l s o be  fracture  also observed  surface  to metal  i n s p i n e l patterns taken  formed on t h e s t r e s s  of others  related  situ  This i s i n  as p o s s i b l y b e l o n g i n g t o o x i d e s  Cr203 o r F e 0 ) ,  extra lines  not  in  of  the  surface oxide distinct  t h e r e was  a  M2 0  3  difference  in type  -  61 -  between t h e c r a c k environment in  two d i f f e r e n t Nielsen  isolated by  hydrated  stress  oxides  Transformation observed  corrosion  the  hydroxides  t o say they  microscope  would n o t be s t a b l e for boiling on  iron  MgCl2  environments  o f pH  i n the oxides  column.  solutions.  i n solutions  being a spinel  I t was f e l t ,  environments Sato  [30,31].  environment.  during  diffraction  suggested stress of  that  metal  o f such  l o w pH a s r e p o r t e d  that  corrosion  chlorine  were o b s e r v e d grade  could exist  crack environment  peaks  i n the x-ray  s p e c t r a taken  c o u l d be t h e t r a n s f o r m a t i o n o b s e r v e d  corrosion  products  t o an F e C i  from  3  stress  t  corrosion  products  were t a k e n  from  study [5]  i nthe  by t h e presence corrosion  o f a hydrated  metal  b y N i e l s e n [ 1 4 ] ; t h e FeCl2  pattern (Table XII).  corrosion  i nthe  Pourbaix  the stress  The d e h y d r a t i o n  s u r r o u n d i n g metal' and w a s h i n g t h e o x i d e the  from  spinel.  i n the present  was s u p p o r t e d  chloride  similar  exists  as a s t a b l e phase  and t h i s  products.  oxide  2  surface corrosion  being  i n acid  FeCl2'4H 0.  fracture  pattern  films  o n t h e s u r f a c e was a n a n h y d r o u s  o f reagent  chlorides  but i t  hydroxides  et a l . [32] studied passive  Transformations analysis  No  however, t h a t  T h u s , t h e r e i s some d o u b t a s t o w h e t h e r a h y d r a t e d crack  been  t h e s p e c i m e n was i n  o f v a r i o u s pH a n d c o n c l u d e d *5 t h e o x i d e  caused  o f t h e beam.  during this.study,  d i d not occur while  i n s.c.c.  were  i n t h e e l e c t r o n beam h a s  by o t h e r s , t h e end r e s u l t  evacuated  resulting  products  cracks, and s p e c u l a t e d t h e y  l o s i n g water under t h e i n f l u e n c e  of iron  not possible  environment,  transformations i n corrosion  t r a n s f o r m a t i o n s were o b s e r v e d is  solution  oxides.  [14] observed  from  and t h e b u l k  Nielsen  isolated  cracks by d i s s o l v i n g t h e i n methanol.  the fracture  In our study, surface after i t  -  had  been washed i n h o t w a t e r .  isolated  from  cracks would  Therefore,  i t i s more p r o b a b l e  study. iron,  spinel  from  oxide  X-ray  spectroscopy, although  analysis  t h e o x i d e was nickel,  primarily  MgCl  2  effect  fracture MgC'l  2  i n the  that  chlorides  the  of impurities FeCr 0 2  suggests  l t  Hochman's  [18]  metal present  other than corrosion  dispersed in  nickel, product  the  oxide  onthe  + FeCl  stripped spinel  was  3  consistent.  stress  that  spinel. 316  the  corrosion  solution.  (FeC^C^ ) with  oxide  o b s e r v a t i o n s on  steel type  316  showed of  chlorine.  The  and  i n general  i n MgCl  2  single  and  impurities  i s defective were  fracture  Diffraction  corrosion products  These r e s u l t s stainless  It  i s not agreement  solutions crystals  and in  solutions. The  no  on  chromite  N i e l s e n ' s [ 1 4 ] w o r k on  Marek a n d  than  f o r elements  qualitative,  t h e MgCl^  areas  a  trapped  washed f r a c t u r e s u r f a c e s .  molybdenum, magnesium, p h o s p h o r o u s , and  a stoichiometric with  except  of similar  silicon,  presence  analysis  a chromium e n r i c h e d F e - C r  i n a l l cases  and  products  out.  Analysis  surface x-ray  ruled  X-ray  indicated  from  i n N i e l s e n ' s [14] study no  corrosion  a dehydration of a hydrated  c o n t a i n e d some m e t a l be  the  chlorides  molybdenum, t h e p o s s i b i l i t y  cracks cannot  stripped  that  Since N i e l s e n conducted  isolated  4.2  products  observed  chromium, and  that  c o n t a i n more m e t a l  solution  w o u l d be  -  It is likely  solidified  chloride  than  62  addition on  the  of CoCl  structure  surface oxide.  solutions  2  observed  and  HCl  t o the b a s i c  or composition  of the  MgCl  2  solution  stress  Smith, e t a l . [ 9 ] i n s t u d i e s on that  the  pH  inside  the  had  corrosion 4340 s t e e l  crack d i d not  vary,  in  -  being pH  c o n s t a n t l y pH  2-10.  constant  suggest  that the  crack.  Hence, a c i d  expected any of  effect s.c.c.  reduction quite  by  pH  1.2-2.5 i n 304 pH  the  i s not  bulk  environment  surprising  environments.  Although  potential  Fe  than  observed  i s c o n t r o l l e d by  crack  the  was  steel.  observations  conditions within solution  thermodynamics  The  be  absence  of  selectivity Co  has  + 2  of this  chloride  the  would not  or oxide.  from  solution  These  c o n s i d e r i n g the  i n a deoxygenated, high  varied  crack  a t room t e m p e r a t u r e  , the  0  solution  stainless  a d d i t i o n s to the  C0CI2  different  the bulk  Baker e t a l . [15]  crack  to affect  -  3.5-3.9, w h i l e  Similarly  t o have a  63  a  higher  ion could  be  c o n c e n t r a t i o n , low  pH  solution. Addition to  failure  (see  composition a spinel  of FeCl3  approaching  a spinel  The  composition  + FeCl3  solution tip  are  FeCr^^ ferric in  an  produced  nature  Fe3C\ c o m p o s i t i o n an  FeCr 0 2  l t  g r a d i e n t c o u l d be the  same a t t h e  solutions.  composition a t the  composition  e x p l a i n e d by  cases,  the  during electrochemical dissolution ferrous ions  Fe ^, +  and  s p i n e l . However, i n t h e i o n s m i g r a t i n g from  the  tip.  solution  The  reduction of f e r r i c  c o n t a i n i n g both  Fe  + 3  at  and  iron  corrosion product  solution the  that  2  MgCl are  2  .  the  approached  to  c r a c k w a l l s remote  + 2  interface.  and  ions entering  ions to ferrous ions, Fe  suggests  solutions  + FeCl  able  a  interface  the metal  MgCl  time  with  gradient  assuming  only  the  at the propagating  s i t u a t i o n with  the bulk  oxide  solution  crack t i p f o r both  In both  decreased  a layered spinel  of the  c a t h o d i c r e a c t i o n s o c c u r r i n g on  crack a  and  The  approaching  e n v i r o n m e n t was  2  V)  gradient.  and  MgCl  Table  t o t h e b a s i c MgCl2 s o l u t i o n  3  crack an  solutions,  participate from  the  will,yield  Hydrolysis reactions in  -  such  solutions  which  d e p o s i t on  Fe  hydrolysis  2Fe  solution current would  the  lead  reduced  time  environments phases  The  t i p and  pH pH  4.5  4 ^ 0 5 = * FesOi+ ions  c o r r o s i o n was  observed  solutions,  The  f o r the  area  i n the  higher  as  the  MgCl  S.C.C.  environments. i n water at  t i p , and  steels  i t i s not  H o w e v e r , E -pH 150°C a r e M Cl  diagrams  do  as  f o r Fe-FeCl2-H20  i s measured w i t h diagrams  crack  stainless  are  reference .  no  provide  [16,15,9,36].  useful  ( S . H . E . ) f o r 304  and  -0.103V  Under t h e s e  stress  in boiling  154°C  (S.H.E.) f o r  310  crack t i p p o t e n t i a l s ) . shows t h a t t h e . c r a c k  pH  Newburg  b e l o w w h i c h no  steels  predict  for  [31,33],  25°C, and  they  boiling  possible to  available  at  in  been r e p o r t e d t o v a r y between  of the  f o r a l l three alloys.  a  Crack  applied potentials  not  FeCl3  corrosion  crack  diagrams, but  c r a c k s has  diagrams  and  stainless  F i g . 17-20, where E  2  +  2  corrosion current  Therefore,  for austenitic  E -pH  (1+)  +  observed.  austenitic  exist.  i n the bulk  -0.128V  8H  r a t e s at the  Within the  applied potentials,  data with  +  corrosion potential  [35] measured c r i t i c a l  composition  ^  steel-MgCl  inside  Fe^C^  eg;  hydrogen electrode,S.H,E.).These  for stainless  information.  the active  nickel  l t  an  + 2  to f a i l u r e ,  not  [5,34] (see  standard  (these are  2  f o r c h r o m i u m i n w a t e r + 0.1  25°C  Uhlig  do  i n these  chromium, and  1 at the  FeCr 0 .  solution.  2  diagrams  substitute  this  MgCl  -pH  the  approaching  to increased dissolution  are diagrams  2  a higher  Potential  system at  Fe +  + 2  Equilibria  iron,  MgCl  + Fe  + 3  -pH  stable  and  e~ ! = *  Potential  chloride  to  spinels  reduction of ferric  i n the  corresponding  the  +  + 3  should y i e l d than  -  the p r e - e x i s t i n g  reduction  Furthermore,  4.3  could y i e l d  64  Comparing  environment  conditions only  is in a  -  Fig-  1 7  -  65  -  P o t e n t i a l -pH ( E - p H ) d i a g r a m f o r t h e C r - H 0 s y s t e m . o f s o l u b l e s p e c i e s 10 M., from Brook [ 3 3 ] . 2  Concentration  6  Fig.  18.  P o t e n t i a l -pH ( E - p H ) d i a g r a m f o r t h e N i - H 0 o f s o l u b l e s p e c i e s 10 M., f r o m Brook [ 3 3 ] . 2  6  system.  Concentration  -  Fig.  20.  66  -  C a l c u l a t e d a r e a s o f s t a b i l i t y o f F e , F e C l * 4 H 0 , and F e 0 i n the presence o f a s o l u t i o n e l e c t r o n e u t r a l i n F e C l , ( s c h e m a t i c ) from Pourbaix [ 5 ] . 2  2  2  3  [ +  -  chromium h y d r o x i d e would probably  + 2  ,  Ni  +  2  ,  solidified cracked  Cr  + 3  diagrams  ,  crack  and C r  solution  specimens.  potential  corrosion tests  study,  composition the bulk  Nernst  and  present. with  nor  nickel  t o be u n r e s o l v e d .  T h e E -pH  s h o u l d be  of other  ions  activity  of Ni  Wilde  steels  2.303 l o g  steel  + 3  /Cr  ratios  + 2  F i g . 17 b y (aCr  + 3  /aCr  using + 2  )] + o  fraction  chromous  ions  o f Cr ^  2  Staehle  ions  could react  as w e l l as F e C r 0 t j .  diagram  q u i t e low.  (eg. C r , F e 2  + 2  in boiling H i s work  The f a t e  [7] reports that the s u r f a c e , but Wilde  dissolved uniformly, neither enriching the a l l o y  i n d i c a t e s t h a t the a c t i v i t y  potentials  from  d i s s o l v e d from the a l l o y  depleting i t .  water  controlled  i n solution.  The C r  a significant  2  that  partially  were  compared t o t h e  oxide.  I t i s p o s s i b l e that these  preferentially  stainless  ions  i n the  surface of  [20] has performed  i n iron  + RT nF  Q  .494, i n d i c a t i n g  appears  contain  detected  o r chromium i o n s  (S.H.E.) o b t a i n e d  [ E = E  l t  i n c h r o m i u m , w h i c h h e a s s u m e d made up  c h l o r i d e ions t o form C r C l ,  nickel is  equation  2  solution w i l l  on t h e f r a c t u r e  the metal  enriched  FeCr 0  i o n s were  o f 304 a u s t e n i t i c  depleted  a n d -0.128V  Ferrous  however, Wilde  o f the c o r r o s i o n product  -0.103V  are.949  a n d was  the crack  for nickel  s o l u t i o n s and determined  2  showed t h a t t h e s o l u t i o n  the  trapped  No t e s t s  i n this  at  ions.  Consequently,  environment.  indicate  + 2  performed  MgCl  i s stable.  be s t a b l e i n t h i s  T h e s e E -pH Fe  (oxide)  67 -  ,  Cl  of N i  of the nickel  [20] reported surface  o f F i g . 17 f o r p u r e n i c k e l i n +  2  However,  ions  at the  the e f f e c t  ) at high  aforementioned o f the  concentrations  presence on t h e  ionic  i s unknown.  [ 2 0 ] and S t a e h l e ' s  [ 7 ] work, on a u s t e n i t i c  stainless  steels  -  in  chloride  bulk may  specimen be  these  is  very  in  stress  4.4  s u r f a c e s and  fracture  It  that the  was  observed  o f type  stress  fractured  have  the s o l u t i o n  had  does n o t  i n h e r e n t l y form  of  oxide  stripped  of  310  indicated  corrosion  in the  crack.  Hochman this 310 The  metal  oxide oxide  through  on  the  left  a thicker  Similarly,  This suggests  on  and  film of  thickened with  MgCI^  isolated  the  MgClg  304  and  and  solutions  time  oxide  310  left  for  removed  mechanically f o r one  hour  Thus  solution. cracked  i n the  310 Observations  specimens  stress  N i e l s e n [ 1 4 ] , and  were t h i c k e r  dynamic c o n d i t i o n s i n s i d e  on  However,  solution  specimens  bulk  by  on  specimens.  than  i n the  studies  solutions.  than  surfaces of p a r t i a l l y  oxides  pH  s u r f a c e appearance.  oxide  solution  corrosion fracture  316  1 5 4 ° C MgCL^  when  formed  + FeCl^  stress  304  by  the  solutions  used  tip  i n oxides  In the b o i l i n g  fracture  oxide  crack  uniformly thicker  of b o i l i n g  [18], i n b o i l i n g  study.  variation  surface of  fracture  that the  The  i s evidenced  A l s o , specimens  a similar  from  as  a noticeably thicker  presence  solutions  c a r e must be  s u r f a c e s i n MgCl^  o f .304  upon f r a c t u r e .  i n the  the  s p e c i m e n s was  specimens  d i d not  solution  oxide  corrosion fracture  cracked  hours  310  but  propagation.  the bulk  c o r r o s i o n c r a c k s , and  immediately  and  crack  Films  fully  in  to  i n the bulk  of surface properties i n bulk  initiation,  Growth o f Oxide  surface  40  f o r crack  from  -  been performed,  Studies  results  different  exterior  has  surface.  significant  applying  the  solutions  68  than  the  Marek  oxides  crack  cause  to thicken. c o u l d grow b y a porous oxide  general dissolution with resulting  oxide  o f the  underlying  formation.  However,  -  it  i s not l i k e l y  that the oxide  because t h e cracked thicken.  as t h i s  dissolution  p o s s i b l e f o r hydrogen  the  oxide  the  fracture  other and  crack The  ions  i s conductive. surface oxide  limited  solution,  presence  significant  [ 5 ] , and then  oxide  t o be porous.  contain pores,  metal  interface.  which  allow  The h y d r o g e n  + 2Cr  + 3  + 4 H 0 Z=± 2  spinels  the crack.  to break and  i n boiling  316 t a k e  occurs, cracks  film.  and  approximately  i t suggests  Fe  ions  form  result  in a  i t i s possible for at the crack the oxide on t h e  (5)  +  the present  observations of  o f others  (5) t o the r i g h t  Specimens  o f 310 t a k e  solutions,  2-4 h o u r s .  observed.  i n the oxide.  t i p ; eg.  r e d u c t i o n o f hydrogen  2  ions  within the  t o be r e d u c e d  while  o f l o w pH ions  on t h e  and cause f u r t h e r  approximately specimens  I f a process  that the corrosion products  i n 310 s p e c i m e n s a s  will  + 2  Furthermore,  and t h e o b s e r v a t i o n  154° C M g C l  are present  a t the crack + 8H  both  crack w a l l s would d i s p l a c e equation growth o f t h e s p i n e l  ferrous  could arise.from the hydrolysis  F e C r ^  Consequently,  Since  chlorides,  hydrogen  ions  (5) i s c o n s i s t e n t with  but contained  t h e crack has propagated,  i o n s produced by d i s s o l u t i o n  chromium e n r i c h e d within  I f metal  dissolve after  could  Equation  + 3  increase i n c o n d u c t i v i t y [37].  tip  + 2  Fe  However,  t o be p r e s e n t  3  crack  Fe  ions  i t i s p o s s i b l e f o r some F e 0 ^  the  of metal  the conductivity.  o f s m a l l amounts o f b o t h  t i p , then i t  conductor.  chromite,  of ferric  crack  o f s.c.c.  on t h e c r a c k w a l l s , p r o v i d i n g  i s n o t a good  was n o t t o t a l l y  concentrations  d i d not  o f t h e c r a c k w a l l s w o u l d n o t be  t o be r e d u c e d  Chromite  dissolution  f o r 40 h o u r s  a r e c a t h o d i c t o an a n o d i c  e l e m e n t s w h i c h may m o d i f y  very  i n solution  would l e a d t o crack b l u n t i n g and absence  Assume t h e c r a c k w a l l s is  thickened by u n d e r l y i n g metal  s a m p l e o f 304 l e f t  Also, anodic  anticipated  69 -  similar  40 h o u r s  o f 304 t o t h e above  would be t h i c k e r  i n the s.c.c.  -  4.5  70  -  E n v i s i o n e d Events w i t h i n the S t r e s s C o r r o s i o n Crack The r e s u l t s o f t h i s s t u d y were c o n s i s t e n t w i t h an e l e c t r o c h e m i c a l  mechanism o f s . c . c , whereby t h e c r a c k advanced by a n o d i c  dissolution  o f the c r a c k t i p f o l l o w e d by p r e c i p i t a t i o n o f the c o r r o s i o n on the w a l l s o f t h e c r a c k . prevented to  P r e c i p i t a t i o n of the c o r r o s i o n  l a t e r a l a t t a c k o f the c r a c k w a l l s and l o c a l i z e d  products products  dissolution  the c r a c k t i p . H y d r o l y s i s o f a n o d i c a l l y d i s s o l v e d m e t a l i o n s (see e q u a t i o n  gave r i s e t o t h e o b s e r v e d s p i n e l c o r r o s i o n p r o d u c t hydrogen i o n c o n c e n t r a t i o n w i t h i n the c r a c k .  and i n c r e a s e d  Reduction  Thus t h e r e was  the  o f the hydrogen  i o n s on the c r a c k w a l l s p r o v i d e d the c a t h o d i c r e a c t i o n n e c e s s a r y maintenance o f a n o d i c d i s s o l u t i o n .  5)  for  an a u t o c a t a l y t i c  r e a c t i o n w i t h i n the c r a c k . [The r o l e o f s t r e s s c o u l d be c o n f i n e d t o t h e r u p t u r e o f any  c o r r o s i o n product  t h e c r a c k t i p and p r e v e n t The  ( f i l m ) which tends t o b l o c k  exposure t o the  environment].  e n v i s i o n e d p r o c e s s r e q u i r e s the c o r r o s i o n p r o d u c t  t o be  c o n d u c t i n g , as i t has t o f u n c t i o n as the cathode f o r the a n o d i c tip.  I t c o u l d be c o n d u c t i v e  electrically crack  e i t h e r because i t i s a n o n - s t o i c h i o m e t r i c  s p i n e l , or because p o r o s i t y i n the f i l m exposes the u n d e r l y i n g  metal.  P o r o s i t y c o u l d a r i s e from c o n j o i n t p r e c i p i t a t i o n o f m e t a l c h l o r i d e s and s p i n e l s , f o l l o w e d by d i s s o l u t i o n o f the m e t a l c h l o r i d e s a f t e r t h e c r a c k t i p had advanced.  The p o s s i b i l i t y t h a t m e t a l c h l o r i d e s are formed  a t the c r a c k t i p has been proposed by Beck [ 3 8 ] .  Working w i t h t i t a n i u m  a l l o y s , Beck proposed t h a t an o x i d e c o u l d not form f a s t enough t o e x p l a i n the current time behaviour The  he o b s e r v e d , whereas a m e t a l c h l o r i d e c o u l d .  f o r m a t i o n o f a s p i n e l u n i t c e l l r e q u i r e s 56 atoms.  Thus, a u n i t c e l l  -  of  FeC^O^would  sheaths ions it  a r e surrounded by a h i g h  chlorides  may  Effect  that  product  formation  a n d 16 c h r o m i c  and form  of Alloy no  cracking.  reaction  evidence  to support  product  film  was  composition  structure,  of nickel  on t h e s t r e s s explained.  stainless  steels  Additions  o f a few p e r c e n t  susceptible  are resistant  to s.c.c.  explain  the variation,  content  current  on t h e d i s s o l u t i o n  density,  Shibata I  max  metal  oxide  formation.  increasing  the  energy  [4].  iron  paths.  of iron  for dissolution  equally  Certainly  and chromium  stainless  greater  Crystal  stainless  steels  than  structure will  [7] studied  ferritic  increased  20 wt  %  alone  cannot  corrode [36].  the e f f e c t  of  nickel  in boiling  dissolution  electrode  Staehle  environments.  steels,  stress  chromium a l l o y s  straining  content.  kinetics,  e n e r g y were  a n d T a k e y a m a , f o u n d t h e maximum  nickel  corrosion  c r a c k i n g b e h a v i o u r has y e t  of nickel  during  corrosion  Consequently,  i n stress  austenitic  [40] and S t a e h l e kinetics  in  i n h o t aqueous c h l o r i d e  renders  again  , observed  decreased with activation  to s.c.c.  as f e r r i t i c  a n d Takeyama  MgCl^ s o l u t i o n s .  than  variation  fault  fracture  corrosion  Additions  i n resistance t o s.c.c.  Shibata  Therefore,  on e l e c t r o c h e m i c a l  Nickel-free,  nickel  results  factor  and s t a c k i n g  the  very  ions.  composition.  not the only  of alloy  dislocation  be s a t i s f a c t o r i l y  kinetics  i n alloy  as i s e v i d e n t by t h e d i f f e r e n t  to  Meanwhile, the metal  and/or hydrated  a consistent  important, effect  solvation  Composition  The e f f e c t s  crack path,  in their  of chloride  of metal chlorides  composition with v a r i a t i o n  corrosion  ions  the oxide.  concentration  h a v e more f a v o u r a b l e  T h e r e was  the  8 ferrous  t o come t o g e t h e r , r e a c t  i s possible  4.6  require  71 -  experiments,  [7] observed  as t h e n i c k e l  that  content  -  72  -  i n c r e a s e d , l e a d i n g t o a decrease i n d i s s o l u t i o n c u r r e n t .  Shibata  and Takeyama a l s o found t h a t t h e c u r r e n t d e n s i t y decay d l / d T i s more r a p i d f o r 304 than 310. higher f i l m formation  They i n t e r p r e t e d t h i s as meaning 304 had a  ( r e p a s s i v a t i o n ) r a t e t h a n 310.  I f 304 does  r e p a s s i v a t e f a s t e r i t means t h e r e c o u l d be more g e n e r a l c o r r o s i o n a t t h e crack t i p i n 310 a l l o y s , t h e r e b y b l u n t i n g t h e c r a c k and l o w e r i n g t h e s t r e s s i n t e n s i t y at the crack t i p . An a l t e r n a t i v e and i m p o r t a n t e f f e c t o f t h e n i c k e l c o m p o s i t i o n may be t h r o u g h i t s e f f e c t on the r e v e r s i b l e , e l e c t r o d e p o t e n t i a l , E , Q  of the bare a l l o y surface.  N i c k e l has been n o t e d t o r a i s e b o t h  the c r i t i c a l p o t e n t i a l f o r s . c . c . and t h e c o r r o s i o n p o t e n t i a l [ 1 3 , 3 5 ] . A higher corrosion p o t e n t i a l , E , could l e a d t o a reduced c o r r o s i o n . corr &  current, I  c  corr  , and a r e d u c e d r a t e o f m e t a l d i s s o l u t i o n a t t h e a n o d i c a l l y  propagating crack t i p .  J  T h i s i s most e a s i l y v i s u a l i z e d w i t h  t o an Evans diagram [ 4 1 ] , as shown i n F i g . 21.  respect  -  73  -  X LU  . o  < IZ  o  Ul  Ul  \—  o OL  CURRENT—  Fig.  21«  (log scale)  Schematic Evans diagram showing p o s s i b l e e f f e c t s of a l l o y i n g on e l e c t r o c h e m i c a l b e h a v i o u r . Base a l l o y has e l e c t r o c h e m i c a l b e h a v i o u r d e p i c t e d by c u r v e s a and c . Upon a l l o y i n g w i t h n i c k e l , the a i l o y r e v e r s i b l e p o t e n t i a l increases from E to E ', Q  resulting  t o I' . Alloying corr corr may l o w e r t h e e x c h a n g e c u r r e n t d e n s i t y f o r h y d r o g e n r e d u c t i o n from I to I' , again, lowering I to I' [39]. ° ° corr corr n  i n a lower c o r r o s i o n current  0  I  .5.  Electron  CONCLUSIONS  d i f f r a c t i o n and q u a l i t a t i v e x - r a y a n a l y s i s  p r o d u c t s formed i n s t r e s s c o r r o s i o n s t e e l s 304, 316, and 310 t e s t e d the f o l l o w i n g . 1)  of corrosion  cracks of the a u s t e n i t i c  stainless  i n b o i l i n g aqueous MgCl2 s o l u t i o n s  l e d to  conclusions;  The c o r r o s i o n  p r o d u c t on t h e s t r e s s c o r r o s i o n  fracture  of t h e d i f f e r e n t a l l o y s was s i m i l a r , b e i n g a chromium e n r i c h e d oxide containing  surface spinel  l e s s e r amounts o f t h e elements i r o n , n i c k e l , molybdenum,  s i l i c o n , phosphorous, magnesium, and c h l o r i n e . 2)  There was a s i g n i f i c a n t d i f f e r e n c e  between t h e o x i d e (and  e n v i r o n m e n t ) on t h e e x t e r i o r specimen n o t c h s u r f a c e , (and  environment) i n the s t r e s s c o r r o s i o n 3)  crack.  The p r e s e n c e o f s p i n e l o x i d e was c o n s i s t e n t  of o t h e r s on t h e pH and e l e c t r o c h e m i c a l p o t e n t i a l cracks i n a u s t e n i t i c s t a i n l e s s s t e e l s .  and t h e o x i d e  with the observations  (E) o f s t r e s s  corrosion  These r e s u l t s i n d i c a t e t h e c r a c k  environment was i n t h e l o w pH " a c t i v e t r i a n g l e " r e g i o n o f t h e E-pH d i a g r a m s for the a l l o y s . 4)  The v a r i a t i o n i n s . c . c . b e h a v i o u r between t h e d i f f e r e n t a l l o y s  c o u l d n o t be a d e q u a t e l y a c c o u n t e d f o r i n terms o f t h e c o m p o s i t i o n o f t h e oxide.  -  75 -  BIBLIOGRAPHY ENGELL, H . J . T h e o r y o f S t r e s s Nato  Scientific  S T A E H L E , R.W.  Affairs  Corrosion Cracking i nAlloys,  Division  Fundamental Aspects  P. 3, P r o c e e d i n g s Association  (1971)..  o f Stress  o f Conference,  Corrosion Cracking,  p u b l i s h e d by N a t i o n a l  o f Corrosion Engineers  (1969).  N I E L S E N , N.A.  C o r r o s i o n , V o l . 2 7 , #5, P. 173 ( 1 9 7 1 ) .  S T A E H L E , R.W.  Fundamental Aspects  P. 2 1 4 , P r o c e e d i n g s Association POURBAIX, M. Nato  o f Stress  o f Conference,  o f Corrosion Engineers  Theory  Scientific  o f Stress Affairs  Corrosion Cracking,  published by National (1969).  Corrosion Cracking i nAlloys,  Division  P. 8 6 ,  P. 1 7 ,  (1971).  BOND, A . P . a n d DUNDAS, H . J . C o r r o s i o n , V o l . 2 4 , #10, P. 344 S T A E H L E , R.W.  Theory  Nato S c i e n t i f i c  o f Stress  Affairs  Corrosion Cracking i nAlloys,  Division  MCCARTHY, H.A. a n d HARRISON, P . L .  (1968). P. 2 2 3 ,  (1971).  C o r r o s i o n S c i e n c e , V o l . 14,  P. 469 ( 1 9 7 4 ) . SMITH, J . 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Applications,  Scientific  Edward A r n o l d L t d .  -  78  -  APPENDIX A This Analysis surface  appendix contains the  oxides  are  presented  the  diffraction  p a t t e r n s are  by  The  summarized  of representative diffraction  (from which  films  data  lattice  as  are  used  parameters  indices  from  appencix  - Miller  K  - camera c o n s t a n t  (see page  D  - diameter  electron  pattern, d  the  v  M a  rise  relative slope  o  of  interplanar  rive I  of crystal  units  to  2  38)  ring  t  k  units  of  ins-A  ring  (h  + l )" 2  D.  2  + k  2  +  The  microscope.  0  on  the  to plane  units  of diffraction 2  of D vs  2  (h  planes  of  diffraction  5  crystal  where a  o  =  as K/M  £hklj  which  Angstroms  ring  + l ) d e t e r m i n e d by  2  parameter of c u b i t + k  o f D vs  fracture  c o r r o s i o n product  corresponding  lattice  2  various  as f o l l o w s ;  lattice  intensity  (h  stripped  are  X.  X were d e t e r m i n e d ) .  diffraction  diffraction  o f D vs  the  and  inches  spacing  visual  VI  transmission electron  hkl  of the  p a t t e r n s from  i n Table  a l l taken  in this  Tables  graphical plots  c o n v e n t i o n a l means i n t h e symbols  by  least  obtained  squares f i t  from  plots  l  2  )  - 79  Table  Al.  304 S.C.C. i n M g C l Solution pattern  -  , Oxide  2  #22217  line  Stripped with  camera  Din.  dA°  constant  I  0.39 0.63 0.74 0.77  2.54 2.44  5  0.835  2.25  W W S WW VW  6 7  0.90 0.98  WW WW  4.82 2.98  s  Bromine-Methanol  K = 1.88  FeCr20i (hkl)  V 1 2 3 4  1%  222 —  3.46 _  400 331  4.0 4.36  1.05  1.68 1.62 1.47 1.41  WW  422 333/511 440 531  1.385 1.47  1.36 1.28  Dots VW  620 533  15  1.555 . 1.59  1.21 1.18  W  444 551/711  Data p l o t t e d Slope  M = K  a  0  i n F i g . A l ,D vs ( h = 0.225 i n  = 1.88  A  0  0.225 Lattice  parameter  a  = D  8.36A°  -  Dots  2  + k  2  2  1.73 2.83 3.32  1.115 1.16 1.275 1.33  16  + k  111 220 311  9 10 11 12 13 14  WW M S  Jh  z  +  2.09 1.92 1.79  8  ins-A°  + l  —  2  )  4.9 5.2 5.66 5.92 6.32 6.56 6.93 7.14  +l  2  80  -  -  (h *  k*  r  Fig. A l .  2  I*)?  P l o t o f D vs ( h + k + .1 )' from T a b l e A l . D i f f r a c t i o n p a t t e r n #22217, 304 s . c . c . i n M g C l , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n 2  2  2  2  2  - 81 -  Table A2.  304 S.C.C. i n M g C l , Oxide S t r i p p e d w i t h 1% Bromine-Methanol Solution p a t t e r n #23299 camera c o n s t a n t K - 1.95 ins-A° 2  line  Din.  dA°  I  FeCr 0i 2  \r V  1 2 3 4 5 6 7 8 9  0.79 0.82 0.93 1.32 1.53 1.61 1.86 2.00 2.10  Slope  M = K  a  311 222 400 440 533 444 800 555/751 840  2.38  2.10 1.48 1.27 1,21 1,05 0.975 0.93  = 0.232 i n  = 1.95 A° 0.232 L a t t i c e parameter a Q  0  = 8.41A°  2  + k  2  (hkl)  2.47  Data p l o t t e d i n F i g . A2, D vs ( h  J h  +  2  + k  2  + 1 ) 2  %  3.32 3.46 4.0 5.66 6.56 6.93 8.00 8.66 8.94  + l  2  - 82  Fig.  A2.  Plot  o f D vs  (h  2  -  + k  2  +.1 ) 2  2  from Table  A2.  p a t t e r n #23299, 304 s . c . c . i n M g C l , o x i d e bromine-methanol s o l u t i o n . 2  Diffraction stripped  with  1%  - 83 -  T a b l e A3.  304- S.C.C. i n M g C l , Oxide S t r i p p e d w i t h 1% Bromine-Methanol Solution p a t t e r n #23389 camera c o n s t a n t K = 1.88 ins'A° 2  line  D in.  dA°  I  FeCr 0i (hkl) 2  V  1 2 3 4 5 6 7 8 9 10 11 12  0.39 0.63 0.75 0.90 1.05 1.1 1.17 1,28 1.47 1,55 1,72 1.80  4.90 3,03 2.55 2.12 1,82 1,71+  1.63 , 1,49 1.30 1,23 1,11 1.06  W M S M WW WW W M W W W W  111 220 311 400 -  422 511/333 440 533 444 553/731 800  Data p l o t t e d i n F i g . A 3 , D vs ( h + k 2  Slope  M = K  a  Q  = 0.224 i n  = 1.88 A 0.224  0  L a t t i c e parameter a  D  = 8.39 A°  +  2  + l )* 2  5  Jh  2  + k  2  1.73 2.83 3.32 4.0 4.9 5.2 5.66 6.56 6.93 7.68 8.0  + l  2  - 85 -  Table A4.  304 S.C.C. i n M g C l Methanol S o l u t i o n p a t t e r n #23462  D in.  line  2  + C o C l , Oxide S t r i p p e d 2  camera c o n s t a n t K = 1.84 ins*A°  dA°  I  FeCr20it  V  1 2 3 4 5 6 7 8 9 10 11 12  0.375 0.61 0.72 0.87 1.12 1.22 1.29 1.42 1.50 1.55 1.66 1.73  4,-91 3.02 2.55 2.12 1.64 1.51 1.43 1.30 1.23 1.19 1.11 1.06  M W S S WM M VW VW W VW VW VW  a  Q  = 0.216  = 1.84 A° 0.216  L a t t i c e parameter a  c  = 8.52 A  0  2  + k  111 220 311 400 511/333 440  1.73 2.83 3.32 4 5.2 5.66  444 711/551 553/731 800  6.56 6.93 7.14 7.6 8.0  533  2  M = K  Jh  (hkl)  Data p l o t t e d i n F i g . A4, D vs ( h + k Slope  i n 1% Bromine-  2  +  l  2  ) ^  _  2  + l  2  - 86  Fig-  A4.  Plot  o f D vs  (h  2  -  + k  2  + l  2  ) ^ from Table  p a t t e r n #23462, 304 s . c . c . i n M g C l w i t h 1% b r o m i n e - m e t h a n o l s o l u t i o n .  2  A4.  + CoCl , 2  Diffraction oxide  stripped  - 87 ~  •  T a b l e  A 5  -  3  S.C.C. i n MgCl Methanol S o l u t i o n p a t t e r n #23459  + C o C l , O x i d e . S t r i p p e d i n 1% Bromine-  line  dA°  0  4  2  2  camera c o n s t a n t K = 1.84 ins*A°  D in.  . I  FeCr 0it (hkl) 2  V  1 2 3 4 5 6 7 8 9 10 11 12  0.38 0.62 0.72 0.87 0.95 1.08 1.12 1.22 1.29 1,43 1.50 1.55  4,-84 2.97 2,55 2.12 1.94 1.70 1.64 1,-51 1,43 1,29 1,23 1.19  M w S M WW VW M W VW WW WW WW  111 220 311 400 331 422 511/333 400 _  533 444 711/551  Data p l o t t e d i n F i g . A5, D v s ( h + k 2  Slope  M = K = 0.216 i n a ;•= 1.84 A 0.216  0  n  L a t t i c e parameter a  Q  = 8.52 A  0  2  + l )^ 2  Jh* + k^+ I 1.73 2.83 3.32 . 4 4.36 4.90 5.2 5.66 6.56 6.93 7.14  1  - 88  Fig-  A5,  Plot  o f D vs ( h  2  + k  2  + l  2  ) ^ from  p a t t e r n #23459, 304 s . c . c . i n M g C l w i t h 1% b r o m i n e - m e t h a n o l s o l u t i o n .  Table 2  A5.  Diffraction  + C0CI2, oxide  stripped  89  Table  A6.  304 S.C.C. I n M g C l Methanol Solution pattern  line  0.38 0.61 0.72  4 5  0.75 0.81  6 7 8  0.85 0.94 1.06 1.13 1.23  Oxide  2  #23464  1 2 3  12 13 14 15  + CoCl ,  2  camera  Din.  9 10 11  -  dA°  4.74 2.95 2.50 2.40 2.22  1.29 1.36 1.42  2.12 1.92 1.70 1.60 1.46 1.40 1,32 1,27  1.49 1.54  1.21 1.17  Stripped  constant  I  K = 1.80  V  FeCr 0 (hki)  M W-M S  111 220 311  2  w  with  H  -  M W W W-M W-M  400 331 422 511/333  WW W W VW  620 533  440 531  w  444 711  ins«A°  Jh  Z  + k  2  + I  2  H  222  WW  1% B r  1.73 2.83 3.32 3.46  -  4 4.36 4.90 5.2 5.66 5.92 6.32 6.56 6.93 7.14  .  Data p l o t t e d Slope  i n F i g . A6, D vs ( h  M = K  a  Q  =  = 0.216 i n  -1.80  A  0  0.216 Lattice  parameter  a  G  = 8.33  A  0  2  + k  2  + l  2  ) "  - . 90 -  -  T a b l e A7.  91  304- S.C.C. i n M g C l Methanol S o l u t i o n p a t t e r n #23452  line  + H C l , Oxide  2  Di n .  -  camera  dA°  Stripped  constant  0.39 0.44 0.64  M WW M  6  0.75 0.90 1.00  4.90 4.34 2.98 2.55 2.12 1.9.  7 8 9  1.11 1.18 1.28  10 11 12 13 14  Lattice  111  ins«A°  Jh  + k  z  1.73  -  -  S M WW  2.83 3.32 4.0 4,36  1.72 1.62 1.49  W M M  422 511/333 440  4.9 5.2 5.66  1.34 1.44 1.49  1.42 1.33 1.28  VW VW  1.57 1.62  1,22 1.18  = 1.91 A 0.227 parameter  0  a  Q  = 8.41 A °  -  620 533  W W VW  S l o p e M = K = 0.227 i n  0  K = 1.91  Bromine-  220 311 400 331  Data p l o t t e d i n F i g . A7, D vs ( h  a  1%  FeCr20i+ (hkl)  I V  1 2 3 4 5  with  444 711/551  2  + k  2  +  l*)*  5  6.32 6.56 6.93 7.1,  z  +l  2  - '92' -  bromine-methanol s o l u t i o n  -  Table  A8.  -93 -  304 S.C.C. i n M g C l Methanol S o l u t i o n p a t t e r n #23434  line  Di n .  1 2 3 4 5 6 7 8 9 10 11  2  + H C l , Oxide camera  dA°  0.39 0.64 0.76 0.91 1.11 1.18 1.29 1.44 1.48 1.57 1.61  4.90 2.98 2.51 2.10 1.72 1.62 1.48 1,33 1,29 1,22 1.19  I  Stripped  constant  K = 1.91  a  D  111 220 311 400 422 511/333 440 620 533 444 711/551  M M VS  s w M M VW W W VW  2  + k  2  +l  2  ) "  o  = 1.91  A°  0.226 Lattice  parameter a  Q  = 8.45  Bromine-  ins-A°  2  + k 2 3-1*  (hkl)  S l o p e M = K = 0.226 i n a  1%  k  FeCraO^  V  D a t a p l o t t e d i n F i g . A8, D v s ( h  with  A°  i  1.73 2.83 3.32 4.0 4.9 5.2 5.66 6.32 6.56 6.93 7.14  -  94  -  (h*-> k * I )i 2  2  Fig.  A8.  Plot  o f D vs ( h  2  + k  2  + l  2  ) ' from 5  Table  I Asj.  Diffraction  p a t t e r n #23434, 304 s . c . c . i n M g C l 2 + H C l , ' o x i d e 1% b r o m i n e - m e t h a n o l s o l u t i o n .  stripped  with  -  Table  A9.  95  304 S.C.C. i n M g C l Methanol S o l u t i o n pattern  ' line  _  + H C l , Oxide  2  #23436  camera  Din.  dA°  Stripped with  constant  I  1 2 3  0.39 0.51 0.63  4.90 3,75 3.03  4 5  0.75 0.90 1.10 1.18 1.28  2.55 2.12 1,74  6 7 8 9 10 11 12 13  1.34 1.43 1.48  .  1.42 1,34 1,29 1,22 1.19  1.56 1.61  Data p l o t t e d Slope  1,62 1.49  a  0  -  s vs s  220 311 400 422  M  s s w  511/333 440 531  VW  620 533 444  w w  VW  o A  0  0.226 Lattice  111  .  i n F i g . A9, D vs ( h  = 1.91  parameter  a  Q  0i+  = 8.45 A °  Bromine-  ins-A  0  Jh  z  + k  (hkl)  M WW  M = K = 0.226 i n a  K = 1.91  FeCr  V  1%  2  711/551  + k  2  + l  2  ) "  1.73 —  2.83 3.32 4.0 4.9 5.2 5.66 5.92 6.32 6.56 6.93 7.14  2  +l  2  96  ~  Fig.  A9.  _  P l o t o f D vs ( h + k + l ) ^ from Table #23436, 304 s . c . c . i n MgCl2 + H C l , o x i d e bromine-methanol s o l u t i o n . 2  2  2  A9. Diffraction pattern s t r i p p e d w i t h 1%  -  .Table  A10.  97  -  304 S.C.C. i n M g C l 2 ' + • F e C l 3 , O x i d e Methanol S o l u t i o n pattern  . line  #23580  camera  D in.  dA°  Stripped with  constant  I  FeCr 04 (hkl) 2  V 1 2 3 4 5 6 7 8 9 10 11 12 13 14  0.385 0.445 0.63 0.75 0.90 0.99  3.02 2.5 3 2.11 1.92  1.09 1.16 1.26  1.74 1.64 1.51  1.32 1.41 1.47  1.44 1.35  4.94 4.28  1.29 1.23 1.19  1.55 1.60  Data p l o t t e d  M  a  c  o  = 1.90 A ° 0.223  Lattice  parameter  a  Q  = 8.52 A °  +  2  3.32 4.0 4.36  444 551/711  2  c/hJt k  2.83  422 333/511 440 531 620 533  + k  ins«A°  _  220 311 400 331  z  Bromine-  1.73  -  VW VW W VW VW  S l o p e M = K = 0.223 i n a  111  WW M S M WW W M M  i n F i g . A 1 0 , D v s (h  K •= 1.90  1%  l )^ 2  4.90 5.20 5.66 5.92 6.32 6.56 6.93 7.14  + l  2  98 -  -  Table A l l .  99  304 S.C.C. I n M g C l Methanol S o l u t i o n pattern  line  6 7 8 9 10 11 12 13  + FeCl  #23579  3  , Oxide  camera  Din.  1 2 3 4 5  2  -  dA°  I  constant  k  Bromine-  ins«A°  Jh  2  + k  (hkl)  4.87 4.32  M WW  0.515  3.70  W  -  0.635 0.71  2.99 2.68  M W  220  2.83  0.75 0.86 0.90 1.03  2.53 2.21 2.11 1.85 1.73 1.62  S W M WW W M M VW  311  3.32  1.27  1.50 1.43  14 15  1.47  1.29  VW W  16 17  1.56 1.61  1,22 1.18  VW VW  1.33  Data p l o t t e d i n F i g . A l l , D vs ( h M:=  K a  Q  = 0.225 i n  o  = 1.90  A  0  0.225 Lattice  2  1%  0.39 0.44  1.1 1.17  a  with  K = 1.90  FeCv 0  V  •1.33 :1.43  Slope  Stripped  parameter  a  Q  = 8.44 A °  111  1.73  -  -  —  -  _  -  -  400  4.0  422 511/333  4.9 5.2  440 531  5.66 5.92 6.32  -  -  620 533 444  6.56 6.93  711/551  2  + k  2  +l  2  ) ^  7.14  2  +l  2  - 100  Fig.  A l l .  -  P l o t o f D vs ( h + k + l ) " from Table A l l . D i f f r a c t i o n p a t t e r n #23579, 304 s . c . c . i n M g C l 2 + F e C l 3 , o x i d e s t r i p p e d w i t h 1% b r o m i n e - m e t h a n o l s o l u t i o n . 2  2  2  5  _ 101 _  Table  A12.  304 S.C.C. i n M g C l Methanol S o l u t i o n p a t t e r n #23581  line  1 2 3 4 5 6 7 8 9  Di n .  1.27 1.46 1.57  Slope  , Oxide  I  4.87 3.02 2.53 2.11 1.73  0.75 0190 1.1 1.17  3  camera  dA°  0.39 0.63  Data p l o t t e d  + FeCl  2  constant  Lattice  0  2  1.62  M  1.50 1.30  M-S VW  333/511 440 533  1.21  VW  444  = 1.90 A ° 0.225 a  Q  = 8.44 A °  2  + l  ins«A°  + k  1.73 2.83 3.32 4.0 4.9  400 422  + k  Bromine-  2  111 220 311  z  1%  fh  H  W M S M VW  i n F i g . A12, D vs ( h  parameter  with  K = 1.90  FeCr 0 (hkl)  V  M = K = 0.225 i n  a  Stripped  2  )  5.2 5.66 6.56 6.93  2  +l  2  - 102 -  Fig.  A12.  Plot  o f D vs  pattern with  (h  #23581,  2  + k  2  + l  2  304 s . c . c .  1% b r o m i n e - m e t h a n o l  ) ^ from  Table  A12.  i n MgCl2 + F e C l 3 ,  solution.  Diffraction oxide  stripped  - 103 -  Table  A13.  316 S.C.C. i n M g C l , Solution  Oxide Stripped  2  pattern  line  D  #23333  in.  camera  dA°  with  constant  1%  K = 1.93  FeCr20  I  V  0.39 0.65 0.76  4.95 2,97 2.54  W M S  111 220 311  4 5 6  0.92 1.00 1.12 1.2 1.3 1.36  2.10 1.93 1.72  M WW W  400 331  1.61 1.48 1.42  M M  1.46 1,51 1.60 1.64  1,32 1,28  10 11 12 13  1,21 1.18  WW WW M W W  H  422 511/333 440 531 620 533 444 711/551  Data p l o t t e d  i n F i g . A 1 3 , D v s (h2 + k 2 + 1 2 ) ^  Slope M = K  = 0.231 i n  a  a  Lattice  0  o  = 1.93 0.231  A  0  parameter a  0  = 8.36 A °  .  ins-A°  /h^Vk +I . r  (hkl)  1 2 3  7 8 9  Bromine-Methanol  '  1.73 2.83 3.32 4.00 4.36 4.90 5.20 5.66 '5.92 6.32 6.56 6.93 7.14  2  - 104  Fig.  A13.  Plot  o f D vs  pattern  (h  2  -  + k  #23333, 316  bromine-methanol  2  + l  2  s.c.c.  solution.  )  2  from  Table  A13.  i n MgCl2, o x i d e  Diffraction  stripped  with  1%  _ 105 _  Table  A14.  316 S.C.C. i n M g C l , Solution 2  pattern  line  1 2 3 4 5 6 7 8 9 10 11 12 13 14  #23329  D in  4.8 4.17  0.65 0.76 0.92 1.01 1.125 1.2 1.31  2.95 2.53 2.09 1,91 1.71  1.36  1,60 1,47 1.41  1.46 1.51 1.59 1.64  1,32 1,27 1.21 1.17  a  a = Q  Lattice  I  0.40 0.46  M = K  Stripped  camera  dA°  Data p l o t t e d Slope  Oxide  constant  Bromine-Methanol  K = 1.92  2  M WW M VS S  H  111  ins*A°  Jh  2  + k  2  1.73  -  220 311 400 331 422 333/511  4.36 4.90 5.20  M M VW W VW  440 531  5.66 5.92  620 533 444  6.32 6.56 6.93  VW  551/711  7.14  WW W M  z  = 0.230 i n  o  1.92 A ° 0.230  Q  1%  FeCr 0 (hkl)  V  i n F i g . A 1 4 , D v s (h  parameter a  with  = 8.35 A °  + k  2  +l  2  ) "  2.83 3.32 4.0  + l  2  - 106  Fig.  A14.  -  P l o t o f D vs ( h + k + l )^ #23329, 316 s . c . c . i n M g C l 2 , methanol s o l u t i o n . 2  2  2  f r o m T a b l e A14. Diffraction pattern o x i d e s t r i p p e d w i t h 1% b r o m i n e -  - 107 -  Table  A15.  316 S.C.C. i n M g C l , Solution p a t t e r n #22222 2  line  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16  Oxide  camera  dA°  D in.  0.39 0.43 0.53 0.64 0.70 0.76 0.865 0.905 1.04 1.115 1.18 1.285 1.32 1.48 1.52 1.57  Stripped with  I  4.90 4,44 3.60 2,98 2.73 2.51 2.21 2.11 1,83 1.71 1,52 1,49 1,45 1.29 1.26 1.21  constant  K = 1.91 i n s - A  FeCr 0i 2  V  M  2.83  S  311  -  3.32  -  4.0  WW WW W WW VW w. s VW WW WW VW  = 1.91 A °  .230 parameter a  0  = 8.30  A°  -  -  -  422 333/511 400 620 533 444  2  o  -  400  = 0.230 i n  Lattice  2  220  VW VW  Slope M = K  0  + k  1.73  111  M  i n F i g . A15, D vs ( h + k  a  Jh  2  +  0  (hkl)  Tata plotted  a  1% B r o m i n e - M e t h a n o l  2  +  l )^ 2  -  4.90 5.20 5.66 6.32 6.56 6.93  •+ l  2  ,  108  - 109  Table.A16.  316 S.C.C. i n M g C l Methanol S o l u t i o n p a t t e r n #23406  -  + H C l , Oxide  2  Stripped  camera c o n s t a n t  with  K = 1.91  1%  Bromine-  ins«A  0  *•  line  Di n .  dA°  I  1 2 3 4 5 6 7 8  Jh  2  FeCr 0Lt 2  V 0.395 0.46 0.525 0.56 0.64  4.84 4.15 3.64 3.41 2.98  M WW M WW M  0.705  k  +  2  (hkl) 111  1.73  -  -  220  2.83  -  -  -  2.71 2.51 2.18  M S M  9 10 11 12 13  0.76 0.875 0.91 1.01 1.05 1.12 1.18  2.10 1.89 1.82 1.71 1,62  M WW W W M  422 511/333  4.90 5.20  14  1.29  1.48  M  440  5.66  Data p l o t t e d Slope  i n F i g . A16, D vs ( h  M = K = 0.226 i n  a  Lattice  0  = 1.91 A° 0.226 parameter  a  0  = 8.45 A °  311  3.32  -  -  400 331  4.0 4.36  -  -  2  + k  2  + l  2  )'  +  I  2  - no  Fig.  A16.  Plot  o f D vs ( h  z  -  + k  2  + l ) 2  5  2  from  Table  p a t t e r n #23406, 316 s . c . c . i n M g C l + 1% b r o m i n e - m e t h a n o l s o l u t i o n . 2  A16.  Diffraction  HCl, oxide  stripped  with  - I l l-  Table  A17.  316 S.C.C. i n M g C l Methanol Solution pattern  line  + H C l , Oxide  2  #23407  Din.  camera  dA°  Stripped  constant  0.39 0.64  I  4.90 2.98 2.51 2.10 1.72 1.61  0.76 0.91 1.11 1.18  6 7 8  1.28 1.35 1.43  9 10  1.49 1.42 1.34 1.27  11  1.50 1.58  12  1.62 .  Data p l o t t e d  1.21 1.18  FeC^O^  0  Q  2  + k  M VW  440 531  3.32 4.0 4.90 5.2 5.66 5.92  VW W W VW  621  6.32  533  6.56 6.93 7.14  = 1.91 A °  a  Jh  S M W M  i n F i g . A17, D vs ( h  parameter  ins-A°  111 220 311 400 422 511/333  0.228 Lattice  Bromine-  (hkl)  M M  S l o p e M = K = 0.228 i n .  a  1%  K = 1.91  V 1 2 3 4 5  with  = 8.38 A °  444 551/711  2  + k  2  +l  2  ) '  1.73 2.83  2  +l  2  Fig.  A17.  Plot  o f D vs  - 112  -  (h  + k  2  p a t t e r n #23407, 316 1% b r o m i n e - m e t h a n o l  2  + l ft 2  from Table  s.c.c. i n MgCl solution  2  A17.  Diffraction  + HCl, oxide  stripped  wi  - 113  Table  A18.  316 S.C.C. i n M g C l Methanol S o l u t i o n pattern  line  2  + H C l , Oxide  #23404  camera  Din.  dA°  Stripped with  constant  K = 1.91 i n s . A  I  FeCr 0L 2  V  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15  0.385 0.45 0.64 0.745 0.785 0.90 0.985 1.02 1.1 1.17 1.28 1.34 1.42 1.48 1.56  Data p l o t t e d Slope  4.96 4.24 2.98 2.56 2.43 2.12 1,94 1.88 1.74 1,63 1,49 1.43 1.34 1.29 1.22  a  a  0  S M WW WW W M M VW VW W W  i n F i g . A18, D vs ( h + k 2  = 1.91 A ° 0.226  Lattice  111 220 311 222 400 331 422 511/333 440 531 620 533 444  w  °  parameter  a  Q  = 8.45 A °  t  0  </h  2  + k  (hkl)  M WW M  M = K = 0.226 i n .  1% B r o m i n e -  2  + l )"' 2  1.73 —  2.83 3.32 3.46 4.0 4.36 4.90 5.2 5.66 5.92 6.32 6.56 6.93  2  + I  2  - 114  Fig.  A18.  -  P l o t o f D vs ( h + k + l ) ^ f r o m T a b l e A18. Diffraction pattern #23404, 316 s . c . c . i n M g C l + H C l , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . 2  2  2  2  - 115  Table  A19.  316 S.C.C. i n M g C l Methanol Solution p a t t e r n #23483  line  -Din.  5 6 7 8 9 10 11 12 13 14  1.1 1.15 1.25 1,25 1.34 1.39 1.45 1.52  ;  15  Data p l o t t e d Slope  + CoCl  2  , Oxide  camera  dA°  0.365 0.60 0.70 0.80 0.845 0.94 1.04  1 2 3 4  2  -  constant  I  M M S VW M WW W M  1.57 1,44 1,44 1.34 1.30 1.24  WW WW WW VW W VW  1.18  VW  i n F i g . A19, D vs ( h  Lattice  0  = 1.80 A ° 0.212 parameter a  Q  = 8.49 A °  with  K = 1.80  FeCr^Q, (hkl)  V  4.93 3.0 ' 2,57 2.25 2.13 1.92 1.73 1.64  M = K = 0.212 i n .  a  Stripped  111 220 311  400 331 422 511/333  2  + k  2  1%  Bromine-  ins*A°  /h  2  + k2  1.73 2.83 3.32  -  4.0 4.36 4.90 5.2  -  -  531 531 620 533 4.44  5.92 5.92 6.32 6.56 6.93  551/711  7.14  + 1*)'  + 12  •  j  - 116 -  (h * k • I )i 2  Fig.  A19.  Plot  o f D vs  (h  2  + k  2  2  + l  2  2  ) ^ from  p a t t e r n #23483, 316 s . c . c . i n M g C l w i t h 1% b r o m i n e - m e t h a n o l s o l u t i o n  Table 2  A19.  + CoCl , 2  Diffraction oxide  stripped  - 117  Table  A20.  316 S.C.C. i n M g C l Methanol S o l u t i o n . p a t t e r n -#23472  •  ' line  D in.  -  + CoCl  2  I V  4.93 3.0 2.54  4 5 6 7 8  0.86 1.04 1.09  2.09 1.73 1.65 1,50 1.29 1.22  Slope  1.20 1.40 1.47 1.64 1.71  1.10 1.05  Lattice  D  w w  = 1.80 A ° 0.213 parameter  a  D  = 8.45 A °  ins«A°  FeCr20it  Jh  400 422 511/333 440 533 444 553/731  W  (h  Bromine-  K = 1.80  111 220 311  W M W  i n F i g . A20, D vs  1%  2  + k  (hkl)  M M S M W  M = K = 0.213 i n .  a  Stripped with  constant  dA°  0.365 0.60 0.71  Data p l o t t e d  , Oxide  camera  1 2 3  9 10 11  2  800  2  + k  2  + I ) 2  1.73 2.83 3.32 4.0 4.9 5.2 5.66 6.56 6.93 7.68 8.0  2  + I  2  - 118  Fig.  A20.  -  P l o t o f D vs ( h + k + l )* f r o m T a b l e A20. Diffraction pattern #23472, 316 s . c . c . i n M g C l + C o C l . o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n 2  2  2  5  2  2  >  - 119  Table  A21.  316 S.C.C. i n M g C l  -  + CoCl  2  Methanol S o l u t i o n p a t t e r n #23474  • line  2  , Oxide  camera  dA°  Din.  Stripped  constant  K =1.82  I  FeCraOi^ (hkl)  V 1 2 . 3 4 5 6 7 8 9 10 11 12 13 14  0.365 0.60  4.99 3,03  0.70 0.74 0.85  2,6 2.46 2.14  0.92 1.04 1.10 1.20 1.255 1,34  1.98 1,75 1.65 1,52 1.45 1,36  1.40 1,47 1.51  M = K_ a  a  Lattice  D  M M S  111 . 220 311  W M  222 400 331  Bromine-  ins*A°  Jh  2  + k  2  1.73 2.83 3.32 3.46 4.0  1,30 1.24  440 531 620 533 444  4.36 4.90 5.20 5.66 5.92 6.32 6.56 6.93  1.21  VW  711/551  7.14  A21, D vs ( h  = 0.212 i n .  o  = 1.82 A ° 0.212 parameter  1%  VW W M M VW VW W W  Data p l o t t e d i n F i g . Slope  with  a  0  = 8.58  A  0  422 511/333  2  + k  2  +  l  2  )  h  +l  2  - 12Q  -  (h** k * I* )* 2  Fig.  A21.  Plot  o f D vs  pattern with  (h  2  + k  #23474, 316  2  + l  2  s.c.c.  1% b r o m i n e - m e t h a n o l  ) ^ from Table i n MgCl  solution.  2  A21.  + CoCl , 2  Diffraction oxide  stripped  - 121  Table  A22.  310 S.C.C. i n M g C l , , O x i d e Solution pattern  •  -  line  #22205  Di n .  Stripped  camera  dA°  constant  I  6 7 8 9 10 11 1  0.39 0.52 0,64  4.9 3.68 2.98  M VW W  0.72 0.75 0.86  2.66 2.55 2.22  0.91 1.04 1.13  2.10 1.84 1.69 1,62 1,48  VW S VW M VW VW W M  1.30  VW  1.18 1.29 1.27  12  Data p l o t t e d i n F i g . Slope  A22, D vs ( h  M = K » 0.227 i n .  a  D  = 1.91 A ° 0.227  Lattice  parameter a  D  = "8.41 A °  1%  Bromine-Methanol  K = 1.91  ins-A°  Jh  FeCrgO^  V 1 2 3 4 5  with  2  +  k  2  (hkl) 111  1.73 _  220  2.83 _  311  3.32 _  400  4.0  -  -  -  422 333/511 440 533  2  + k  2  + l  2  f  2  -  4.9 5.2 5.66 6.56  +l  2  - 122  Fig.  A22.  -  P l o t o f D vs ( h t k + l ) ' f r o m T a b l e A22. Diffraction p a t t e r n #22205, 310 s . c . c . i n M g C l , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . 2  2  2  5  2  - 123  Table  A2 3.  -  310 S.C.C. i n MgClg , O x i d e Methanol S o l u t i o n p a t t e r n #22200  1 2 3 4 5 6 7 8 9 10 11 12 13 ,  Slope  Lattice  (hkl)  0  222  2.11 1.92 1,70 1.61 1.48 1.41  Dots VW VW WW W VW VW  1.32 1,29 1.21  Dots Dots  o  = 1.88 A ° 0.225 a  D  = 8.36 A °  2.83 3.32 3.46  311 400 331 422 333/511 440 531 620 533 444  Dots  i n F i g . A23, D vs ( h  parameter  + k  220  0.89 0.98  Q  2  1.73  M = K = 0.225 i n .  a  k  111  2.38  a  Jh  C  0  Dots Dot a S S  0.79  Data p l o t t e d  2  ins»A  M  2.96 2.54  1.56  Bromine-  K = 1.88  V  4.82 4.48 3.48  1.42 1.47  14 15  1%  FeCr  I  0.39 0.42 0.54 0.635 0.74  1.11 1.17 1.27 1.335  with  camera c o n s t a n t  dA°  Din.  line  Stripped  2  + k  2  + l  4.0 4.36 4.9 5.2 5.66 5.92 6.32 6.56 6.93  2  f  2  2  + l  2  ,  _ 124  _  ( h * k * I )£ 2  Fig.  A23.  Plot  o f D vs  pattern  (h  2  + k  #22200, 310  bromine-methanol  2  2  2  + l  2  s.c.c.  solution.  )  2  from Table  i n MgCl , 2  A23.  oxide  Diffraction  stripped  with  1%  - 125  Table  A24.  -  310 S.C.C. i n MgCl, , O x i d e S t r i p p e d w i t h 1% B r o m i n e Methanol S o l u t i o n p a t t e r n #22196 c a m e r a c o n s t a n t K = 1.88 i n s « A °  line  Di n .  1 2 3 4  0.395 0.52 0.64 0.72  5 6 7  0.75 0.86 0.915 0.98 1,04  8 9 10 11 12 13  1.11 1.18 1.275 1.325  14 15  1.47 1.57  dA°  4.76 3,62 2.94 2,61 2.51 2,19  a  G  2,06 1.92 1,81 1.69 1.59 1,47 1.42 1.28  M VW VW  422 511/333 440 531 533  1.20  VW  444  = 1.88 A °  a  Q  = 8.36 A °  + k  1.73  -  -  220  2.83  -  3.32  -  -  400 331  4.0 4.36  -  w  A24, D v s ( h  2  (hkl)  311  o  parameter  Jh  l t  S WW S WW WW VW  0.225 Lattice  2  111  M = K = 0.225 i n . a  FeCr 0  V  M VW W WW  Data p l o t t e d i n F i g . Slope  I  2  + k  2  +  -  l) 2  h  4.90 5.2 5.66 5.92 6.56 6.93  2  +l  2  - 126  Fig.  A24.  Plot  o f D vs  pattern  (h  2  -  + k  #2219.6, 310  bromine-methanol  2  + l  2  s.c.c.  solution.  ) '  2  from Table  i n MgCl , 2  A24.  oxide  Diffraction  stripped  with  1%  :  - 127  Table  A25.  •  -  310 S.C.C. i n MgClg , O x i d e S t r i p p e d w i t h C e l l u l o s e Acetate p a t t e r n #23146 c a m e r a c o n s t a n t K = 2,28 i n s - A °  D in.  line  1 2 3 4 5  dA°  I  0.465 0.64  4.90 3.56 3,00 2.53  11 12 13  6.76 0.90 1.09 1.22 1.325 1,41 1.54 1.61 1.72 1.78 1.885  2.09 1,87 1,72 1,-62 1.48 1.42 1.33 1,28 1.21  14  1.95  1.17  6 7 8 9 10  Data p l o t t e d Slope  Lattice  Q  c  1.73  -  -  220 311  2.83 3.32 4.0  400 331 422 511/333  4.36 4.9 5.2  WW W VW  440 531 620 533 444  5.66 5.92 6.32 6.56 6.93  VW  551/711  7.14  = 2.28 A ° 0.272 a  111  M M W  i n F i g . A 25, D vs ( h  parameter  + k  Jh  2  4  (hkl)  M WW M S M Dots W  M = K = 0.272 i n .  a  FeCr20  V  = 8.38 A °  2  + k  2  + l  2  f'  2  + l  2  - 1 2 § --  - 129  Table  A26._  310 S.C.C. i n M g C l , p a t t e r n #23124 2  line  Din.  1 ' 2 3 4 5 6 7 8  0.475 0.545 0.63 0.78 0.905  dA°  I  4.86 4.24 3.67  M  1.72 1.62 1.48  1.56 1.62 1.74  11 12 ' 13  1.43 1,33  1.80  1.28  Data p l o t t e d i n F i g .  Slope  M = K  a  Oxide S t r i p p e d with C e l l u l o s e A c e t a t e c a m e r a c o n s t a n t K = 2.31 i n s - A °  2.96 2.55 2.10 1.83  1.1 1.26 1.34 1.43  9 10  -  = 2.31 A °  parameter  a  Q  •= 8.40  A  0  2  1.73  -  -  2.83 3.32 4.0  -  + k  2  2  -  -  422 511/333 440 531 620 533  2  + k  111  220 311 400  M M Dots Dots W  A26, D vs ( h  Jh  4  -  M Dots W  0.275 Lattice  2  Dots Dots M S  = 0.275 i n .  0  FeCr 0 (hkl)  V  +  l ) 2  h  4.9 5.2 5.66 5.92 6.32 6.56  +l  2  - 130-  Fig.  A26.  Plot  o f D vs  pattern  (h  2  + k  #23124, 310  cellulose  acetate  -  2  + l  2  s.c.c.  ) " from Table 1  i n MgCl , 2  A26.  oxide  Diffraction,  stripped  with  - 131  Table  A27.  -  310 S.C.C. i n M g C l , p a t t e r n #23403  Oxide  2  line  Di n .  dA°  Stripped with Cellulose c a m e r a c o n s t a n t K = 2.28  2  V 1 2 3 4  0.465 0.53 0.76 0.89 0.935  4.90 4,-30 3.00 2.56 2.44  9 10  1.08 1,17 1.33 1.41 1.54  2.11 1.-95 1,-71 1.62 1.48  11 12 13  1.59 1,72 1.78  1,43  14  1.84  5 6 7 8  1,-33 1.28 1.24  Data p l o t t e d  a  a  0  0.270 Lattice  parameter  a  D  = 8.44 A °  •220 311  2.83 3.32 3.46 4.0 4.36 '4.9  -  222  WW WW VW WW  = 2.28 A °  1.73  400 331 422 511/333 440 531 620 533  M •M  o  + k  111  -  Dots W  S l o p e M = K = 0.270 i n .  2  (hkl)  M Dots M S W M  i n F i g . A27, D vs ( h  Jh  YeCr 0k  I  Acetate ins«A°  444  2  + k  2  + l  2  )'  5.2 5.66 5.92 6.32 6.56 6.93  2  +l  2  - 132:  - 133 -  Table  A28.  310 S.C.C. i n M g C l Methanol S o l u t i o n p a t t e r n #23418  line  Stripped  with  camera  constant  K = 1.91 i n s ' A °  4.78 3.60 2.94 2.48 2.08 1.91 1,80 1.68 1,60 1,46 1,39 1.30 1,26 1.2 1.16  a  Lattice  0  = 1.91 A 0.231 parameter  a  Q  -  -  -  -  422 511/333 440 531 620 533 444 711/551  S W VW  w M W  = 8.27 A °  + k  2.83 3.32 4.0 4.36  220 311 400 331  S W Dots W M  0  2  1.73  111  S  i n F i g . A28, D vs ( h  /h  (hkl)  Dots M VS  S l o p e M = K = 0.231 i n .  1% B r o m i n e -  FeCr^O^  I V  0.40 0.53 0.65 0.77 0.92 1.00 . 1,06 1,14 1.2 1,31 1,37 1.46 1.51 1.6 1.65  Data p l o t t e d  + H C l , Oxide  dA°  Di n .  1 2 3 4 5 6 7 8 9 10 11 12 ' 13 14 15  2  2  + k  2  + l  2  X  s  4.9 5.2 5.66 5.92 6.32 6.56 6.93 7.14  2  +l  2  - 134  A28.  P l o t o f D vs ( h +. k + l ) " from T a b l e A28.' D i f f r a c t i o n p a t t e r n #23418, 310 s . c . c . i n M g C l + H C l , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . 2  2  2  2  2  - 135  Table  A29.  310 S.C.C. i n M g C l Methanol S o l u t i o n p a t t e r n #23417  line  D in.  -  + H C l , Oxide  2  camera  dA°  Stripped with constant  I  0.40 0.66 0.77  4 5 6 7 8  0.92 1.01 1.15 1.2 1.31  9 10 11 12  4.78 2.90 2.48 2.08 1.89 1.66 1.60 1,46  1.36 1.52 1.61  1.40 1.26 1.19  VW W W  400 331 422 511/333 440 531 533 444  1.66  1.15  W  711/551  i n F i g . A29, D vs ( h  S l o p e M = K = 0.232 i n . a  Lattice  0  o  = 1.91 A ° 0.232 parameter  a  D  = 8.23  A  0  Bromineins-A  t/h  2  0  + k  2  (hkl)  S M VS S VW VW M S  Data p l o t t e d  a  K = 1.91  FeCrgC^  V 1 2 3  1%  111 220 311  2  + k  2  + l  2  ' .1.73 2.83 3.32  )'  4.0 4.36 4.9 5.2 5.66 5.92 6.56 6.93 7.14  + 12  - 13.6 -  - 137  Table  A30.  310 S.C.C. i n M g C l  -  2  +CoCl ,Oxide  Stripped  with  camera  constant  K = 1.85  2  Methanol Solution p a t t e r n #23488  •  Din.  line  0.375 0.47  1 2 3  0.61 0.73  4 5  0.875 1.04  6 7 8 9 , 10 11  1.13 1.23 1.42 1.50 1.72  Data p l o t t e d Slope  1  dA°  4.93 3.94 3.03  M VW VW  2.53 2.11 1.78  s s  1.64 1.50 1,30 1,23 1.08  a  Lattice  Q  i n F i g . A30, D vs ( h  o  = 1.85 A ° 0.219  parameter a  Q  2  = 8.45 A °  1 +  /h  2  + k  1.73  -  -  220 311  2.83 3.32 4.0  -  -  511/333 440 533 444 553/731  + k  ins«A°  H I  400  2  Bromine-  (hkl)  Dots VW M WW W W  M = K = 0.219 i n . a  FeCr 0  1%  2  + l  2  )'  5.2 5.66 6.56 6.93 7.68  2  + I  2  - 138  Fig.  A30.  Plot  o f D vs  (h  _  2  + k  2  + l  2  )  2  from  Table  p a t t e r n #23488, 310 s . c . c . i n MgCl2 w i t h 1% b r o m i n e - m e t h a n o l s o l u t i o n .  A30.  + C0CI2,  Diffraction oxide  stripped  -  139  -  APPENDIX Appendix B c o n t a i n s examples surface hot  oxides  chloride  of. t h e  methanol  solution  at  voltage of  a gun  Kct p e a k .  and 20  of x-ray  different alloys  environments.  The  examined kv.  B  oxides i n the  spectrum  stress were  A l l spectrum  corroded  stripped  scanning  taken  i n the  with  electron  normalised  from  a 1%  fracture various bromine-  microscope  to the  chromium  -  00.  o  140 -  o  1  o  1.00,to Iz ZD  I  ft  0.75  o  u Q  0.50  N -I <  0.25L o  0.00 5.0  5.5  ENERGY  Fig-  Bl.  j. 6.0  6.5  7.0  7.5  8.0  KeV  S.E.M. x - r a y s p e c t r u m f r o m f r a c t u r e s u r f a c e o x i d e o f t y p e 304 s t r e s s c o r r o d e d i n M g C l 2 s o l u t i o n . Stripped with bromine-methanol s o l u t i o n .  -  Fig.  B2.  S.E.M. x - r a y 304  stress  141  spectrum  corroded  bromine-methanol  -  from  fracture  i n MgCl  solution.  2  + HCl  surface  o,*ide o f  type  solution  stripped  with  - 142 -  Fig.  B3.  S.E.M. x - r a y s p e c t r u m f r o m f r a c t u r e s u r f a c e o x i d e . o f t y p e s t r e s s c o r r o d e d i n MgCl2 + C0CI2 s o l u t i o n . Stripped with bromine-methanol s o l u t i o n .  304  -  F i g - B4.  143  -  S.E.M. x - r a y spectrum from f r a c t u r e s u r f a c e o x i d e o f t y p e 316 s t r e s s c o r r o d e d i n M g C l s o l u t i o n . S t r i p p e d w i t h brominemethanol s o l u t i o n . 2  -  5.0  Fig.  B5.  5.5  -  6.0  ENERGY  KeV  S.E.M. x - r a y  spectrum  stress  144  corroded  bromine-methanol  6.5  from  i n MgCl  2  fracture  7.0  surface oxide  + HCl s o l u t i o n .  solution.  7.5  8.0  o f type  Stripped with  316  -  ENERGY  Fig-  B6.  S.E.M. x - r a y  145  -  KeV  spectrum  from  stress corroded i n MgCl methanol s o l u t i o n .  2  fracture  + CoCl  2  surface oxide  solution.  of type  Stripped with  316 bromine-  -  *  5,0  5.5  ENERGY  Fig.  B7.  146  -  *  6.0  6.5  *  *  7.0  7.5  8.0  K eV  S.E.M. x - r a y s p e c t r u m f r o m f r a c t u r e s u r f a c e o x i d e o f t y p e 310 s t r e s s c o r r o d e d i n M g C l solution. Stripped with bromine-methanol s o l u t i o n . 2  - 147 -  o  5.0  5.5  ENERGY  Fig-  B8.  S.E.M. x - r a y  03.  o  03.  6.0  6.5  7.0  a  7.5  8.0  KeV  spectrum  from  stress corroded i n MgCl methanol s o l u t i o n .  2  fracture  +.HC1  surface oxide  solution.  o f type  Stripped with  310  bromine-  -  1 4  8  -  si  ENERGY  Fig.  B9.  S.E.M. stress  x-ray  KeV  spectrum  corroded  bromine-methanol  in  .from f r a c t u r e  MgCl2 + C0CI2  solution.  surface oxide  solution.  of type  Stripped with  310  

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