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Embrittlement of zinc crystals by mercury Kim, Jyung-Hoon 1966

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EMBRITTLEMENT OF ZINC CRYSTALS BY MERCURY  by" JYUNG-HOON KIM A THESIS SUBMITTED I N PARTIAL FULFILMENT , OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE IN THE DEPARTMENT OF METALLURGY  We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e s t a n d a r d r e q u i r e d from c a n d i d a t e s f o r . t h e degree o f MASTER OF APPLIED SCIENCE  THE UNIVERSITY OF BRITISH COLUMBIA January, 1  1966.  In presenting the  this thesis i n partial  r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t the U n i v e r s i t y  B r i t i s h C o l u m b i a , I a g r e e that, the available  f o r r e f e r e n c e and  mission for extensive p u r p o s e s may  be  Library  study.  the  I f u r t h e r agree that  Head o f my  w i t h o u t my  written  D e p a r t m e n t of  permission*  Metallurgy  The U n i v e r s i t y of B r i t i s h V a n c o u v e r 8, Canada F e b r u a r y 15th,  1966  Columbia,  of  per-  scholarly  Department or  I t i s understood that.copying  c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain  of  s h a l l make i t f r e e l y  c o p y i n g of t h i s t h e s i s f o r  g r a n t e d by  his representatives.  Date  fulfilment  or  s h a l l - n o t be  by publi-  allowed  THE  UNIVERSITY  O F BRITISH  V A N C O U V E R  8,  COLUMBIA  CANADA  F e b r u a r y 11th, 1966.  DEPARTMENT OF METALLURGY  •C O M M E N T S ON  THESIS  " E m b r i t t l e m e n t of Z i n c C r y s t a l s b y M e r c u r y " by Jyung-Hoon K i m  A t t h e o r a l p r e s e n t a t i o n h e l d i n t h e D e p a r t m e n t of M e t a l l u r g y o n W e d n e s d a y , J a n u a r y 26, 1966, i t w a s d e c i d e d that the t h e s i s s h o u l d be a c c e p t e d , but w i t h the f o l l o w i n g c o m m e n t s : 1.  2.  T h e q u a l i t y of t h e E n g l i s h c o m p o s i t i o n i s w e l l b e l o w t h e u s u a l s t a n d a r d n o r m a l l y e x p e c t e d of s t u d e n t s w h o s e n a t i v e language i s . E n g l i s h . However, by m a j o r i t y opinion, i twas a g r e e d that i n a c a s e w h e r e E n g l i s h i s not a student's m o t h e r language, i t i s p r e f e r a b l e that the t h e s i s be w r i t t e n i n i m p e r f e c t E n g l i s h a n d r e p r e s e n t the student's o w n w r i t i n g and t h i n k i n g , than to have p e r f e c t E n g l i s h a r i s i n g f r o m extensive r e w r i t i n g o r r e v i s i o n b y the s u p e r v i s o r . T h e o v e r r i d i n g c o n s i d e r a t i o n , h o w e v e r , m u s t be that the t h e s i s s h a l l b e s u f f i c i e n t l y w e l l w r i t t e n t o a v o i d a n y a m b i g u i t y of t h o u g h t o r m i s s t a t e m e n t s of f a c t . It w a s f e l t t h a t s o m e of t h e d e t a i l e d c o n c l u s i o n s e x p r e s s e d i n t h i s t h e s i s w e r e u n w a r r a n t e d b y t h e n a t u r e of t h e r e s u l t s . . H o w e v e r , i t w a s felt that t h i s c o u l d be due, i n p a r t , t o t h e l a n g u a g e p r o b l e m , a n d t h a t i n a n y c a s e , t h e q u a l i t y of t h e work generally warranted its acceptance.  i  ABSTRACT  A s t u d y has been u n d e r t a k e n  t o i n v e s t i g a t e the loss of d u c t i l i t y  and m o d i f i e d work h a r d e n i n g c h a r a c t e r i s t i c s o f z i n c s i n g l e c r y s t a l s  coated  w i t h mercury.  Important  r e s u l t s o f t e n s i l e t e s t s p e r f o r m e d under f i x e d  e x p e r i m e n t a l c o n d i t i o n s a r e summarized t o b e : (1)  i n c r e a s e i n c r i t i c a l r e s o l v e d shear s t r e s s , and i n c r e a s e o f work h a r d e n i n g s l o p e i n stage A and stage B  (2)  decrease  i n t r a n s i t i o n ' s t r a i n from stage A t o stage B  (3)  decrease  i n f r a c t u r e s t r e s s and f r a c t u r e  The understanding  strain.  r e s u l t s have been i n t e r p r e t e d i n t h e c o n t e x t o f t h e p r e s e n t o f d e f o r m a t i o n t h e o r y o f C.P.Hex. m e t a l s .  I n a d d i t i o n , r e l e v a n t mechanisms f o r c r a c k i n i t i a t i o n have been s t u d i e d w i t h t h e a i d - o f m i c r o s c o p i c o b s e r v a t i o n s o f deformed c r y s t a l s .  ii  ACKNOWLEDGEMENT  The  a u t h o r g r a t e f u l l y acknowledges t h e guidance o f Dr. E.  Teghtsoonian, the d i r e c t o r of t h i s  research.  He w i s h e s t o thank t h e members o f t h e f a c u l t y and f e l l o w graduate students  o f t h e Department o f M e t a l l u r g y f o r t h e i r c o n t i n u e d  support and  i n t e r e s t i n t h i s work.  S p e c i a l t h a n k s a r e extended t o Mr. R. R i c h t e r for. a s s i s t a n c e , w i t h equipment and Mr. R..G. B u t t e r s f o r t e c h n i c a l a d v i c e . The  author  i s g r a t e f u l f o r f i n a n c i a l , a s s i s t a n c e • p r o v i d e d by t h e  R e s e a r c h C o r p o r a t i o n , New Y o r k , t h e N a t i o n a l R e s e a r c h C o u n c i l o f Canada,,and C a n a d i a n W e s t e r n P i p e M i l l s o f P o r t Moody,, B.C.  iii  TABLE OF CONTENTS Page I . INTRODUCTION AND REVIEW OF THE LITERATURE ON EMBRITTLEMENT BY LIQUID METALS  1  A. INTRODUCTION  1  B. REVIEW OF THE LITERATURE ON "EMBRITTLEMENT BY LIQUID METALS ( i ) The E f f e c t o f L i q u i d M e t a l on t h e P l a s t i c D e f o r m a t i o n o f Polycrystalline Material  2 2  ( i i ) The E f f e c t o f L i q u i d M e t a l on t h e P l a s t i c D e f o r m a t i o n o f S i n g l e Crystals • ( i i i ) Survey o f Embrittlement Couples  8 9  C . THE AIM OF PRESENT INVESTIGATION I I . EXPERIMENTAL PROCEDURE  11  A. - MATERIAL  11  B. SPECIMEN PREPARATION  11  ( i ) Growth o f S i n g l e C r y s t a l s ( i i ) Surface Coating of the-Single  4  11 C r y s t a l s w i t h Mercury  C . - TENSILE TESTING  -  12 13  I I I . - EXPERIMENTAL RESULTS  15  A. . WETTING EXPERIMENT  15  ( i ) Zn-Hg System ( i i ) ' W e t t i n g Experiment w i t h P o l y c r y s t a l l i n e Zinc ( i i i ) W e t t i n g Experiment w i t h S i n g l e C r y s t a l Specimen B.  TENSILE TEST OF UNCOATED CRYSTALS  C.  THE EFFECT OF TIME OF IMMERSION ON THE•WORK HARDENING CHARACTERISTICS  15 16 - . . 16  23  iv  Table o f C o n t e n t s ( c o n t ' d ) Page D. THE EFFECT OF EXPOSURE TIME I N AIR AFTER MERCURY COATING ON THE WORK HARDENING CHARACTERISTICS  29  E. THE EFFECT OF PRESTRAIN AND MERCURY COATING ON THE WORK HARDENING CHARACTERISTICS  29  F. THE EFFECT OF MERCURY COATING AND HIGH TEMPERATURE ON THE WORK . HARDENING CHARACTERISTICS . . . . . .  3^  G. • SUMMARY OF RESULTS H. REPRODUCIBILITY OF THE RESULTS IV. METALLOGRAPHIC V. A.  . . .  38  OBSERVATIONS  .  DISCUSSION  k6 46  (i)  k6  Wetting C h a r a c t e r i s t i c s  '.  The D i f f u s i o n o f Mercury i n Z i n c  (i) (ii)  D.  k6  THE EFFECT OF MERCURY COATING- ON THE-CRITICAL RESOLVED SHEAR STRESS OF ZINC SINGLE CRYSTALS  C.  39  WETTING CHARACTERISTICS AND DIFFUSION OF MERCURY I N ZINC  (ii) B.  37  D i s l o c a t i o n Egress E f f e c t  . . . . . .......  S u r f a c e Drag E f f e c t  ( i i i ) Surface Anchoring E f f e c t THE EFFECT OF MERCURY COATING ON THE WORK- HARDENING. OF ZINC SINGLE CRYSTAL  k& k$ k$ 51 52  PROPOSED MECHANISM FOR CRACK INITIATION  55  CONCLUSION  59  V I I . APPENDICES  60  VI.  A. •B.  THERMODYNAMICS OF THE SPREADING' OF LIQUIDS ON SOLID PHASE DISLOCATION PIPE DIFFUSION  60 62  V  Table o f Contents (cont'd) Page C.  65  RESULTS OF. TENSILE TEST  70  D. . ESTIMATION OF ERRORS REFERENCES  .-  72  vi  LIST OF FIGURES Page. F i g . 1.  Mounting A p p a r a t u s  ik  F i g . 2.  Dimensions o f Mounted C r y s t a l  Ik  F i g . 3.  Hg-Zn System  l  F i g . k. F i g . 5. F i g . 6. F i g . 7F i g . 8.  F i g . 9«  F i g . 10.  15  .Weight Gained p e r U n i t A r e a o f t h e S u r f a c e b y P o l y c r y s t a l l i n e Specimens  17  Weight Gained p e r U n i t A r e a o f t h e S u r f a c e b y ' S i n g l e C r y s t a l Specimens  18  The Three Stage Shear S t r e s s - S t r a i n Curve f o r h.c.p. • S i n g l e ' Crystal  20  Shear S t r e s s - S t r a i n Curves f o r ' U n c o a t e d C r y s t a l s T e s t e d i n T e n s i o n a t Room• Temperature  22  Shear S t r e s s - S t r a i n Curves f o r C o a t e d C r y s t a l s Te.sted i n T e n s i o n a t Room Temperature (time o f immersion i n a i r a f t e r c o a t i n g : 5 mins.)  26  Shear S t r e s s - S t r a i n Curves f o r C o a t e d . C r y s t a l s T e s t e d . i n T e n s i o n a t Room Temperature (time o f immersion i n a i r a f t e r c o a t i n g : 10 and 15 mins.)  27  The E f f e c t o f Exposure Time a f t e r C o a t i n g - o n F r a c t u r e S t r a i n  29  F i g . 11. • S h e a r - S t r e s s - S t r a i n Curves f o r P r e s t r a i n e d and C o a t e d C r y s t a l s T e s t e d i n . T e n s i o n a t Room Temperature (amount o f p r e s t r a i n : 30$ ) F i g . 12.  Shear S t r e s s - S t r a i n C u r v e s f o r P r e s t r a i n e d - a n d C o a t e d C r y s t a l s T e s t e d - i n T e n s i o n a t Room Temperature . (amount o f p r e s t r a i n : . 100 and 105$)  31  .32  F i g . 13. -Shear S t r e s s - S t r a i n Curves f o r P r e s t r a i n e d and C o a t e d C r y s t a l s T e s t e d a t Room Temperature ' (amount o f p r e s t r a i n : 162 and 165$)  35  F i g . Ik.  The E f f e c t o f P r e s t r a i n and M e r c u r y C o a t i n g on "tf'^- Tf'gp  3^  F i g . 15.  The E f f e c t o f M e r c u r y - C o a t i n g and H i g h e r Temperatures on F r a c t u r e Strain  .......  F i g . 16. M i c r o p h o t o g r a p h o f Z X I - I - 3 F i g . 17. M i c r o p h o t o g r a p h o f ZXI-N-3  • • •  36 • • • • . . .-  -.  kO h0  • v i i  L i s t o f F i g u r e s (cont'd) Page F i g . 18.  M i c r o p h o t o g r a p h o f ZXI-N-2  .  .  . . . . . . . . . . .  F i g . 19. -Microphotograph o f ZXI-0-1+  kl 1+1  F i g . 20. - M i c r o p h o t o g r a p h o f ZXI-M-2  1+2  F i g . 21.  M i c r o p h o t o g r a p h o f ZXI-0-3  k2  F i g . 22.  M i c r o p h o t o g r a p h o f ZXI-V-2  F i g . 23.  M i c r o p h o t o g r a p h o f ZXI-V-1  F i g . 2k.  C r a c k I n i t i a t e d by C o a l e s c e n c e o f D i s l o c a t i o n s on M a t r i x B a s a l  1+3  . . . . . .  1+3  1+1+  P l a n e Propagates a l o n g B a s a l P l a n e i n Twin F i g . 25.  Crack I n i t i a t e d a t Kink W a l l  1+5  F i g . 26.  Crack I n i t i a t e d a t T e n s i l e Kink  ,1+5  F i g . 27.  Cracks I n i t i a t e d a t Tensile Kinks  F i g . 28.  Mercury M i g r a t i o n t o Newly-Exposed B a s a l P l a n e D u r i n g - D e f o r m a t i o n  1+7  F i g . 29.  F i s h e r S i n g l e - E n d e d Source  50  F i g . 30.  Schematic P i c t u r e o f F a n n i n g P r o c e s s a t B o t h Ends o f t h e Same  -  . .  S l i p Plane F i g . 31-  Geometry o f Twin i n Z i n c  F i g . 32.  Zener's Model f o r t h e N u c l e a t i o n o f C r a c k by D i s l o c a t i o n C o a l e s c e n c e as an A l t e r n a t i v e t o S l i p P r o p a g a t i o n Schematic P i c t u r e o f B u l l o u g h - Gilman - R o z h a n s k i i Model f o r C r a c k ' I n i t i a t i o n i n Zinc  P i g . 33.  1+5  53 .  55  56 58  viii  LIST: OF TABLES ^ Page 9  Table I .  E m b r i t t l e m e n t Couple  Table I I .  The V a l u e s o f Parameters O b t a i n e d b y - T e n s i l e T e s t i n g Uncoated 21  -. C r y s t a l s Table I I I .  Table IV.  The E f f e c t o f Immersion-Time on t h e Work H a r d e n i n g Characteristics - .. ..  2k  The E f f e c t o f Exposure Time i n A i r a f t e r Mercury. C o a t i n g on 28  Work Hardening. C h a r a c t e r i s t i c s T a b l e V.  The E f f e c t o f P r e s t r a i n and M e r c u r y C o a t i n g on Work H a r d e n i n g Characteristics  Table V I .  . .  31  ...........  35  .-  The E f f e c t o f Mercury C o a t i n g and P r e h e a t i n g on Room Temperature D e f o r m a t i o n C h a r a c t e r i s t i c s  \  -1 -  I  A.  INTRODUCTION AND REVIEW OF THE LITERATURE ON EMBRITTLEMENT BY LIQUID METALS  INTRODUCTION The e f f e c t s o f s u r f a c e environment on t h e p l a s t i c d e f o r m a t i o n  o f m a t e r i a l s have been observed f o r many y e a r s .  According t o various  i n v e s t i g a t i o n s , t h e m a t e r i a l s i n f l u e n c e d range from stone and g l a s s t o pure m e t a l s and a l l o y s i n environments w h i c h a r e e i t h e r gases o r l i q u i d s .  Many i n v e s t i g a t o r s have a t t a c k e d t h i s f i e l d under a v a r i e t y o f headings such as s t r e s s c o r r o s i o n , hydrogen e m b r i t t l e m e n t , c o r r o s i o n f a t i g u e , l i q u i d m e t a l c o r r o s i o n and f a t i g u e . There a r e many s i m i l a r i t i e s e v i d e n t i n a l l o f t h e t o p i c s mentioned.  just  However, i n t h i s p a p e r , p a r t i c u l a r a t t e n t i o n w i l l be f o c u s s e d  on those i n v e s t i g a t i o n s r e l a t i n g t o l i q u i d m e t a l e m b r i t t l e m e n t .  The e f f e c t o f s u r f a c e a c t i v e media on t h e m e c h a n i c a l b e h a v i o r o f m a t e r i a l s has been s t u d i e d e x t e n s i v e l y i n t h e S o v i e t U n i o n s i n c e t h e e a r l y work o f Rehbinder i n 1931.  L i q u i d m e t a l e m b r i t t l e m e n t was c o n s i d e r e d w i t h i n  the b r o a d f i e l d o f p h y s i c o c h e m i c a l mechanics whereby t h e s u r r o u n d i n g media m o d i f y t h e p h y s i c a l and m e c h a n i c a l p r o p e r t i e s o f m a t e r i a l s a s a r e s u l t o f t h e f o r m a t i o n o f adsorbed s u r f a c e l a y e r s . s o l i d , l i q u i d o r gaseous.  P o s s i b l e s u r f a c e a c t i v e media can be  The main e f f e c t o f such a l a y e r i s t o reduce t h e  s t r e n g t h and hardness o f t h e m a t e r i a l w i t h i n c r e a s e d d u c t i l i t y . I n c o n s i d e r i n g l i q u i d m e t a l e m b r i t t l e m e n t , we u s u a l l y observe d r a s t i c decrease i n d u c t i l i t y .  A l s o t h e r o l e o f d i s l o c a t i o n c a n n o t be o v e r -  - 2 -  l o o k e d because some p l a s t i c d e f o r m a t i o n always p r e c e d e s e m b r i t t l e m e n t by l i q u i d metals.  Any d i s l o c a t i o n mechanism f o r c r a c k i n i t i a t i o n presupposes some  s t a b l e o b s t a c l e s t o t h e motion o f d i s l o c a t i o n s .  With p o l y c r y s t a l l i n e materials,  t h i s f u n c t i o n i s u s u a l l y performed b y a g r a i n boundary. o b s e r v e d t h a t , i n some m a t e r i a l , c r a c k s may be i n i t i a t e d 1  grains .  However i t has been i n the center of 2  S t u d i e s on s i n g l e c r y s t a l s , p a r t i c u l a r l y cadmium , have p r o v i d e d  good e v i d e n c e t h a t b o t h c r a c k i n i t i a t i o n and p r o p a g a t i o n c a n be a s s i s t e d b y the  presence o f a c t i v e l i q u i d m e t a l atoms.  Therefore i t i s quite conceivable  t h a t l i q u i d m e t a l environments e i t h e r p r o v i d e a b a r r i e r o r s t a b i l i z e some p o t e n t i a l b a r r i e r t o d i s l o c a t i o n movement. B.  REVIEW OF THE LITERATURE ON EMBRITTLEMENT BY LIQUID METALS (i)  The E f f e c t o f L i q u i d M e t a l on t h e P l a s t i c D e f o r m a t i o n o f P o l y c r y s t a l l i n e Materials The l o s s o f s t r e n g t h and d u c t i l i t y o f m e t a l s under s t r e s s and i n  c o n t a c t w i t h s u r f a c e a c t i v e m e t a l s has been t h e s u b j e c t o f many i n v e s t i g a t i o n s . Reported r e s u l t s i n d i c a t e disagreement on t h e n a t u r e o f t h e e m b r i t t l e m e n t and p r i n c i p a l mechanisms i n v o l v e d r e f l e c t i n g t h e c o m p l e x i t y o f t h e problems  related  w i t h l i q u i d metal embrittlement.  To d e v e l o p t h e p i c t u r e t h a t b o t h s t r e s s and l i q u i d m e t a l s a r e n e c e s s a r y c o n j o i n t l y f o r t h e i n i t i a t i o n o f e m b r i t t l e m e n t , H e y n , Rawdon , and 3  Moor and B e c k i n s a l e  5  have done e x p e r i m e n t s w i t h b r a s s w e t t e d by mercury.  4  It  was t h e i r b e l i e f t h a t t h e s i m u l t a n e o u s e f f e c t s o f i n t e r n a l s t r e s s e s i n t h e m a t e r i a l and t h e p e n e t r a t i o n o f mercury d e p o s i t e d a t t h e g r a i n b o u n d a r i e s o f  - 3 -  the b r a s s caused i n t e r g r a n u l a r c r a c k i n g .  I n v e s t i g a t i o n o f e l e v a t e d temperature  e f f e c t s p e r m i t t e d t h e use  o f a wide range o f l i q u i d m e t a l s i n a d d i t i o n t o mercury.  Miller  6  determined  the t e n s i l e p r o p e r t i e s o f 6o/kO and jo/30 b r a s s e s c o a t e d w i t h l i q u i d t i n , up t o 350°C, and f o u n d t h e e m b r i t t l e m e n t  l e a d , and s o l d e r a t temperature  p r o c e s s was s i m i l a r t o t h a t o f b r a s s b y mercury a l t h o u g h h i g h s t r e s s e s were required f o r fracture.  R e c e n t l y , Rosenberg and C a d o f f  7  p o i n t e d out t h a t t h e wide v a r i a t i o n  i n r e s u l t s were due t o t h e wide v a r i e t y o f e x p e r i m e n t a l programs c a r r i e d o u t , and f o c u s s e d i n t e n s i v e a t t e n t i o n t o a d e t a i l e d s t u d y o f one system, a l l o y s , w e t t e d w i t h mercury and mercury base s o l u t i o n s .  copper  They came t o f o l l o w i n g  conclusions:  (1)  The e l o n g a t i o n o f copper i n mercury i s g r e a t e r t h a n t h a t o f t h e Cu-Zn a l l o y , t h e l a t t e r b e i n g g e n e r a l l y c o n s i d e r e d a case o f e m b r i t t l e m e n t .  (2)  The e f f e c t o f g r a i n s i z e on y i e l d s t r e n g t h , f r a c t u r e s t r e n g t h , and l o s s o f e l o n g a t i o n a r e t o be n o t e d . versus g r a i n s i z e , D / -1  T  f  = T  The r e l a t i o n s h i p between f r a c t u r e  stress  c a n be r e l a t e d b y  2  + K_D /2 -1  0  f  l  where T o f and K_ a r e c o n s t a n t s o f t h e system. (3)  The f r a c t u r e c h a r a c t e r i s t i c s o f copper-aluminum, c o p p e r - g o l d , and coppergermanium a l l o y s wet w i t h mercury a r e s i m i l a r t o t h o s e d e s c r i b e d f o r t h e c o p p e r - z i n c system.  The s u s c e p t i b i l i t y t o e m b r i t t l e m e n t f o r a l l f o u r  systems i s i n t h e o r d e r z i n c ^ a l u m i n u m <germanium ^ g o l d .  - k -  (k)  I n c o p p e r - z i n c system, t h e r e l a t i o n between the y i e l d s t r e s s the g r a i n s i z e D /z 1  -tys where Toy (5)  The  and K  2  i s given  = Toy  +K  "fy  s  and  by  2  D* ^ 1  2  a r e c o n s t a n t s o f system.  w e t t i n g a c t i o n a s s o c i a t e d w i t h changing the l i q u i d - m e t a l c o m p o s i t i o n  i s reintroduced  as a s i g n i f i c a n t v a r i a b l e .  The  c o n c e p t s of  surface  energy a l o n e do not appear t o e x p l a i n t h e wide v a r i a t i o n (an i n c r e a s e  in  f r a c t u r e s t r e s s over t h a t o b t a i n e d  i n pure mercury) caused by changes i n  the l i q u i d - m e t a l c o m p o s i t i o n .  i n t e r a c t i o n of l i q u i d metal w i t h  The  the  s o l i d a t t h e r o o t of the s t a b i l i z e d o r a d v a n c i n g c r a c k i s n e c e s s a r y f o r a complete u n d e r s t a n d i n g o f the problem. (6)  The  g r a i n s i z e dependence o b s e r v e d i n t h e p r e s t r a i n e x p e r i m e n t s i n d i c a t e s  t h a t , f o r l a r g e g r a i n samples, t h e d i s l o c a t i o n p i l e - u p dependence on g r a i n d i a m e t e r c o n t r o l s t h e f r a c t u r e and t h u s t h e r e  i s greater  suscepti-  b i l i t y at l a r g e r g r a i n s i z e s . (7)  The  measurements f o r f r a c t u r e b o u n d a r i e s appear t o be somewhat s c a t t e r e d  a t f i r s t g l a n c e , but  c l o s e r i n s p e c t i o n shows t h a t t h e a n g l e between s l i p  p l a n e s i n a d j a c e n t g r a i n s i s not o f major s i g n i f i c a n c e , t h a t coincidence  only  o f s l i p d i r e c t i o n i s n e c e s s a r y f o r the i n h i b i t i o n o f mercury  penetration. (ii)  The  E f f e c t o f L i q u i d M e t a l on the P l a s t i c D e f o r m a t i o n o f S i n g l e C r y s t a l s  Likhtman and Shchukin  3  i n v e s t i g a t e d the e f f e c t o f a mercury c o a t i n g  on the d e f o r m a t i o n c h a r a c t e r i s t i c s o f z i n c s i n g l e c r y s t a l s . orientation  X  c  = k8°  were t e s t e d a t room t e m p e r a t u r e . ( X  Q  The  c r y s t a l s of  = a n g l e between  - 5 -  t e n s i l e a x i s and s l i p p l a n e ) .  They found t h a t the s h e a r s t r e s s and  s t r a i n a t f r a c t u r e were r e s p e c t i v e l y reduced f r o m l^OKg/cm and 2  t o 20Kg/cm  shear  260$  inair  and 10$ i n mercury.  2  Shchukin e t a l  9  s t u d i e d t h e o r i e n t a t i o n dependence o f normal  s t r e s s a t f r a c t u r e T^r' and s h e a r s t r a i n a t f r a c t u r e "ftp f o r amalgamated zinc single crystals.  They e s t a b l i s h e d a c r i t e r i o n f o r t h e b r i t t l e f r a c t u r e  w h i c h a p p r o x i m a t e s t h e c o n s t a n c y o f t h e p r o d u c t o f normal . and c l e a v a g e s t r e s s r e l a t i v e t o the b a s a l plane of d i f f e r e n t l y o r i e n t e d z i n c monocrystals. T h i s c o n s t a n c y i s e x p r e s s e d by  ^F  C if where K = k (  *  F  *  K  "  5  l/2  I  /L)  , k being a dimensionless constant of order u n i t y ,  G the shear modulus,  2f t h e s p e c i f i c f r e e energy and L t h e l e n g t h o f s l i p  plane. The e f f e c t o f t e m p e r a t u r e and a l l o y l i q u i d m e t a l s w i t h v a r i o u s c o n c e n t r a t i o n were i n v e s t i g a t e d by R e h b i n d e r , Kochanova, Bryukhanova and Labzin  1 0  "  1 2  .  Z i n c s i n g l e c r y s t a l s i n t h e form o f 0.5mm w i r e were c o a t e d  w i t h t i n , l e a d , a l l o y s o f t i n and l e a d i n v a r i o u s c o n c e n t r a t i o n , and  mercury.  W i t h t i n - c o a t e d z i n c c r y s t a l s t e s t e d i n t e n s i o n a t a temperature  below t h e  m e l t i n g p o i n t o f t h e Zn/Sn e u t e c t i c , a s l i g h t i n c r e a s e i n t e n s i l e  strength  was  observed.  ductility  A t h i g h e r t e m p e r a t u r e (350° and 4-00°C) t h e s t r e n g t h and i  decreased remarkably.  A l s o a t t h e same t e m p e r a t u r e t h e n a t u r e o f  f r a c t u r e changed from a d u c t i l e t y p e (uncoated) t o a b r i t t l e t y p e with liquid t i n ) .  (coated  Both t h e f r a c t u r e s t r e s s and e l o n g a t i o n were reduced.  This  - 6 -  was (1)  c o n s i d e r e d t o be r e l a t e d An  increase  s o l u b i l i t y o f z i n c i n l i q u i d t i n as the  r a i s e d f r o m 350  was (2)  i n the  with:  to^O'C; 1  A c o r r e s p o n d i n g d e c r e a s e i n the i n t e r f a c e s u r f a c e However, Kamdar and W e s t w o o d  R u s s i a n work d i d not  a t t e n t i o n t o the o b j e c t to s l i p .  13  tension.  p o i n t e d out the f a c t t h a t  the  i n c l u d e an i n t e r p r e t a t i o n i n v o l v i n g the e x i s t e n c e  nature of stable obstacles  obstacles  temperature  t o the m o t i o n of d i s l o c a t i o n s .  of r e v e a l i n g the n a t u r e o f any  They p a i d  suitably  or  special  stable  F o r t h i s p u r p o s e , t h e b e h a v i o r o f amalgamated s i n g l e  asymmetric b i c r y s t a l s were c a r e f u l l y s t u d i e d . c r y s t a l s i n t o t h r e e groups based on Xo,  They c l a s s i f i e d t h e  and  single  t h e a n g l e between specimen a x i s  and  the (0001) b a s a l p l a n e . I n group I where t w i n n i n g and  XQ^'—15°* c r y s t a l s were deformed p r i n c i p a l l y by  b o t h p a r t i a l l y amalgamated and  chemically  polished  specimens  f a i l e d a f t e r o n l y a few p e r c e n t s t r a i n by secondary c l e a v a g e on the planes of a t w i n .  I t was  s u s p e c t e d t h a t , under c e r t a i n c i r c u m s t a n c e s , t w i n  b o u n d a r i e s would s e r v e as s t a b l e b a r r i e r s t o d i s l o c a t i o n m o t i o n .  To examine  t h i s hypothesis, they introduced twins i n t o c r y s t a l s of o r i e n t a t i o n X and  by g e n t l y  (0001)  indenting  t h e c r y s t a l s w i t h t h e b l u n t end  Q  =  of a needle.  Then o x i d e f r e e specimens were amalgamated i n t h e v i c i n i t y of t w i n s and strained.  C l e a v a g e c r a c k s were observed t o i n i t i a t e a t t w i n boundary and  p r o p a g a t e a l o n g b a s a l p l a n e s o f the m a t r i x c r y s t a l .  25°  lightly to  -7 -  I n group I I where 15° ( X  0  ( 70°, p a r t i a l l y amalgamated c r y s t a l s  deformed i n a d u c t i l e manner and d i d n o t f r a c t u r e u n t i l s h e a r s t r e s s e s o f the o r d e r 600-1000g/mm and s t r a i n s o f o r d e r 12,-250$ were a t t a i n e d . 2  F r a c t u r e o f b o t h p a r t i a l l y c o a t e d and u n c o a t e d c r y s t a l s e v e n t u a l l y o c c u r r e d a f t e r r e p e a t e d t w i n n i n g and u s u a l l y by secondary c l e a v a g e on t h e (0001) plane o f a t w i n .  O c c a s i o n a l l y , amalgamated specimens d i d f r a c t u r e a t  r e l a t i v e l y low s t r a i n s (20-60$) and e x a m i n a t i o n o f t h e s e specimens  revealed  t h a t , i n a l l i n s t a n c e s , f r a c t u r e had i n i t i a t e d a t k i n k bands w h i c h formed i n the v i c i n i t y o f the g r i p s d u r i n g the t e n s i l e t e s t .  I n group I I I where X ^ 0  70° > c r y s t a l s were s i g n i f i c a n t l y  e m b r i t t l e d b y mercury and f r a c t u r e o c c u r r e d always a t a k i n k band formed i n t h e amalgamated gauge s e c t i o n . They c a r r i e d out f u r t h e r experiments w i t h p a r t i a l l y amalgamated asymmetric b i c r y s t a l s and found t h a t c l e a v a g e c r a c k s were i n i t i a t e d a t t h e g r a i n boundary o f b i c r y s t a l s , and p r o p a g a t e d c o m p l e t e l y t h r o u g h t h e c r y s t a l s . T h e i r c o n c l u s i o n s can be summarized (1)  as f o l l o w s :  A d s o r p t i o n o f t h e l i q u i d m e t a l a t some s t a b l e o b s t a c l e t o s l i p i s a necessary c o n d i t i o n o f l i q u i d metal embrittlement. Consequently, z i n c s i n g l e c r y s t a l s o r i e n t e d f o r s i n g l e s l i p and t e s t e d i n t e n s i o n a r e n o t e m b r i t t l e d u n l e s s t h e l i q u i d m e t a l s a r e adsorbed s p e c i f i c a l l y a t k i n k bands formed n e a r the g r i p s d u r i n g d e f o r m a t i o n .  (2)  Experiments w i t h amalgamated b i c r y s t a l s p r o v i d e c o n v i n c i n g s u p p o r t f o r cleavage f r a c t u r e i n z i n c p r o p o s e d b y Likhtman-Shchukin and d e r i v e d from an a n a l y s i s by G i l m a n .  - 8 -  The e f f e c t o f mercury on t h e c l e a v a g e f r a c t u r e energy o f z i n c c r y s t a l s was a l s o i n v e s t i g a t e d by Westwood and KamdariA.  single  They a p p l i e d  Obreimov-Oilman c l e a v a g e t e c h n i q u e i n w h i c h p a r t i a l c r a c k was  i n t r o d u c e d by  c r a c k i n i t i a t i n g j i g and p r e v e n t e d from p r o p a g a t i n g c o m p l e t e l y t h r o u g h the specimen by t h e a p p l i c a t i o n o f a s m a l l compressive the d i r e c t i o n o f p r o p a g a t i o n .  stress perpendicular to  They found t h e t o t a l energy i n v o l v e d i n t h e  p r o p a g a t i o n o f a c r a c k , 0 can be e x p r e s s e d by t h e r e l a t i o n  -v *  k  r  0  where 0^ i s t h e c o e f f i c i e n t o f e m b r i t t l e m e n t w h i c h r e l a t e s t h e  energy  r e q u i r e d t o s e p a r a t e atoms a t c r a c k t i p i n the p r e s e n c e and absence o f mercury, i s a d i m e n s i o n l e s s v a r i a b l e depending upon t h e degree o f p l a s t i c a t t h e c r a c k t i p and independent of t h e f r a c t u r e p l a n e . 87 ± 5 e r g / c m (iii)  2  o f 7^  I n t h e i r work  , and  "0 o_;n(298 K)  and ^ n - H g ( 2 9 8 ° K ) t o be Z  Survey o f E m b r i t t l e m e n t P e r t s o v and R e h b i n d e r  a i d o f b i n a r y phase diagram.  if o  /  0.61  o  *  relaxation  i s t h e t r u e s u r f a c e energy w a s  d e t e r m i n e d t o be  0.12.  Couples 1 5  have s t u d i e d e m b r i t t l e m e n t c o u p l e s w i t h t h e  They found s e m i e m p i r i c a l r u l e s i n d i c a t i n g whether  o r not a g i v e n m o l t e n m e t a l Mi i s s t r o n g l y s u r f a c e a c t i v e i n r e g a r d t o a n o t h e r metal M  2  of higher m e l t i n g p o i n t .  T h e i r r e s u l t s can be summarized as f o l l o w s ;  (see T a b l e I ) . (1)  There i s c o n s i d e r a b l e r e d u c t i o n i n s t r e n g t h and d u c t i l i t y i f m e t a l Mi has a narrow, b u t f i n i t e , r e g i o n o f s o l u b i l i t y i n t h e s o l i d s t a t e i n t h e metal  M. 2  -  (2)  On the c o n t r a r y , no e m b r i t t l e m e n t  9  -  e f f e c t i s n o r m a l l y observed i f t h i s  s o l u b i l i t y r e g i o n i s v e r y wide or absent a l t o g e t h e r .  TABLE I Embrittlement  C.  Couple  Reduction i n strength of m e t a l under the e f f e c t o f a molten metal coating  No r e d u c t i o n i n s t r e n g t h o f m e t a l under t h e e f f e c t o f a molten metal c o a t i n g  Metal  Metal  Studied  Metal Coated  Studied  Metal Coated  Cadmium  Tin  Cadmium  Mercury  Cadmium  Gallium  Lead  Mercury  Zinc  Mercury  Copper  Mercury  Zinc  Gallium  Copper  Tin  Zinc  Tin  Copper  Zinc  Tin  Mercury  Zinc  Lead  Tin  Gallium  -  -  Copper  Bismuth  -  -  THE  AIM OF PRESENT INVESTIGATION A l t h o u g h v a r i o u s k i n d s o f e x p e r i m e n t s on l i q u i d m e t a l  embrittlement  have been c a r r i e d out t o e s t a b l i s h t h e e x a c t mechanism and a s s o c i a t e d problems, none o f them p a i d s p e c i a l a t t e n t i o n t o the work h a r d e n i n g s i n g l e c r y s t a l s i n the p r e s e n c e o f s u r f a c e a c t i v e media.  c h a r a c t e r i s t i c s of  -10-  In t h i s p r e s e n t i n v e s t i g a t i o n , an attempt has been made t o e x p l a i n the l i q u i d m e t a l e m b r i t t l e m e n t i n the c o n t e x t o f t h e p r e s e n t u n d e r s t a n d i n g o f d e f o r m a t i o n t h e o r y under t h e f o l l o w i n g e x p e r i m e n t a l schemes. (1)  The  system s t u d i e d c o n s i s t s  of zinc single c r y s t a l s of f i x e d  o r i e n t a t i o n w e t t e d by mercury as a s u r f a c e a c t i v e m e t a l . (2)  The amount o f mercury used f o r c o a t i n g and time o f immersion  of  c r y s t a l s i n mercury were f i x e d . (3)  C r i t i c a l r e s o l v e d shear s t r e s s T , c  (0^)  and s t a g e B ( O g ) ,  fracture  strain  parameters  work h a r d e n i n g s l o p e i n stage A  t r a n s i t i o n s t r a i n from stage A t o B ,  ^A_J_^  T x were d e f i n e d as  and f r a c t u r e s t r e s s  t o compare t h e r e s u l t s o b t a i n e d from d i f f e r e n t e x p e r i m e n t a l  conditions.  C r i t i c a l r e s o l v e d shear s t r e s s was  determined  from t h e  at w h i c h the s h e a r s t r e s s s t r a i n curve f i r s t d e v i a t e s from because coated specimens under c e r t a i n experiment  linearity  c o n d i t i o n s f a i l before the  f u l l development o f stage A making assessment o f the v a l u e C r  c  p o l a t i n g stage A i m p o s s i b l e .  stress  by  extra-  - 11 -  I I . EXPERIMENTAL PROCEDURE A. MATERIAL  The z i n c used i n t h i s experiment was p u r c h a s e d from t h e C o n s o l i d a t e d M i n i n g and S m e l t i n g Company L i m i t e d , T r a i l , B.C., Canada. The p u r i t y o f t h e z i n c was  99-999  Commercial grade o f mercury was t r e a t e d w i t h c o n c e n t r a t e d m e r c u r i c n i t r a t e and o x i d i z e d so t h a t base m e t a l i m p u r i t i e s can be removed.  The mercury used i n t h i s experiment was m a i n l y c o n t a m i n a t e d by  z i n c , s o l d e r (specimen mounting a l l o y ) , and aluminum ( g r i p ) .  During the  o x i d a t i o n , a s i l v e r y f r o t h b e g i n s t o f o r m and a g i t a t o r s c o n t i n u a l l y f o r c e the  f r o t h t h r o u g h t h e mass o f mercury.  a layer.  The f r o t h darkens and t h i c k e n s t o  As t h e o x i d a t i o n p r o c e e d s f u r t h e r , a b l a c k powder forms on t h e  s u r f a c e and t h e f r o t h g r a d u a l l y d i s a p p e a r s , l e a v i n g a l a y e r o f d r y , b l a c k powder f l o a t i n g on b r i g h t mercury.  O x i d i z e d mercury was f i l t e r e d by  mercury f i l t e r w h i c h c o n s i s t s o f a r e s e r v o i r w i t h d i s c h a r g e a p e r t u r e a t t h e bottom. element.  Surrounding t h i s aperture i s a r i n g of gold, which i s the f i l t e r i n g F i n a l l y mercury i s f i l t e r e d by g o l d a d h e s i o n p r i n c i p l e .  Conta-  minated mercury f r o m w e t t i n g o f z i n c c r y s t a l s i s p u r i f i e d u s i n g t h e above mentioned method.  B. (i)  SPECIMEN PREPARATION Growth o f S i n g l e C r y s t a l s The s i n g l e c r y s t a l s were grown f r o m m e l t by Bridgman's  method.  E x t r u d e d z i n c w i r e t o g e t h e r w i t h seed c r y s t a l was c h a r g e d i n t o p y r e x g l a s s tube w h i c h has a c l o s e d sharp t i p a t one end.  The o t h e r end o f the p y r e x  - 12 -  mould was c o n n e c t e d t o vacuum pump t o e v a c u a t e a i r i n i t and s e a l e d o f f t o p r e v e n t o x i d a t i o n o f z i n c d u r i n g growth.  The f u r n a c e used f o r g r o w i n g  i s a v e r t i c a l type w i t h N i - C r w i r e as heat element.  crystals  A thermocouple was  i n s e r t e d h a l f w a y o f t h e f u r n a c e body and t h e t e m p e r a t u r e was c o n t r o l l e d b y WHEELCO t y p e c o n t r o l l e r . was k^O"C.  The t e m p e r a t u r e i n t h e v i c i n i t y o f t h e thermocouple  The v e r t i c a l t r a v e l l i n g r a t e o f t h e charged mould i n t h e  f u r n a c e was 35 mm/hr.  A f t e r d e t e r m i n i n g temperature d i s t r i b u t i o n o f the  f u r n a c e , t h e upper h a l f o f t h e seed c r y s t a l was p l a c e d a t m e l t i n g zone so t h a t t h e m e l t o f p o l y c r y s t a l l i n e z i n c would t u r n i n t o m o n o c r y s t a l as t h e charge moves down.  Four charged p y r e x molds were t r e a t e d as a s i n g l e b a t c h by above  mentioned t e c h n i q u e and as a r e s u l t , f o u r l o n g c r y s t a l s o f about kOcm l o n g were o b t a i n e d a t one t i m e .  To remove t h e c r y s t a l s f r o m t h e mould w i t h o u t  i n t r o d u c i n g u n d e s i r e d d e f o r m a t i o n , t h e g l a s s mould was d i s s o l v e d i n k&jo HF solution.  The t h i n o x i d e f i l m formed d u r i n g growth k e p t c r y s t a l s f r o m  a t t a c k i n g b y HF s o l u t i o n .  B a c k - r e f l e e t i o n Laue X - r a y method was a p p l i e d t o d e t e r m i n e t h e o r i e n t a t i o n o f t h e grown c r y s t a l s . t h i s i n v e s t i g a t i o n was X  Q  = h6° *  The o r i e n t a t i o n o f a l l c r y s t a l s u s e d i n 3° and 9^o = ^6° *  h°, where X  a n g l e between t h e specimen a x i s and s l i p p l a n e , a n d ^ o i the specimen a x i s and s l i p d i r e c t i o n .  s  c  i s the  "the a n g l e between  T h i s o r i e n t a t i o n i s such t h a t  slip  system o p e r a t e s a l o n g (0001) p l a n e i n t h e d i r e c t i o n o f [ 1 1 2 0 ] .  (ii)  S u r f a c e C o a t i n g o f t h e S i n g l e C r y s t a l s w i t h Mercury The specimens were p o l i s h e d b y e l e c t r o p o l i s h i n g t e c h n i q u e i n  the m i x t u r e s o l u t i o n o f 25g C r 0 , 7cc H 0 and 133cc Cone. CH C00H. 2  3  2  3  - 13 -  On removing o x i d e f i l m on t h e s u r f a c e , t h e c r y s t a l was mounted i n aluminum g r i p s w i t h s o l d e r .  O r d i n a r y s o l d e r i n g f l u x p a s t e d a t t h e end o f  t h e c r y s t a l improved w e t t i n g o f c r y s t a l s w i t h m o l t e n s o l d e r .  MICROSTOP  covered t h e exposed s o l d e r a t t h e g r i p t o a v o i d c o n t a c t between mercury and solder.  Then b o t h ends o f mounted c r y s t a l were wrapped w i t h p o l y e t h y l e n e  paper t o reduce the p o s s i b i l i t i e s o f e a r l y f a i l u r e r e s u l t i n g from a d s o p t i o n o f mercury a t t h e k i n k t h a t appears f r e q u e n t l y i n t h e v i c i n i t y o f g r i p d u r i n g deformation.  The mounted c r y s t a l w i t h p r o t e c t e d ends was p l a c e d i n a s t a i n l e s s  s t e e l j i g h o r i z o n t a l l y and t i g h t e n e d v e r y c a r e f u l l y by u s i n g two arms s t r e t c h e d out of the m i d d l e o f t h e j i g .  F i n a l l y , t h e j i g was immersed  i n t o f i x e d amount  o f c l e a n mercury c o n t a i n e d i n a p l a s t i c b o a t , and the t i m e o f immersion was measured by s t o p watch.  F i g . 1 shows t h e mounting a p p a r a t u s and s t a i n l e s s  s t e e l j i g w h i c h h o l d s mounted specimen.  The dimensions o f a mounted specimen  are shown i n F i g u r e 2 .  C.  TENSILE TESTING A screw d r i v e n INSTRON t e n s i l e t e s t i n g machine was used f o r the'  test.  The u n i v e r s a l g r i p p i n g heads were mounted below the c r o s s  t h a t w a t e r b a t h can be a t t a c h e d i n t h e h i g h temperature t e s t .  head so  The g i m b a l s  g r i p s w h i c h have two r o t a t i o n a l a x i s were used t o a c h i e v e q u i c k and smooth a l i g n m e n t o f specimen t o t h e t e n s i o n a x i s .  The s t r a i n r a t e and c h a r t speed  were f i x e d as 0.1"/min and 1.0"/min r e s p e c t i v e l y .  The t e n s i l e t e s t  results  were r e c o r d e d by a u t o g r a p h i c r e c o r d e r i n t h e form of l o a d - e l o n g a t i o n c u r v e . CT and C c e l l were used and b e f o r e p r o c e e d i n g e v e r y t e s t , t h e l o a d system was c a l i b r a t e d t o o b t a i n c o r r e c t l o a d a p p l i e d t o specimens.  - Ik  F i g . 1.  Mounting A p p a r a t u s and J i g .  GRIP 3,2  1.0  Ep 0^32  1,25  L_  2.5 SPECIMEN  POLYETHYLENE PAPER Fig. 2.  Dimensions o f Mounted C r y s t a l . ( U n i t : cm)  0,8  - 15 -  III.  A. (i)  EXPERIMENTAL RESULTS  WETTING EXPERIMENT Zn-Hg System The phase d i a g r a m o f Zn-Hg system d e t e r m i n e d b y E.A. Anderson 1 6  i s shown i n F i g . Hg-Zn  Merrury-Ziiic  B Y E . A . ANDERSON*  Atomic Percentage Mercury 20 30 AO 50 60 70 SO 90 io • I—n 1 •i  500  M  BOO  400  Boiling  L  300  Z  -  200 1 1 1 1 100 1 0 -100  a +1  400  _____  a+  r*a10  20  > " 9 9 S t  ft  f  Zn  200  p  1 1  600  30  40  50  60  -  70  its  80  Weight Percentage Mercury  6~ -38.9' 90  Hg  F i g . 3. Hg-Zn System ( f r o m M e t a l s Handbook)  The s o l u b i l i t y o f mercury i n s o l i d z i n c has n o t been e s t a b l i s h e d a c c u r a t e l y , but the  i s p r o b a b l y l e s s t h a n 1$ a t room t e m p e r a t u r e . A c c o r d i n g t o Von S i m s o n |3 phase i s h e x a g o n a l w i t h a n a x i a l r a t i o o f 2 . 0 1 . The c r y s t a l  1 7  structure  o f "Zf phase, s t a b l e o n l y below room t e m p e r a t u r e , has n o t been d e t e r m i n e d .  - 16 -  (il)  W e t t i n g Experiment w i t h P o l y c r y s t a l l i n e Z i n c Mercury i s s t r o n g l y s u r f a c e a c t i v e w i t h r e s p e c t t o z i n c .  As  a f i r s t s t e p t o e s t a b l i s h t h e r e l a t i o n a p p l y i n g t o t h e w e t t i n g o f mercury over t h e s u r f a c e o f z i n c , two groups o f p o l y c r y s t a l l i n e z i n c specimens w i t h d i f f e r e n t g r a i n s i z e were p r e p a r e d b y e x t r u s i o n a t two d i f f e r e n t t e m p e r a t u r e s . Each specimen o f t h e same group had t h e same d i m e n s i o n .  On p o l i s h i n g t h e s u r f a c e ,  each specimen was w e t t e d i n l O c c c l e a n mercury and t i m e o f immersion was r e c o r d e d by s t o p watch.'  The w e i g h t g a i n e d p e r u n i t s u r f a c e a r e a o f t h e specimen was determined b y t a k i n g  t h e w e i g h t d i f f e r e n c e between w e t t e d and unwetted  and d i v i d i n g i t b y t o t a l s u r f a c e a r e a . specimens o f s m a l l g r a i n s i z e weight g a i n e d , 1.05mg/cm . 2  (90yCt)  The r e s u l t i s g i v e n i n F i g . k.  specimen The  r e v e a l e d a maximum a t 130 sees w i t h t h e  On t h e o t h e r hand, t h e maximum w e i g h t g a i n e d by  specimens o f l a r g e r g r a i n s i z e (190>o) was s h i f t e d t o l e f t w i t h t h e v a l u e o f 2.66mg/cm a t 90 s e e s . 2  The o c c u r r e n c e o f maxima i n w e i g h t g a i n e d v s t i m e o f immersion curve i n d i c a t e s t h e e v i d e n c e o f c o u n t e r d i f f u s i o n between z i n c and mercury. A l s o t h e maxima r e v e a l e d a t d i f f e r e n t immersion t i m e i m p l i e s t h e importance o f g r a i n boundary  diffusion.  ( i i i ) W e t t i n g Experiment w i t h S i n g l e C r y s t a l Specimen Two groups o f s i n g l e c r y s t a l s grown b y d i f f e r e n t growth r a t e were used i n t h i s e x p e r i m e n t .  The c l e a n and o x i d e f r e e s u r f a c e was o b t a i n e d  by e l e c t r i c p o l i s h i n g i n t h e m i x t u r e s o l u t i o n o f 25g C r 0 , 2  133cc cone.  CH3COOH  w i t h 18 v o l t .  3  7 H_0 and CC  Then t h e c r y s t a l s were c o a t e d i n 50cc  - 18  F i g . 5.  Weight Gained p e r U n i t A r e a o f t h e S u r f a c e byS i n g l e C r y s t a l Specimens.  -  - 19  c l e a n mercury and t h e w e i g h t g a i n e d p e r u n i t s u r f a c e a r e a d e t e r m i n e d by the same t e c h n i q u e used f o r p o l y c r y s t a l l i n e specimens. Fig.  The r e s u l t i s shown i n  5.  As the case o f p o l y c r y s t a l l i n e specimens, w e i g h t g a i n e d p e r u n i t s u r f a c e a r e a vs t i m e o f immersion c u r v e s a l s o r e v e a l e d maxima.  The i d e a o f  p r e p a r i n g two groups o f m o n o c r y s t a l s by t h e d i f f e r e n t growth r a t e was  to  d e t e c t t h e e f f e c t o f d e n s i t y o f s t r u c t u r a l d e f e c t (vacancy o r d i s l o c a t i o n ) on w e t t i n g c h a r a c t e r i s t i c s .  The d i s c r e p a n c y o f maxima between t h e s e two  groups o f c r y s t a l s , however, appears t o be due t o t h e d i f f e r e n c e o f s u r f a c e c o n d i t i o n (degree o f m i c r o r e l i e f ) and not t h a t o f d e n s i t y o f s t r u c t u r a l defects.  B.  TENSILE TEST OF UNCOATED CRYSTALS The shear s t r e s s - s t r a i n curve produced by t h e s l i p on h.c.p.  m e t a l i s i l l u s t r a t e d by t h e w e l l known t h r e e s t a g e i n F i g . 6.  I n o r d e r t o i n v e s t i g a t e t h e e f f e c t o f mercury c o a t i n g on t h e deformation c h a r a c t e r i s t i c s of zinc s i n g l e c r y s t a l s , the f o l l o w i n g were d e f i n e d and (1)  parameters  studied.  The c r i t i c a l r e s o l v e d s h e a r s t r e s s  'f > c  d e t e r m i n e d from t h e s t r e s s  a t w h i c h the s h e a r s t r e s s - s t r a i n c u r v e f i r s t d e v i a t e s from l i n e a r i t y . (2)  The t r a n s i t i o n s t r a i n  Y  A  g> from s t a g e A t o s t a g e B d e t e r m i n e d by  t h e s t r a i n a t w h i c h the l i n e a r s t a g e A ends. (3)  The work h a r d e n i n g s l o p e s  and Qg w h i c h were measured from t h e s l o p e s  o f the s h e a r s t r e s s - s t r a i n curve i n s t a g e A and B. (k)  The f r a c t u r e s t r e s s 'Xt and s t r a i n  "tfi a t w h i c h t h e specimen f a i l e d .  -  - 2.1  Three uncoated specimens were t e s t e d a r room temperature t o o b t a i n standard v a l u e s o f above mentioned parameters and t h e n compared w i t h t h e r e s u l t s o f subsequent e x p e r i m e n t s .  The r e s o l v e d s h e a r s t r e s s - s h e a r s t r a i n  curves were o b t a i n e d from t h e l o a d - e l o n g a t i o n c h a r t u s i n g t h e f o r m u l a by B o a s . 1 8  given  The r e l a t i o n s a r e g i v e n by  T=  l  sin X  A  C  io  (  ./ A  f  - Sin ^  1 ^ V ±>  Q  ....-5  )  K  Q  and  where P i s t e n s i l e l o a d , A i s o r i g i n a l a r e a o f c r o s s s e c t i o n , 1 gauge l e n g t h , 1 i s gauge l e n g t h a f t e r d e f o r m a t i o n , meaning as d e f i n e d b e f o r e .  i s initial  D  X_ and  have t h e same  F i g . 7 shows r e s o l v e d s h e a r s t r e s s - s t r a i n  curves  of uncoated c r y s t a l s f o r t h e t e n s i l e t e s t performed a t room temperature w i t h a s t r a i n r a t e o f 0.1"/min.  The r e s u l t s a r e summarized i n Table I I .  TABLE I I The v a l u e s o f parameters o b t a i n e d by t e n s i l e t e s t o f uncoated c r y s t a l s Spec. f ( K g / c m ) Q ( K g / c m 2 / i . s . ) 1A-B(*)T _ (Kg/cm2) No, 2  A  A  c  zxs-x-i  1.71  10.3  zxs-c-3  1.69  11.2  ZX3-K-2  I.76  10.5  150  135  B  0 (Kg/cm2/ E  19  62.5  20  63.0  19  80.0  u < S o  )  Mi) 413  T ( Kg/cm ) 2  t  101  103 356  80  -  C.  THE EFFECT OF TIME OF IMMERSION ON THE WORK HARDENING CHARACTERISTICS A s e r i e s o f experiments were done t o i n v e s t i g a t e t h e e f f e c t o f  immersion time on the work h a r d e n i n g c h a r a c t e r i s t i c s under the premise  that  amount o f mercury p i c k e d up by z i n c m o n o c r y s t a l s i n c r e a s e s w i t h immersion time.  I n t h i s s e r i e s o f e x p e r i m e n t s , b o t h ends o f the c r y s t a l n e a r g r i p s were  not p r o t e c t e d and d u r i n g t h e immersion, t h e y were a l s o c o a t e d by mercury. amount o f mercury used was 50cc. t e s t i n g was f i x e d f o r 5 mins.  The  The exposure time between w e t t i n g and  Then, the c o a t e d specimens were t e s t e d a t room  temperature w i t h a s t r a i n r a t e o f 0.1"/min.  More t h a n h a l f o f the  f a i l e d a t k i n k bands i n t h e v i c i n i t y o f g r i p s .  The mounting a l l o y  specimens (solder)  exposed t o mercury d u r i n g c o a t i n g adsorbed more mercury t h a n c e n t r a l p a r t o f the c r y s t a l so t h a t k i n k s formed near the g r i p s were i n more f a v o u r a b l e c o n d i t i o n f o r heavy mercury  coating.  T a b l e I I I shows the t e s t i n g r e s u l t s when  time of immersion changed from 2 sees t o 8 s e e s .  F r a c t u r e s t r e s s and  were not i n c l u d e d i n the t a b l e because unexpected e a r l y f a i l u r e o f at g r i p s r e v e a l e d wide s p r e a d i n g r e s u l t s w h i c h have no v a l u e o f  strain  specimens  comparison.  The r e s u l t s can be summarized as f o l l o w s . (1)  C r i t i c a l r e s o l v e d s h e a r s t r e s s was  i n c r e a s e d by mercury c o a t i n g and  dependent on time of immersion. (2)  Work h a r d e n i n g s l o p e i n stage A was  i n c r e a s e d compared t o the uncoated  c r y s t a l s , but t h e i n c r e a s e was almost i n s e n s i t i v e t o time o f immersion. (3)  T r a n s i t i o n s t r a i n from stage A t o B had a d e c r e a s i n g tendency w i t h time of  immersion.  (k)  The change o f t r a n s i t i o n s t r e s s ''£''-B 'was q u i t e random.  (5)  Work h a r d e n i n g s l o p e i n stage B i n c r e a s e d s l i g h t l y b u t e a r l y f a i l u r e of  A  specimens w i t h an immersion time beyond 8 sees made i t obscure t o p r o v e .  - 24 -  TABLE I I I The E f f e c t o f Immersion Time on t h e Work Hardening C h a r a c t e r i s t i c s  Specimen T No.  (Kg/cm ) 2  c  9 (Kg/cm2/u.s.) * A - B ( * ) ?A_B(Kg/cm2) 0 (Kg/cm ^.s.) Time o f Immersion (sees) 2  A  B  ZXS-W-3  1.76  10.0  125  16  86  2  ZXS-H-2  1.25  12.2  125  23  70  2  ZNX-F-2  1.8  12.0  115  20  50  2  ZXS-J-1  1.77  10.0  115  16  75  4  ZXS-G-3  1.79  13.0  125  20  80  4  ZXII-E-1  l.8l  8.5  125  13  60  4  ZXS-W-2  1.83  11.4  110  16  -  6  ZXS-G-1  1.84  11.8  115  19  -  6  ZX0-E-2  1.82  11.0  125  17  85  6  ZXS-U-1  1.96  12.3  100  15  -  8  ZXS-D-1  2.0  12.0  -  -  -  8  ZXII-B-2  2.03  -  -  -  -  8  D.  THE EFFECT OF EXPOSURE TIME I N AIR AFTER MERCURY COATING ON THE WORK HARDENING CHARACTERISTICS. D i f f u s i o n i s a t i m e dependent p r o c e s s .  T h e r e f o r e exposure o f  c o a t e d specimens i n a i r f o r a c e r t a i n time s h o u l d i n t e n s i f y t h e e f f e c t o f e m b r i t t l e m e n t i f t h e e m b r i t t l e m e n t i s due t o t h e d i f f u s e d s u r f a c e l i q u i d metal i n t o the c r y s t a l s .  active  - 25 -  I n t h i s e x p e r i m e n t , h o t h ends o f the specimen near g r i p s were p r o t e c t e d by w r a p p i n g them w i t h p o l y e t h y l e n e paper.  A t the same t i m e , mounting  a l l o y exposed a t g r i p s was c o v e r e d by MICROSTOP t o keep the a l l o y from mercury. Then, t h e specimens were c o a t e d w i t h mercury by immersing them i n t o 50cc c l e a n mercury f o r 8 sees and t e s t e d a t room temperature w i t h a s t r a i n r a t e o f 0.1"/min„ F i g . 8-9  show t h e r e s u l t s when exposure time was  t o 15 mins'.  i n c r e a s e d g r a d u a l l y from 5 mins  The e f f e c t o f exposure t i m e i n a i r a f t e r c o a t i n g on t h e work h a r d e n i n g  c h a r a c t e r i s t i c s i s g i v e n i n T a b l e TV-.  The r e s u l t s can be summarized as f o l l o w s : (1)  The mercury c o a t i n g i n c r e a s e d "X the i n c r e a s e was dependent  (2)  c  compared t o t h a t o f u n c o a t e d specimens  and  on t i m e o f exposure i n a i r a f t e r c o a t i n g .  Work h a r d e n i n g s l o p e i n stage A was i n c r e a s e d compared t o u n c o a t e d c r y s t a l s w i t h d e c r e a s i n g tendency t o a v a l u e s i m i l a r t o t h a t of u n c o a t e d crystals as the time o f exposure i n c r e a s e s .  (3)  T r a n s i t i o n s t r a i n from s t a g e A t o B was r e m a r k a b l y d e c r e a s e d w i t h time of exposure and t h e s t a g e B was e l i m i n a t e d a f t e r 30 mins. exposure i n a i r . F i g . 10 in  (k)  shows t h e r e d u c t i o n o f f r a c t u r e s t r a i n w i t h the t i m e of exposure  air.  The t r a n s i t i o n s t r e s s T _ g A  specimen.  was i n the neighbourhood o f that o f uncoated  However t h e s e v a l u e s were g e n e r a l l y h i g h e r t h a n the c o r r e s p o n d i n g  stresses of t h e same amount o f s t r a i n i n u n c o a t e d specimens. (5)  Work h a r d e n i n g s l o p e i n s t a g e B was a l s o i n c r e a s e d compared to uncoated crystals.  0  0,5  1,0  1,5 SHEAR  F i g . 8.  2,0 STRAIN  Y  2,5  3,0  Shear S t r e s s - S t r a i n Curves f o r C o a t e d C r y s t a l s T e s t e d i n T e n s i o n a t Room Temperature (Time o f Exposure i n A i r a f t e r C o a t i n g : 5 mins)  35 o ,  0  0,5  1,0  1,5 SHEAR  F i g , 9.  STRAIN  2,0  2,5  3,0  *  Shear S t r e s s - S t r a i n Curves f o r Coated C r y s t a l s T e s t e d i n T e n s i o n a t Room Temperature (Time o f Exposure i n A i r a f t e r C o a t i n g : 10 and 15 mins.  TABLE IV The E f f e c t o f Exposure Time i n A i r a f t e r Mercury C o a t i n g on Work Hardening C h a r a c t e r i s t i c s  Specimen No.  T  (Kg/cm ) 2  c  6 (kg/cm /u.s.) 2  A  tf - (*) A  B  f _ (Kg/cm2) A  B  f3 (Kg/cm u.s.) If (Kg/cm ) 2  Time o f Exposure (min)  2  B  ZXI-N-3  2.00  13.3  110  17  95  104.1  304  5  ZXS-F-3  1.99  17.2  95  21  75  100.0  254  5  ZXS-F-2  1.95  17.2  100  22  70  97-6  267  5  ZXS-N-2  2.03  12.0  100  16  95  97-0  267  10  ZXI-0-4  2.03  16.0  90  21  70  59-0  173  15  ZXI-0-2  2.06  17.1  80  21  65  61.6  179  15  ZXI-M-3  2.07  12.6  -  -  -  13.2  62  30  ZXI-M-2  2.12  14.3  -  -  -  14.5  72  30  ZXI-L-4  2.12  13.6  -  -  -  8.7  33  60  ZXI-0-3  2.11  9.7  -  ---  -  6.1  38  60  - 29  0  10  20  30  40  EXPOSURE TIME  F i g . 10.  E.  50  60  70  (MIN)  The E f f e c t o f Exposure Time a f t e r C o a t i n g on F r a c t u r e S t r a i n .  THE EFFECT OF PRESTRAIN AND MERCURY COATING ON THE WORK HARDENING CHARACTERISTICS. The s t r u c t u r a l d e f e c t s i n c r e a s e as d e f o r m a t i o n  proceeds.  i n t e r a c t i o n s between s t r u c t u r a l d e f e c t s and d i f f u s e d s u r f a c e a c t i v e m e t a l causes t h e e m b r i t t l e m e n t , hardening  I f the liquid  t h e amount o f p r e s t r a i n s h o u l d m o d i f y t h e work  c h a r a c t e r i s t i c s o f zinc monocrystal  c o a t e d w i t h mercury.  A f t e r c l e a n c r y s t a l s were p r e s t r a i n e d up t o c e r t a i n amount o f shear s t r a i n , they were removed from INSTRON and b o t h ends o f c r y s t a l s were p r o t e c t e d  - 30  b e f o r e mercury c o a t i n g .  Then t h o s e specimens w i t h p r o t e c t e d ends were immersed  i n 50cc mercury f o r 8 sees. 5)mm  exposure i n a i r .  Test was  F i g . 11-13  i n c r e a s e d amount o f p r e s t r a i n .  resumed a f t e r 10 min w r a p p i n g and  show t h e The  The (1)  r e s u l t s can be  (2)  P r e s t r a i n and If  , work h a r d e n i n g s l o p e i n stage  s i n c e the t e s t s were  The  change o f If  r  r e s u l t s show t h a t  - if  was  p r e s t r a i n but a f t e r t h a t dropped d r a s t i c a l l y . Ik.  A,  mercury c o a t i n g a f f e c t e d the amount o f e l o n g a t i o n markedly.  decreases w i t h p r e s t r a i n .  in Fig.  on  as t h o s e o f uncoated c r y s t a l s .  7f stands f o r the amount of p r e s t r a i n , the " ps r >  t o 100$  mercury c o a t i n g  follows:  t r a n s i t i o n s t r a i n "2^-15 were not a f f e c t e d  performed under the same c o n d i t i o n s  gradually  V.  summarized as  C r i t i c a l r e s o l v e d s h e a r s t r e s s , T" 0^ and  shear s t r e s s - s t r a i n curve w i t h  e f f e c t o f p r e s t r a i n and  d e f o r m a t i o n parameters i s g i v e n i n T a b l e  subsequent  not  if  „f  "3V pS  s i g n i f i c a n t up  T h i s r e l a t i o n i s shown  -  - 31 -  0,2  0  0,4  0,8  0,6  SHEAR  1,0  STRAIN  F i g . 11. Shear S t r e s s - S t r a i n Curves f o r P r e s t r a i n e d and C o a t e d C r y s t a l s T e s t e d i n T e n s i o n a t Room Temperature.  TABLE V. The E f f e c t o f p r e s t r a i n and Mercury C o a t i n g on Work H a r d e n i n g C h a r a c t e r i s t i c s  Specimen T No.  C  (Kg/cm ) © (Kg/cm /u.s.) 2  2  A  TTA-B(*)  T _ ( K g / c m ) >X (Kg/cm ) 2  A  B  Amount($) of Prestrain  2  f  ZXS-D-3  1.81  10.0  -  -  16.2  81  30  ZXS-D-2  1.69  10.3  -  -  16.3  91  30  ZXI-P-2  1.67  11.0  -  -  19.2  151  100  ZXS-L-2  1.78  13.0  -  -  26.2  153  105  ZXI-P-4  1.63  10.0  125  17.5  40.8  184  162  ZXI-P-3  I.65  10.0  i4o  18.0  37-7  191  165  40  O  ZXI—  P-2  SHEAR F i g . 12.  STRAIN  Shear S t r e s s - S t r a i n Curves f o r P r e s t r a i n e d and Coated C r y s t a l s T e s t e d i n T e n s i o n a t Room Temperature.  ro  SHEAR F i g . 13.  STRAIN  TT  Shear S t r e s s - S t r a i n Curves f o r P r e s t r a i n e d T e n s i o n a t Room Temperatures.  and Coated C r y s t a l s T e s t e d i n  1  0  20  60 AMOUNT OF  F i g . Ik.  140 Tf_ ( % P  180  )  The E f f e c t o f P r e s t r a i n and Mercury C o a t i n g  °  F.  100 PRESTRAIN  n  * f "^sp  THE EFFECT OF MERCURY COATING AND HIGH TEMPERATURE ON THE WORK HARDENING CHARACTERISTICS. The importance o f s u r f a c e and l a t t i c e d i f f u s i o n i s e v i d e n t from  the experiments o f exposure time and i t has become v a l u a b l e t o e s t a b l i s h t h e e f f e c t of higher temperature.  D i f f u s i o n p r o c e s s e s w i l l be a c c e l e r a t e d a t  h i g h e r temperature and more d r a s t i c e m b r i t t l e m e n t s h o u l d be r e s u l t e d . In o r d e r t o a s s e s s t h e e f f e c t o f mercury c o a t i n g and h i g h e r  - 35 -  temperature on the work h a r d e n i n g c h a r a c t e r i s t i c s o f z i n c m o n o c r y s t a l s , t h e f o l l o w i n g e x p e r i m e n t a l p r o c e d u r e s were i n v o l v e d .  The specimens w i t h p r o t e c t e d  ends were c o a t e d w i t h mercury by immersing them i n t o 50cc c l e a n mercury f o r 8 sees.  A f t e r 5 mins exposure i n a i r , the c o a t e d specimen was brought t o  INSTRON and hot w a t e r b a t h was p l a c e d around the specimen.  The w a t e r b a t h  was h e a t e d by v e r t i c a l type immersion h e a t e r by c o n t r o l l i n g t h e i n p u t power with a variac.  The temperature was measured w i t h mercury thermometer e v e r y  t h r e e minutes.  The temperature v a r i a t i o n was n e g l i g i b l e c o n s i d e r i n g s h o r t t i m e  of t e s t i n g r e s u l t i n g from e a r l y f a i l u r e o f specimens. ( T = t° ± 1°).  Coated  specimens were h e l d a t d e s i r e d h i g h temperature f o r 5 mins and t h e n hot w a t e r b a t h was r e p l a c e d by c o l d w a t e r b a t h t o c o o l the specimens down t o room temperature a g a i n . of 0.1"/min.  Then t h e specimens were p u l l e d by INSTRON w i t h a s t r a i n r a t e  The e f f e c t o f mercury c o a t i n g and h i g h e r t e m p e r a t u r e on the work  h a r d e n i n g c h a r a c t e r i s t i c s i s g i v e n i n Table V I .  TABLE V I The E f f e c t o f Mercury C o a t i n g and P r e h e a t i n g on Room Temperature D e f o r m a t i o n C h a r a c t e r i s t i c s Specimen r (Kg/cm ) 0 (Kg/cm /u.s.) *A-B(*) 0 B (Kg/cm A s . ) r ( K g c m ) No. 2  2  2  2  f  A  c  y  r ($) f  Preheat Temp. °C  ZXI-V-2  2.09  12.0  -  -  13.4  85.7  50  ZXI-V-3  2.20  11.0  -  -  13.2  89.7  50  ZXI-W-3  2.30  15.7  -  -  7-5  30.0  75  ZXI-V-1  2.24  13.8  -  -  9.3  44.0  75  ZXI-Y-3  2.52  -  -  -  4.6  6.7  95  ZXI-Y-2  2.46  -  -  -  5-5  9.8  95  - 36 -  The r e s u l t s can be summarized as f o l l o w s : (1)  The stage B was c o m p l e t e l y e l i m i n a t e d i n these, experiments severe e m b r i t t l e m e n t e f f e c t . t h e temperature  (2)  The f r a c t u r e  indicating  C r i t i c a l shear s t r e s s ^ was i n c r e a s e d as  increased.  s t r e s s and s t r a i n were decreased w i t h t h e t e m p e r a t u r e .  F i g . 15 shows t h e e f f e c t o f mercury c o a t i n g and h i g h temperature on fracture (3)  strain.  There was a tendency such t h a t increased.  i n c r e a s e s as t h e h e a t i n g  temperature  However, t h e e a r l i e r f a i l u r e s r e s u l t i n g from 5 min. h o l d i n g  a t 95°C e l i m i n a t e d t h e s u f f i c i e n t appearance of t h e r e s u l t  o f stage A making  difficult.  20 F i g . 15.  60 40 TEMPERATURE The E f f e c t o f Mercury C o a t i n g and H i g h e r Temperatures on F r a c t u r e S t r a i n .  assessment  - 37 -  SUMMARY OF RESULTS The weight g a i n e d v s immersion t i m e c u r v e s o b t a i n e d from mercury  coating  e x p e r i m e n t s show maxima i n b o t h p o l y c r y s t a l l i n e and m o n o c r y s t a l specimens. T h i s i m p l i e s t h e e v i d e n c e o f h i g h c o u n t e r d i f f u s i o n between z i n c and mercury when t h e y a r e i n c o n t a c t w i t h each o t h e r . In non-coated c r y s t a l s , t h e c r i t i c a l r e s o l v e d s h e a r s t r e s s i s 1.72Kg/cm and X  0  —  = 3'05 x 10  i s observed f o r t h e c r y s t a l o r i e n t a t i o n o f  = 46 * 3° and9\_ = 46 * 4° .  ( XQ. = 1  8  2  Kg/cm by J i l l s o n 2  1 9  The r e l a t i o n between 0  A  and Q  B  i s Qg = 60 . A  ).  The mercury c o a t i n g i n c r e a s e s c r i t i c a l r e s o l v e d s h e a r s t r e s s ( T  = 1.99Kg/cm  2  c  f o r 8 sees immersion and 5 mins exposure t i m e i n a i r ) and t h e i n c r e a s e i s dependent o f exposure time i n a i r a f t e r c o a t i n g . The work h a r d e n i n g s l o p e s ( 0 and ©g) a r e i n c r e a s e d b y mercury c o a t i n g and A  exposure i n a i r b e f o r e t e s t i n g . transition strain  ^  B  Under t h e same e x p e r i m e n t a l c o n d i t i o n s ,  i s d e c r e a s e d remarkably and t h e s t a g e B i s e l i m i n a t e d  a f t e r 30 mins exposure i n a i r .  A l s o f r a c t u r e s t r e s s and s t r a i n a r e  d e c r e a s e d w i t h exposure time i n a i r . The p r e s t r a i n and mercury c o a t i n g cause t h e e a r l i e r f a i l u r e o f c r y s t a l s . The r e d u c t i o n o f if ~- If i sp  (  = amount o f p r e s t r a i n ) i s n o t s i g n i f i c a n t sp  up t o 100$ p r e s t r a i n and a f t e r t h a t drops  drastically.  When c o a t e d c r y s t a l s a r e t r e a t e d a t e l e v a t e d t e m p e r a t u r e s , i n c r e a s e d c r i t i c a l r e s o l v e d shear s t r e s s i s observed.  A l s o h i g h temperature t r e a t m e n t  e l i m i n a t e s stage B, and t h e f r a c t u r e s t r e s s and s t r a i n a r e reduced as t h e h e a t i n g temperature  increases.  H.  REPRODUCIBILITY OF RESULTS T y p i c a l of e x p e r i m e n t s w i t h s i n g l e c r y s t a l s , the p r e s e n t r e s u l t s  showed a s c a t t e r of * 1 5 $ i n most of the measured p a r a m e t e r s . a minimum of two and  Accordingly,  specimens were t e s t e d under g i v e n e x p e r i m e n t a l c o n d i t i o n s ,  the r e s u l t s quoted f o r each c o n d i t i o n a r e t h e a r i t h m e t i c mean o f a l l  tests.  - 39 -  IV.  METALLOGRAPHIC OBSERVATIONS  An attempt has been made t o observe t h e s l i p markings o f mercurycoated c r y s t a l s w h i c h were deformed under v a r i o u s e x p e r i m e n t a l c o n d i t i o n s . Fig. at  16 shows t h e s l i p l i n e s o f an uncoated c r y s t a l  room t e m p e r a t u r e .  Wide d e f o r m a t i o n t w i n bands a r e o b s e r v e d .  deformed The wavy  c h a r a c t e r i s t i c s o f s l i p l i n e s a r e t h e e v i d e n c e o f dynamic r e c o v e r y d u r i n g t h e d e f o r m a t i o n r e s u l t i n g from t h e c l i m b o f edge d i s l o c a t i o n s . S m a l l humps, w h i c h a r e t e n s i l e k i n k "embryos", a r e observed as a t A i n F i g . 16.  The causes o f t h e s e humps may be e i t h e r t h e s t r e s s  c o n c e n t r a t i o n on p i t s and t r a p p e d o x i d e o r n o n - u n i f o r m d i s t r i b u t i o n o f t e n s i l e stress across s l i p planes. Fig.  17-21 show t h e s u r f a c e o f deformed c r y s t a l s c o a t e d w i t h  mercury when t i m e o f exposure i n a i r a f t e r c o a t i n g i n c r e a s e s from 5 mins. t o 60 mins.  A t t h e b e g i n n i n g , the s i z e and number o f embryos i n c r e a s e s w i t h  exposure t i m e u n t i l t h e time reaches 15 mins.  A f t e r t h a t we observe  and s m a l l e r embryos on t h e s u r f a c e o f deformed c r y s t a l s .  fewer  This behaviour i s  u n d e r s t a n d a b l e s i n c e t e n s i l e k i n k embryos s h o u l d o c c u r a f t e r s u b s t a n t i a l s t r a i n , and t h e reduced d u c t i l i t y  t h a t r e s u l t s from l o n g exposure t o mercury l i m i t s  their  formation. Fig.  22-23 show t h e d e f o r m a t i o n markings o f c o a t e d c r y s t a l s t e s t e d  at room temperature a f t e r t h e y were t r e a t e d a t e l e v a t e d temperature (50°C and 75°C). We observe w e l l developed embryos on t h e s u r f a c e o f t h e c r y s t a l w h i c h was t r e a t e d at t h e l o w e r t e m p e r a t u r e .  T h i s c r y s t a l has a f a i r amount o f d u c t i l i t y .  However,  F i g . 16.  Z X I - I - 3 x 230 (Uncoated and T e s t e d a t Room  F i g . 17.  Temperature).  ZXI-N-3 x 230 (Coated and T e s t e d a t Room Temperature • Time o f Exposure i n A i r ; 5 mins.)  - kl -  F i g . 18.  ZXI-N-2 x 230 (Coated and T e s t e d a t Room Temperature. Time o f Exposure i n A i r : 10 mins.)  F i g . 19. Z X I - 0 - 4 x 230 (Coated and T e s t e d a t Room Temperature. Time o f Exposure i n A i r : 15 mins.)  - 1+2 -  F i g . 20. ZXI-M-2 x 230 (Coated and Tested at Room Temperature. Time of Exposure i n A i r : 30 mins.)  F i g . 21. ZXI-0-3 x230 (Coated and Tested at Room Temperature. Time of Exposure in A i r : 60 mins.)  - 43 -  F i g . 2 2 . ZXI-V-2 x 230 (Coated, 5 min. Exposure i n A i r , 5 m i n . i n 50°C B a t h and Quench t o Room Temperature Room Temperature T e s t . )  F i g . 2 3 . ZXI-V-1 x 230 (Coated, 5 min. Exposure i n A i r , 5 min. i n 75°C B a t h and Quench t o Room Temperature. Room Temperature T e s t . )  - kk  the r e d u c t i o n o f d u c t i l i t y due t o t h e h i g h e r temperature the f o r m a t i o n o f embryos compared t o l o w e r temperature  treatment e l i m i n a t e s  t r e a t e d one.  F r a c t u r e s u r f a c e s were a l s o c a r e f u l l y examined under t h e microscope t o d e t e c t any e v i d e n c e s o f c r a c k i n i t i a t i o n and p r o p a g a t i o n . the i n i t i a t i o n and p r o p a g a t i o n o f c r a c k d e v e l o p e d  i n t h e uncoated  c r a c k was i n i t i a t e d on (0001) m a t r i x and propagated Fig.  F i g . 2k shows crystal.  A  a l o n g (0001) t w i n .  25-27 show c r a c k s f o r c o a t e d c r y s t a l s w h i c h were i n i t i a t e d a t k i n k bands  and propagated  along b a s a l plane.  R e l e v a n t mechanisms w i l l be c o n s i d e r e d i n  the d i s c u s s i o n p a r t .  Fig.  2k.  Crack I n i t i a t e d by Coalescence o f D i s l o c a t i o n s on M a t r i x B a s a l P l a n e Propagates a l o n g B a s a l Plane i n Twin x 230.  Fig. 26.  Crack Initiated at Tensile Kink.  Fig. 27.  Cracks Initiated at Tensile Kinks.  - 46  -  V. DISCUSSION A. WETTING CHARACTERISTICS AND  DIFFUSION OF MERCURY IN ZINC  S i n c e the r e d u c t i o n o f t h e m e c h a n i c a l s t r e n g t h and p l a s t i c i t y o f z i n c m o n o c r y s t a l s r e s u l t s from mercury c o a t i n g , i t has become n e c e s s a r y t o pay a t t e n t i o n t o the r o l e p l a y e d by w e t t i n g and (i)  diffusion.  Wetting C h a r a c t e r i s t i c s As a p r i m a r y guide from t h e thermodynamics o f t h e w e t t i n g o f s o l i d  s u r f a c e s by l i q u i d , we d e r i v e t h a t a n e c e s s a r y c o n d i t i o n f o r s p r e a d i n g i s  r  >  s  -3L  7  where if g i s the s u r f a c e energy o f s o l i d and }f*^ i s t h a t o f l i q u i d  (see  Appendix I ) . There i s s i z e a b l e d i f f e r e n c e o f s u r f a c e energy between  mercury  and z i n c (476  satisfies  ergs/cm  2  f o r H g ° and 859 e r g s / c m 2  2  for zinc  2 1  ) , which  the c o n d i t i o n o f w e t t i n g . (ii)  The D i f f u s i o n o f Mercury i n Z i n c The w e i g h t g a i n e d v s time o f immersion curve f o r p o l y c r y s t a l l i n e  specimens, when t h e y a r e immersed i n t o f i x e d amount o f mercury, from t h a t o f m o n o c r y s t a l s . roles i n diffusion.  i s quite different  This implies that s t r u c t u r a l d e f e c t s p l a y important  The w e i g h t g a i n e d v s time o f immersion c u r v e s f o r b o t h  p o l y c r y s t a l l i n e and m o n o c r y s t a l specimen have r e v e a l e d maxima i n d i c a t i n g e v i d e n t c o u n t e r d i f f u s i o n between mercury and z i n c .  At f i r s t the weight gained  i n c r e a s e d as the time of immersion up t o t h e maximum p o i n t .  During t h i s period,  the weight g a i n e d i s l a r g e r t h a n t h e l o s s o f z i n c r e s u l t i n g from c o u n t e r d i f f u s i o n i n t o mercury.  A f t e r t h e maximum, the l o s s o f z i n c i n t o t h e mercury  over the w e i g h t g a i n e d .  predominates  C o n s i d e r i n g t h e d e n s i t y d i f f e r e n c e between mercury  and  - 4? -  z i n c , the o c c u r r e n c e o f maxima i n w e t t i n g experiments p r o v e s t h e f a c t t h a t the d i f f u s i o n o f z i n c i n t o mercury appears t o be v e r y f a s t .  The w e t t i n g experiments w i t h s i n g l e c r y s t a l s have a l s o r e v e a l e d maxima.  However, the maxima o c c u r r e d a t e a r l i e r t i m e s o f immersion  of p o l y c r y s t a l l i n e  than t h a t  specimen.  Various attempts designed t o e x p l a i n the d i f f e r e n c e s i n weight g a i n e d and maxima t i m e s were not s u c c e s s f u l because o f t h e c o m p l i c a t e d v a r i a b l e s i n v o l v e d ( g r a i n boundary, c o n c e n t r a t i o n o f s t r u c t u r a l d e f e c t s and degree o f micro r e l i e f  etc.).  D u r i n g the t e n s i l e d e f o r m a t i o n , microscopic s u r f a c e s t e p s w i l l appear on t h e s u r f a c e o f c r y s t a l due t o t h e s l i p r e v e a l i n g new  surface of b a s a l planes.  Mercury c o a t e d over the s u r f a c e o f c r y s t a l s w i l l m i g r a t e on t h e newly b a s a l p l a n e s t e p s t o reduce t h e o v e r a l l s u r f a c e energy  (a) Fig.  28.  (b)  exposed  (see F i g . 28).  (c)  Mercury M i g r a t i o n t o Newly Exposed B a s a l P l a n e D u r i n g D e f o r m a t i o n , (a) U n i f o r m C o a t i n g b e f o r e T e s t (b) Exposure o f New B a s a l P l a n e Free from Mercury (c) Mercury M i g r a t i o n t o Newly Exposed B a s a l P l a n e by S u r f a c e D i f f u s i o n .  - 48  T h i s m i g r a t i o n i s a c h i e v e d by s u r f a c e d i f f u s i o n . P l e t e n e v a and  Fedoseeva  determined t h e c o e f f i c i e n t of s u r f a c e d i f f u s i o n o f mercury on z i n c measuring  by  the r a t e o f moving f r o n t o f mercury on t h e s u r f a c e o f v e r t i c a l l y  clamped z i n c specimen.  T h i s measurement s a t i s f i e d a d i f f u s i o n a l r e l a t i o n  i n w h i c h t h e h e i g h t o f mercury r i s e was root of the time.  d i r e c t l y p r o p o r t i o n a l t o the  The determined v a l u e i s 2.48  x 10  2  square  cm /sec a t 20°C 2  which i s much f a s t e r t h a n the c o e f f i c i e n t o f b u l k d i f f u s i o n i n z i n c (0.2.3 x 1 0 "  1 1  cm /sec a t 20°C). 2  In l a t t i c e d i f f u s i o n , s t r u c t u r a l d e f e c t s , ( d i s l o c a t i o n sub-boundary) p l a y i m p o r t a n t r o l e .  Love  2 3  has proposed  and  an adequate model  f o r d i s l o c a t i o n pipe d i f f u s i o n i n which d i f f u s i o n occurs along the l i n e  of  vacant s i t e s l y i n g a d j a c e n t t o t h e edge o f e x t r a i n s e r t e d p l a n e i n an edge dislocation  (see Appendix I I ) .  T h e r e f o r e mercury atoms c o a t e d over the  surface w i l l d i f f u s e through d i s l o c a t i o n p i p e s .  As t h e d e f o r m a t i o n  proceeds  more s t r u c t u r a l d e f e c t s can he e v o l v e d and enhanced d i s l o c a t i o n p i p e d i f f u s i o n is  expected.  B.  THE EFFECT OF MERCURY COATING- ON THE CRITICAL RESOLVED SHEAR STRESS OF ZINC SINGLE CRYSTAL I n c o n s i d e r i n g t h e cause o f i n c r e a s e d c r i t i c a l r e s o l v e d s h e a r  of amalgamated c r y s t a l s , t h e f o l l o w i n g  three e f f e c t s are r e l e v a n t s u b j e c t s t o  be d i s c u s s e d . (i) (ii) (iii)  Dislocation Surface drag  egress  effect  effect  Surface anchoring  stress  effect  -  - k  A c c o r d i n g t o the f o r the (i)  f o l l o w i n g arguments, the f i r s t two  e f f e c t s can not  9  account  cause of i n c r e a s e d c r i t i c a l r e s o l v e d shear s t r e s s .  D i s l o c a t i o n Egress E f f e c t A h a r r i e r r e s u l t i n g from the  change o f s u r f a c e c o n d i t i o n would  e x p e c t e d t o have an e f f e c t on the motion o f d i s l o c a t i o n s and we t h i s e f f e c t the  " d i s l o c a t i o n egress e f f e c t " .  p u l l an edge d i s l o c a t i o n out accompanying the by F r a n k  2 4  of the  f o r m a t i o n o f new  when s u r f a c e s are  The  s u r f a c e i s r e s i s t e d by the work  surface area.  clean.  He  egress of d i s l o c a t i o n s under t h e i r own by the  shall  be  call  image f o r c e t e n d i n g t o  T h i s e f f e c t has  came t o the  image f o r c e .  done  been c o n s i d e r e d  conclusion that,  f o r l e a d , most m e t a l l i c c r y s t a l s u r f a c e s s h o u l d o f f e r no  resistance  T h i s i d e a was  except to  the  established  f a c t t h a t the energy o f a d i s l o c a t i o n l o c a t e d n e a r the s u r f a c e i s always  g r e a t e r t h a n would be a s s o c i a t e d w i t h the newly exposed s u r f a c e caused by of the  dislocation.  is I . 9 8  x 10  I n the  case o f z i n c , the  erg/cm ( if = s u r f a c e energy and  5  energy of a d i s l o c a t i o n a few I n f a c t , the coating  s u r f a c e energy  surface r e s i s t i n g force,  o f a z i n c c r y s t a l was  reduced by the  making i t e a s i e r f o r d i s l o c a t i o n s t o e g r e s s out  o f the  x  egress  if b  b= B u r g e r ' s v e c t o r ) and  atoms away from the s u r f a c e i s 2 . 6 3  mercury c o a t i n g s s h o u l d have reduced the  the  1 0 erg/cm. 5  mercury  surface.  Therefore,  c r i t i c a l r e s o l v e d shear s t r e s s i f we  c o n s i d e r the d i s l o c a t i o n e g r e s s e f f e c t o n l y . (ii)  -  S u r f a c e Drag E f f e c t Any  resistance  t o the  f o r m a t i o n o f new  s u r f a c e or shear a t the  would be e x p e c t e d t o have an e f f e c t t o the passage of the e f f e c t w i l l be termed the  " s u r f a c e d r a g effect'.  dislocations.  C o n s i d e r the p o s s i b l e  surface This  effect  -  of such a s u r f a c e drag on the o p e r a t i o n o f a F i s h e r s i n g l e - e n d e d  surface  50  source  as shown i n F i g . 29.  F i g . 29.  F i s h e r Single-Ended  At the c r i t i c a l s t r e s s OT  Q  Source.  t o operate a s i n g l e - e n d e d  f o r c e a c t i n g a t the d r a g p o i n t i s g i v e n  m cb l  Gb  _  i f b where  o f l e n g t h 1,  the  by  2  where G i s shear modulus and b i s B u r g e r ' s v e c t o r . equal to  source  The  s u r f a c e drag f o r c e i s  7f i s the s u r f a c e f r e e energy o f the c r y s t a l .  The  ratio,  q, o f the f o r c e a c t i n g a t t h e drag p o i n t t o the s u r f a c e f r e e energy i s g i v e n by 9  £b  q.  =  Vy  ' —  y  Thus, when q i s l e s s t h a n u n i t y , t h e s u r f a c e d r a g f o r c e exceeds the i n i t i a l f o r c e t o operate the s u r f a c e source and d i s l o c a t i o n s w i l l be pinned u n l e s s the s t r e s s is raised sufficiently.  F o r the case o f z i n c q = 2.25  greater than u n i t y .  the s u r f a c e i s c l e a n , mercury c o a t i n g reduces the s u r f a c e energy f u r t h e r .  When  - 51  T h e r e f o r e , we  do not e x p e c t any  s u r f a c e d r a g e f f e c t from amalgamation of  -  zinc  monocrystals.  ( i i i ) Surface Anchoring E f f e c t Dislocations  t h a t i n t e r s e c t the s u r f a c e can be anchored as  a  consequence of s e l e c t i v e l a t t i c e d i f f u s i o n o f s u r f a c e a c t i v e atom a l o n g d i s l o c a t i o n pipe.  There i s the a d d i t i o n a l p o s s i b i l i t y t h a t  l o c a t e d n e a r t o but not  i n t e r s e c t i n g the  s u r f a c e may  c a l l e d "surface anchoring e f f e c t " . atomic s i z e of z i n c and  dislocations  a l s o be p i n n e d  s e l e c t i v e s o l u t e atmosphere or p r e c i p i t a t e f o r m a t i o n .  s u b s t i t u t i o n a l type of s o l u t i o n , p o s s i b l e  and  i n t e r a c t i o n between d i s l o c a t i o n  has  p o i n t e d out t h a t p a r t i a l d i s l o c a t i o n s w i t h a s t a c k i n g  can  interact with impurity  the  H.  s t a c k i n g f a u l t show f . c . c . Hex.)  instead  Suzuki  f a u l t i n between  atoms w i t h a c h e m i c a l form o f i n t e r a c t i o n .  f a u l t l a y e r s are C P .  The  n a t u r e and  may  stacking  f a u l t and  contribute  "outside".  The  of h e x a g o n a l .  difference  t o an e f f e c t i v e energy o f b i n d i n g  few  structure Therefore  s o l i d s o l u b i l i t y o f i m p u r i t i e s c o n t a i n e d i n the m a t r i x can v e r y w e l l  " w i t h i n " the  and  Hg = I.57S), w h i c h f a v o u r s  d i f f u s e d mercury w i l l be S u z u k i t y p e r a t h e r t h a n C o t t r e l l t y p e .  atomic l a y e r s w h i c h c o n s t i t u t e the  be  of zinc  and  (in f.c.c. stacking  by  This effect w i l l  Considering c r y s t a l structure  mercury (Zn: I.38A  the  differ  i s a thermochemical o f the  impurity  atoms t o the extended d i s l o c a t i o n .  Once an extended d i s l o c a t i o n a q u i r e s i t s  e q u i l i b r i u m amount of s o l u t e i t may  be d i f f i c u l t t o move compared t o the  free  dislocation.  I n view o f f o r e g o i n g argument, s u r f a c e a n c h o r i n g e f f e c t  originated  from s e l e c t i v e l a t t i c e d i f f u s i o n o f mercury atom a l o n g the d i s l o c a t i o n p i p e o r S u z u k i type l o c k i n g o f d i s l o c a t i o n s s u r p a s s e s the  o t h e r two  e f f e c t s showing an  - 52 -  e f f e c t on i n c r e a s e d c r i t i c a l r e s o l v e d shear s t r e s s .  Long exposure time a f t e r  mercury c o a t i n g and s h o r t t i m e h o l d i n g o f c o a t e d c r y s t a l s a t e l e v a t e d temperatures c o n f i r m the a n c h o r i n g e f f e c t o f d i f f u s e d mercury atoms i n c r e a s i n g the  c r i t i c a l r e s o l v e d shear s t r e s s .  C.  THE EFFECT OF MERCURY COATING ON THE WORK HARDENING OF ZINC SINGLE CRYSTAL The mercury c o a t i n g on the s u r f a c e o f z i n c s i n g l e c r y s t a l has brought  remarkable changes i n t h e d e f o r m a t i o n c h a r a c t e r i s t i c s such t h a t c r y s t a l s were e m b r i t t l e d w i t h the f o l l o w i n g observed r e s u l t s . (1)  I n c r e a s e d work h a r d e n i n g s l o p e i n s t a g e A.  (2)  Decreased t r a n s i t i o n s t r a i n ,  (5)  I n c r e a s e d work h a r d e n i n g s l o p e i n stage B.  (4)  Decreased f r a c t u r e s t r e s s and  from s t a g e A t o stage B.  strain.  In t h e d e f o r m a t i o n o f z i n c s i n g l e c r y s t a l s , r e c o v e r y p r o c e s s e s are o p e r a t i v e above ~30°0.  Mott  2 5  has proposed t h a t s t a t i c r e c o v e r y i s due t o the  c l i m b motion of edge d i s l o c a t i o n s and suggested t h a t dynamic r e c o v e r y a l s o c o u l d be based on the same atomic p r o c e s s . of  Seeger and T r a u b l e  2 6  observed the f a n n i n g  s l i p l i n e s , shown s c h e m a t i c a l l y i n F i g . JO,which does not appear a t l o w e r  temperature and came t o t h e c o n c l u s i o n t h a t the t h e r m a l l y a c t i v a t e d r e c o v e r y p r o c e s s i n z i n c i s due t o the c l i m b motion o f edge d i s l o c a t i o n s .  This idea  makes an a t t r a c t i v e c o n t r a s t i n r e l a t i o n s h i p t o t h e case o f f a c e c e n t e r e d cubic metals i n w h i c h c r o s s s l i p by screw d i s l o c a t i o n s p l a y s an analogous r o l e f o r dynamic r e c o v e r y .  -  -LX  Fig.  30-  53  .-tea  Schematic P i c t u r e o f Fanning P r o c e s s a t b o t h ends of t h e same s l i p l i n e .  H i rath, e t a l  have shown t h a t h i g h l y m o b i l e v a c a n c i e s condense  t o form a d i s l o c a t i o n r i n g .  A c c o r d i n g t o t h e i r argument, t h e a n i s o t r o p i c  nature of the hexagonal c r y s t a l s t r u c t u r e f o r c e s these d i s l o c a t i o n r i n g s t o s t a y on the b a s a l p l a n e and t h e y a r e h i g h l y immobile because t h e i r v e c t o r i s p e r p e n d i c u l a r t o the b a s a l plane.  Burger's  Consequently, t h i s k i n d of  vacancy o r vacancy group c o n d e n s a t i o n w h i c h o c c u r s i n s t a t i c o r dynamic r e c o v e r y p r o c e s s enables us t o e x p l a i n t h e observed work h a r d e n i n g c h a r a c t e r i s t i c s of hexagonal m e t a l s .  D i s l o c a t i o n r i n g s w i t h diameter  less  t h a n lOoS have no s u b s t a n t i a l e l a s t i c s t r e s s f i e l d because o f t h e i r d i p o l e characteristics . 2 6  However, t h e s e d i s l o c a t i o n r i n g s can a c t as s h o r t range  o b s t a c l e s r e s t r a i n i n g the motion o f g l i d e d i s l o c a t i o n s .  The number of v a c a n c i e  i s p r o p o r t i o n a l t o t h e degree o f d e f o r m a t i o n and as a consequence, t h e number of d i s l o c a t i o n r i n g s a l s o i n c r e a s e s w i t h s t r a i n . compensating  The unbalance  of counter  p r o c e s s e s , namely, t h e f o r m a t i o n o f d i s l o c a t i o n r i n g s and  their  e l i m i n a t i o n t h r o u g h t h e c l i m b motion p r o v i d e the u n d e r s t a n d i n g o f work h a r d e n i n i n hexagonal m e t a l s .  Though t h e d i s l o c a t i o n r i n g s a r e e n e r g e t i c a l l y more  s t a b l e t h a n a t o m i c a l l y d i s p e r s e d v a c a n c i e s , t h e y a r e not u n d e r thermodynamic equibrium. process.  T h e r e f o r e t h e y can be annealed out by s t a t i c o r dynamic r e c o v e r y The t r a n s i t i o n from s t a g e A t o B i s a t t r i b u t e d t o a c r i t i c a l  c o n c e n t r a t i o n o f d i s l o c a t i o n r i n g s r e s u l t i n g from the unbalance o f the mentioned c o u n t e r compensating p r o c e s s e s .  The  changes o f work h a r d e n i n g  c h a r a c t e r i s t i c s of c o a t e d c r y s t a l s can be e x p l a i n e d by t h e between d i s l o c a t i o n r i n g s and  above  interaction  d i f f u s e d mercury atom.  M i c r o s c o p i c e x a m i n a t i o n t o d e t e c t the d i s t a n c e of d i f f u s i o n not  successful  due  f o r m a t i o n o f any d e f o r m a t i o n and process.  The  t o the  new  l a c k o f a d i s t i n c t boundary r e s u l t i n g from  phase o r compound.  the  D i f f u s i o n a l s o occurs during  i n c r e a s e d number o f s t r u c t u r a l d e f e c t s a c c e l e r a t e  the  was  the diffusion  i n c r e a s e d p e n e t r a t i o n o f mercury atoms r e s u l t i n g from l o n g  exposure t i m e o r h i g h e r temperature t r e a t m e n t s h o u l d cause more e m b r i t t l e m e n t , due  t o enhanced d i f f u s i o n o f mercury atoms and  hence an i n c r e a s e d  interaction  w i t h the d i s l o c a t i o n r i n g s .  T h e r e f o r e a r e d u c t i o n of dynamic r e c o v e r y r e s u l t s  from the  s h o r t range o b s t a c l e s ,  f o r m a t i o n of s t a b l e  causing s u b s t a n t i a l  changes  i n the work h a r d e n i n g c h a r a c t e r i s t i c s .  From the arguments d e v e l o p e d w i t h the o f h e x a g o n a l m e t a l s , we (1)  The  r e a c h the  following  a i d of deformation theory  summaries.  i n t e r a c t i o n between d i f f u s e d mercury atoms and  d i s l o c a t i o n rings  r e s p o n s i b l e f o r i n c r e a s e d work h a r d e n i n g s l o p e i n stage A and t r a n s i t i o n s t r a i n from stage A t o (2)  is  decreased  B.  I n c r e a s e d amount of p r e s t r a i n i n t r o d u c e s more d i s l o c a t i o n r i n g s w h i c h can  i n t e r a c t w i t h d i f f u s e d mercury atoms r e s u l t i n g i n e a r l y f a i l u r e  of  crystals. (3)  H i g h temperature t e s t s s u p p o r t the embrittlement.  r o l e of d i f f u s i o n i n l i q u i d metal  High temperatures a c c e l e r a t e  b o t h s u r f a c e and  lattice  d i f f u s i o n p r o m o t i n g the p o s s i b i l i t i e s o f i n t e r a c t i o n between d i f f u s e d  - 55  mercury atoms and d i s l o c a t i o n r i n g s . (k)  The i n c r e a s e o f work h a r d e n i n g  s l o p e i n stage B and d e c r e a s e d f r a c t u r e  s t r e s s and s t r a i n can be e x p l a i n e d b y analogous argument as a l r e a d y mentioned.  D.  PROPOSED MECHANISM FOR CRACK INITIATION I n non-coated c r y s t a l s t e s t e d i n t e n s i o n a t room  severe t w i n n i n g p r e c e d e d t h e f r a c t u r e .  Careful metallographic  r e v e a l e d t h a t c r a c k was p r o p a g a t e d a l o n g t h e b a s a l The  temperature, examination  plane i n twinned  r e l a t i o n s h i p between t h e shear and t h e u n d i s t o r t e d p l a n e w h i c h d e s c r i b e s  the t w i n n i n g i n z i n c can be i l l u s t r a t e d by F i g . 3 1 .  (OOOl)  >i K "*f  2  After twinning  In twin Twinning P l a n e (I0T_) (0001) In matrix  F i g . 31*  The  part.  K (1012)  In matrix  Geometry o f Twin i n Z i n c .  common form o f t w i n i n z i n c i s a compound t w i n i n Vwhich we have K  x  ^_  = (1012)  = (1012)  K  = [1011]  -Jjfe = [1011]  2  - 56 -  where K_ = the t w i n n i n g p l a n e o r the f i r s t u n d i s t o r t e d p l a n e , K u n d i s t o r t e d plane  7£ 1  =  shear d i r e c t i o n and 2  x  = the second  = the d i r e c t i o n d e f i n e d by  the i n t e r s e c t i o n o f the p l a n e o f shear w i t h K . plane which i s mutually p e r p e n d i c u l a r t o K  2  The p l a n e o f shear i s t h e  and K , and c o n t a i n s 2  and ^  2  .  A f t e r t w i n n i n g , the a n g l e between (0001) m a t r i x and (0001) t w i n  2S i s 94° and we can a p p l y Zeners  model f o r c r a c k i n i t i a t i o n .  I t i s conceivable  t h a t t w i n boundary performs the f u n c t i o n o f s t a b l e o b s t a c l e a g a i n s t the motion of d i s l o c a t i o n s and d i s l o c a t i o n s on a s l i p p l a n e emanated from a Frank-Read source encounter  a b a r r i e r ( t w i n boundary) where t h e y w i l l p i l e up e x e r t i n g  c o n s i d e r a b l e p r e s s u r e on the few o f them a t the head o f l i n e .  As t h e p r e s s u r e  b u i l d s up, t h e r e are two a l t e r n a t i v e s , (1) the o b s t a c l e w i l l be overcome and s l i p w i l l c o n t i n u e , (2) t h e l e a d i n g d i s l o c a t i o n s w i l l be f o r c e d t o g e t h e r t o form a c r a c k n u c l e u s .  Fig.  T h i s i d e a i s i l l u s t r a t e d d i a g r a m < a t i c a l l y i n F i g . 32.  32.  Zener's Model f o r the N u c l e a t i o n o f C r a c k by D i s l o c a t i o n C o a l e s c e n c e as an A l t e r n a t i v e to S l i p Propagation.  - 57  T h e r e f o r e , i f d i s l o c a t i o n s moving on t h e (0001) m a t r i x p i l e up a g a i n s t t w i n boundary, a wedge-shaped v o i d normal t o t h e (0001) m a t r i x and almost to  (0001) t w i n c a n be formed.  t h i s v o i d and propagated  parallel  T h i s i m p l i e s t h a t c r a c k c a n be n u c l e a t e d from  a l o n g (0001) t w i n (see F i g . 2k).  When t h e exposure time a f t e r mercury c o a t i n g was s h o r t (5-15 mins) the c r y s t a l s f a i l e d by Zener t y p e c r a c k i n i t i a t i o n . o c c u r r e d a t l e s s shear s t r a i n compared t o uncoated s h o r t e n i n g o f stage A.  Of c o u r s e , f r a c t u r e c r y s t a l s because o f t h e  When t h e time o f exposure i n a i r a f t e r mercury c o a t i n g  i n c r e a s e d beyond 15 mins., a c o m p l e t e l y d i f f e r e n t t y p e o f f r a c t u r e appeared. The  f r a c t u r e p l a n e was t h e b a s a l p l a n e o f m a t r i x c r y s t a l and specimens f a i l e d  i n stage A b e f o r e t w i n s o c c u r .  T h i s k i n d o f f r a c t u r e was a l s o observed i n  p r e s t r a i n e f f e c t and h i g h e r temperature  e f f e c t experiments.  d i s l o c a t i o n r i n g s formed b y t h e c o n d e n s a t i o n  The number o f  o f v a c a n c i e s and t h e n  by d i f f u s e d mercury atoms c o u l d be i n c r e a s e d under above mentioned conditions.  Therefore, i t i s understandable  stabilized experimental  t h a t these r i n g s a c t as s h o r t -  range o b s t a c l e s a g a i n s t t h e m o t i o n o f d i s l o c a t i o n s . 29  Gilman and Read  have i n v e s t i g a t e d t h e f o r m a t i o n o f t e n s i l e k i n k  w i t h v a r i o u s shapes o f z i n c m o n o c r y s t a l s .  They came t o t h e c o n c l u s i o n t h a t  b o t h a x i a l t w i s t i n g and c u r v a t u r e o f t h e s u r f a c e r e s u l t i n g f r o m t e n s i l e k i n k can occur i f t h e shear s t r a i n s due t o s l i p p i n g on a g i v e n b a s a l p l a n e a r e heterogeneous a c r o s s t h e b a s a l p l a n e .  They a l s o observed  that plated films  of copper a f f e c t e d t h e appearance o f t h e s u r r a t e d s u r f a c e s by i n c r e a s i n g t h e i r intensity.  T h i s suggests t h a t t h e e g r e s s o f d i s l o c a t i o n was d i s t u r b e d b y  p l a t e d copper f i l m s t h e r e b y i n t r o d u c i n g t e n s i l e k i n k s . d e f o r m a t i o n o f b o t h c o a t e d and uncoated  During the t e n s i l e  c r y s t a l s , serrated surfaces with a  - 58  s e r i e s of s m a l l t e n s i l e k i n k s were observed and more embryos o f t e n s i l e appeared i n coated and l o n g e r exposed specimens (see m e t a l l o g r a p h i c vations).  kink  obser-  I n t e r a c t i o n between d i f f u s e d mercury atoms and d i s l o c a t i o n s o r  d i s l o c a t i o n r i n g s induced h e t e r o g e n i e t y k i n k s on t h e s u r f a c e of c r y s t a l s .  i n s l i p process r e v e a l i n g t e n s i l e  Frequent f a i l u r e of mercury c o a t e d c r y s t a l s  a t the k i n k bands suggest t h a t k i n k boundary can a l s o be a s t a b l e o b s t a c l e a g a i n s t d i s l o c a t i o n m o t i o n (see F i g . 25).  B o t h i n c r e a s e d number o f  stabilized  d i s l o c a t i o n s r i n g s and k i n k b o u n d a r i e s p e r f o r m the f u n c t i o n o f s t a b l e o b s t a c l e f o r the p i l e up of d i s l o c a t i o n . I n t h i s c a s e , we  can a p p l y B u l l o u g h  R o z h a n s k i i model f o r c r a c k i n i t i a t i o n shown i n F i g .  - Gilman -  33-  er OBSTACLE  (  0001)  F i g . 33-  Schematic of B u l l o u g h - Gilman - R o z h a n s k i i Model f o r C r a c k I n i t i a t i o n i n Z i n c .  Under the a c t i o n of a t e n s i l e s t r e s s _>  , the l a t t i c e i n the v i c i n i t y o f a  b l o c k e d group of d i s l o c a t i o n s bend about an a x i s p a r a l l e l t o the b a s a l p l a n e and p e r p e n d i c u l a r t o B u r g e r ' s v e c t o r . c r a c k may  If  6"  i s s u f f i c i e n t l y large, a cleavage  be i n i t i a t e d a l o n g the b a s a l p l a n e (see F i g .  26-27).  - >9 l  V I . CONCLUSION  (1)  I n t e r a c t i o n between d i f f u s e d s u r f a c e a c t i v e l i q u i d m e t a l and o b s t a c l e s to s l i p i s a p r e r e q u i s i t e f o r embrittlement during t e n s i l e of z i n c s i n g l e c r y s t a l s o r i e n t e d f o r s i n g l e  (2)  deformation  slip.  The p o s s i b l e o r i g i n s o f s t a b l e o b s t a c l e s are c o n s i d e r e d t o be: (a) d i s l o c a t i o n r i n g s formed by vacancy c o n d e n s a t i o n and  stabilized  by d i f f u s e d mercury atoms. (b) t w i n b o u n d a r i e s o r t e n s i l e k i n k w a l l s r e s u l t i n g from  non-uniform  d e f o r m a t i o n a c r o s s s l i p p l a n e s due t o t h e r e s t r a i n i n g o f t h e of g l i d e d i s l o c a t i o n s by short-range o b s t a c l e s ( s t a b i l i z e d  motion  dislocation  rings). (3)  The m o d i f i c a t i o n s o f work h a r d e n i n g c h a r a c t e r i s t i c s o f z i n c s i n g l e  crystals  r e s u l t i n g from mercury c o a t i n g a r e summarized t o be: (a) i n c r e a s e i n c r i t i c a l r e s o l v e d s h e a r s t r e s s , and i n c r e a s e o f work h a r d e n i n g s l o p e i n s t a g e A and stage B.  (k)  (b)  decrease i n t r a n s i t i o n s t r a i n from stage A t o B.  (c)  decrease i n f r a c t u r e s t r e s s and f r a c t u r e  strain.  C r a c k s are i n i t i a t e d a t t e n s i l e k i n k w a l l s o r t w i n b o u n d a r i e s , (depend on e x p e r i m e n t a l c o n d i t i o n s ) .  R e l e v a n t mechanisms f o r i n i t i a t i o n  and  p r o p a g a t i o n o f c r a c k s a r e c o n s i d e r e d t o be: (a) Zener-'s model f o r c r a c k s i n i t i a t e d a t t w i n b o u n d a r i e s . (b) B u l l o u g h - Gilman - R o z h a n s k i i model f o r c r a c k s i n i t i a t e d a t k i n k walls.  APPENDIX  A  THERMODYNAMICS OF THE SPREADING OF LIQUIDS ON SOLID P H A S E 30  The f r e e energy o f a substance, a t c o n s t a n t t e m p e r a t u r e ,  pressure  and c o n c e n t r a t i o n i s d e f i n e d as  f r e e s u r f a c e energy p e r square c e n t i m e t e r  ' P.T.N  1  where F = t h e f r e e energy o f t h e substance u s u a l l y expressed  ~if i s  and A = i t s s u r f a c e a r e a .  i n e r g p e r square c e n t i m e t e r o r dynes p e r c e n t i m e t e r .  Firs  o f a l l , t h e c o n d i t i o n f o r s p r e a d i n g t o occur i s t h a t f o r t h e e n t i r e system  dF  < 0  2  I t i s assumed t h a t i n t h e course o f s p r e a d i n g o f s p r e a d i n g o f l i q u i d b on a s u r f a c e a, t h e f o l l o w i n g a r e a r e l a t i o n s a r e o b t a i n e d .  d  A b  =  d  A  ab = " ^ a  . .... 3  then  \v  Let  -( b VQ A J  ' p._  e designed as t h e f i n a l s p r e a d i n g c o e f f i c i e n t S°/  ' ,  a  then  sb/a'  =  r< a  - (*v+  .....  5  where P,T = c o n s t a n t and t h e s u r f a c e s s a t u r a t e d b y t h e m u t u a l components i s designated by the primes.  F o r t h e s p e c i f i c case a t hand, component b i s the  l i q u i d and a t h e s o l i d .  S /  = *s  L  s L  s L  /  S  =  S  4'  =  2T  *Y  S  We, t h e r e f o r e , r e d e f i n e t h e s p r e a d i n g c o e f f i c i e n t s  -  ( * L  -  (  "  ( 2TL  +  +  *LS')  ^itial  *LS)  semi-initial  3L'S)  F  I  N  A  L  6 ..... 7  •••••  8  As a p r i m a r y guide from t h e above d i s c u s s i o n , we d e r i v e t h a t a n e c e s s a r y condition f o r spreading i s  - 62 -  APPENDIX B  DISLOCATION PIPE D I F F U S I O N  25  The term p i p e d i f f u s i o n , w h i c h has f r e q u e n t l y been a p p l i e d t o d i f f u s i o n along  dislocation,  might w e l l have been c o i n e d t o r e p r e s e n t t h e  l i n e o f vacant s i t e s l y i n g under d i s l o c a t i o n l i n e .  The core o f t h e d i s l o c a t i o n  may be d e f i n e d as t h e l a s t l i n e o f f i l l e d s i t e s i n t h e i n s e r t e d p l a n e o f an edge d i s l o c a t i o n t o g e t h e r w i t h t h e l i n e o f vacant s i t e s i n t o w h i c h t h a t p l a n e would grow by n e g a t i v e c l i m b . i n F i g . 1.  This i s i l l u s t r a t e d f o r a simple cubic l a t t i c e  An i n t e r s t i t i a l i n t h e d i s l o c a t i o n  i n t h e row o f vacant, s i t e s i n t h e c o r e ;  c o r e may be d e f i n e d as an atom  a v a c a n c y , as a n empty s i t e i n t h e  l i n e o f atoms i n t h e core ( F i g . 2 ) .  INSERTED \  PLANE /DISLOCATION  LINE  DISLOCATION  F i g . 1. Pare Edge D i s l o c a t i o n i n Simple C u b i c L a t t i c e .  F i g . 2.  LINE  Illustrating "Interstitial and "Vacancy" i n Pure Edge Dislocation.  - 63 -  C o n s i d e r a p l a n e c o n s t r u c t e d p e r p e n d i c u l a r t o t h e d i s l o c a t i o n l i n e and not c o i n c i d e n t w i t h a r e s t p o s i t i o n o f an i n t e r s t i t i a l atom i n t h e d i s l o c a t i o n . The p r o b a b i l i t y o f an atom jumping f r o m l e f t t o r i g h t a c r o s s t h i s p l a n e can be w r i t t e n . J.i-2  =  a c j ^  1  Where J _ - i s t h e f l u x from l e f t t o r i g h t a c r o s s t h e p l a n e , p ^ , i s t h e jump 2  f r e q u e n c y o f an atom i n an i n t e r s t i t i a l p o s i t i o n , and a c _ i s t h e p r o b a b i l i t y t h a t t h e i n t e r s t i t i a l s i t e t o t h e l e f t o f t h e r e f e r e n c e p l a n e i s o c c u p i e d by a t r a c e r atom ( a = l a t t i c e p a r a m e t e r ) .  The p r o b a b i l i t y o f a jump i n t h e r e v e r s e  d i r e c t i o n a c r o s s t h e p l a n e i s t h e n g i v e n by  J2-1  TT  = a  ( i c  +  a  "|| )  ..... 2  Where t h e d i s t a n c e between r e s t p o s i t i o n o f i n t e r s t i t i a l atom i s assumed t o be a, and  i s the l o c a l  g r a d i e n t i n i n t e r s t i t i a l t r a c e r atoms.  I f the free  energy r e q u i r e d t o c r e a t e an i n t e r s t i t i a l atom i n t h e d i s l o c a t i o n core i s  /\ G-j,  t h e n t h e p r o b a b i l i t y o f a g i v e n s i t e i n t h e c o r e c o n t a i n i n g an i n t e r s t i t i a l atoms is ..... 3  p = exp (- AGi/RT)  The p r o b a b i l i t y t h a t any o c c u p i e d s i t e c o n t a i n s a t r a c e r atom i s s i m p l y t h e l o c a l c o n c e n t r a t i o n o f t r a c e r atom C .  The combined p r o b a b i l i t y o f an i n t e r s t i t i a l  0  c o n t a i n i n g an atom w h i c h i s a l s o a t r a c e r atom i s , t h e n , t h e p r o d u c t C_ = C  c  exp (-  /RT)  ..... k  site  - 64 -  The n e t t r a c e r f l u x c a n be obtained, f r o m e q u a t i o n s  ( 1 ) , (2) and (4) and i s  g i v e n by J  net = "  PT  & 2  e x p  <" ^  G i  /RT)  5  Comparison o f e q u a t i o n 5 w i t h F i c k s f i r s t l a w i n d i c a t e s t h a D = a  Further  2  f  exp(-  A G i  6  /RT)  J~^- i s s i m p l y t h e p r o d u c t o f t h e v i b r a t i o n f r e q u e n c y o f an i n t e r s t i t i a l  atom on t h e d i s l o c a t i o n c o r e , ^  and t h e p r o b a b i l i t y t h a t t h e atom w i l l a c q u i r e  s u f f i c i e n t energy t o c r o s s t h e b a r r i e r between n e i g h b o u r i n g s i t e s . b a r r i e r between n e i g h b o u r i n g s i t e s has h e i g h t Hr=  J>exp(- ^  G  I f the  A G m , t h e jump f r e q u e n c y becomes  > T )  ..... 7  and e q u a t i o n 6 may be w r i t t e n  D = a  2  y exp[ -( A G i + AGm)/RT]  ..... 8  I t i s assumed t h a t , as soon a s an i n t e r s t i t i a l atom i s c r e a t e d and s e p a r a t e d from i t s " p a r e n t " v a c a n c y by a s i n g l e atomic d i s t a n c e , i t no l o n g e r i n t e r a c t s with that  vacancy.  APPENDIX C T e n s i l e Test Results r (Kg/cm2)  Specimen No.  c  RESULTS OF TENSILE TEST (specimens w i t h p r o t e c t e d end)  6 (Kg/cm2/u.s.) r _ ( K g / c m 2 ) A  A  B  *A-B(*>  e_.(Kg/cm2/u.s.)  T  Experimental Condition  (Kg/cm ) 2  F  ZXS-X-1  44° 46°  1.71  10.3  19  150  62.5  101.0  413  Non-coated R.T. t e s t .  ZX3-C-3  46° 48°  1.69  11.2  20  l4o  63.0  102.7  394  Non-coated R.T. t e s t  ZXS-D-3  48 k9°  l.8l  10.0  -  -  -  16.2  81  ^30$ p r e s t r a i n e d , c o a t e d and 5 m i n . e x p o s u r e . R.T. test  ZXS-D-2  48° 49°  I.69  10.3  -  —  -  16.3  91  30$ p r e s t r a i n e d , c o a t e d and 5 m i n . e x p o s u r e . R.T.test  ZXI-P-2  46° 48  1.67  11.0  -  -  -  19.2  151  100$ p r e s t r a i n e d , c o a t e d and 5 m i n . e x p o s u r e . R.T.test  ZX3-L-2  47 ° 47°  1.78  13.0  -  —  —  26.2  153  105$ p r e s t r a i n e d , c o a t e d and 5 m i n . e x p o s u r e . R.T.test  ZXZ-F-4  46* 48°  1.63  10.3  18  125  -  40.8  184  162$ p r e s t r a i n e d , c o a t e d and 5 m i n . e x p o s u r e . P.T.test  ZXI-F-3  46 48°  1.65  10.0  18  i4o  -  37.7  191  165$ p r e s t r a i n e d , c o a t e d and 5 m i n . e x p o s u r e . R.T.test  ZXI-N-3  44  46°  2.00  13.3  17  110  io4.i  304  c o a t e d and 5 m i n . exposure. R.T.test  c  c  d  '8 sees i n 50ccHg  95  Appendix I I I ( c o n t ' d ) T e n s i l e T e s t R e s u l t s (specimens w i t h p r o t e c t e d end)  T c (Kg/cm ) 9 (Kg/cm /u.s.) ^ ( K g / c m ) 2  2  2  r_m  0 (Kg/cm /u.s.) ^ ( K g / c m ) r f (#) 2  Experimental Condition  2  Specimen No.  X  ZXS-F-3  48° 49°  1.99  17.2  21  95  75  100.0  267  ZXS-F-2  48° 49°  1.95  17.2  22  100  70  97.6  254  c o a t e d and 5 m i n . exposure. R.T.test  ZXI-N-2  44° 46°  2.03  12.0  16  100  95  97.0  267  c o a t e d and 10 min. exposure. R.T.test  ZXI-0-4  42° 45°  2.03  16.0  21  90  70  59.0  173  c o a t e d and 15 min. exposure. R . T . t e s t  ZXI-0-2  42°  2.06  17.1  22  80  65  61.6  179  c o a t e d and 15 m i n . exposure. R . T . t e s t  ZXI-M-3  42° 44°  2.07  12.6  -  -  -  13.2  62  c o a t e d and 30 m i n . exposure. R . T . t e s t  ZXI-M-2  42° 44°  2.12  14.3  -  -  -  14.5  72  c o a t e d and 30 m i n . exposure. R . T . t e s t  ZXI-L-k  44° 46°  2.12  13.6  -  -  -  8.7  73  c o a t e d and 60 m i n . exposure. R . T . t e s t  ZXI-0-3  42° 1+5°  2.11  9.7  -  -  -  6.1  38  c o a t e d and 60 min. exposure. R . T . t e s t .  ZXI-V-2  46° 4 °  2.09  12.0  13.4  86  coated, 5 min. e x p o s u r e , 5 min i n 50°C b a t h and quench t o R.T. R.T. t e s t  A  0  7  8 sees i n 50ccHg  A  B  B  A coated and 5 m i n . exposure. R . T . t e s t  , OA  ON  i  Appendix I I I ( c o n t ' d ) T e n s i l e T e s t R e s u l t s (specimens w i t h p r o t e c t e d end) Specimen No.  Xc 9vo T ( Kg/cm ) © (Kg/cm2/ .s.) ^ _ ( K g / c m 2 )  ZXI-V-3  46°  2.20  11.0  ZXI-W-3  47° 48°  2.30  15.7  ZXI-V-1  46° 47°  2.24  13.8  ZXI-Y-3  48° 49°  2.52  ZXI-Y-2  48° k9°  2.46  2  A  C  l  A  B  r . (^) © A  B  (Kg/cm /i.s.) ^ ( K g / c m 2 ) 2  B  —  —  —  —  —  r (*) f  Experimental Condition  13.2  90  coated, 5 min. e x p o s u r e , 5 min. i n 50°C b a t h and quench t o R.T. R.T. t e s t  7-5  30  coated, 5 min. exposure, 5 min. i n 75° b a t h and quench t o R.T. R.T. t e s t  9-3  44  coated, 5 min. exposure, 5 min. i n 75°C b a t h and quench t o R.T. R.T. t e s t  4.6  7  coated, 5 min. exposure, 5 min. i n 95° b a t h and quench t o R.T. R.T. t e s t  5-5  10  coated, 5 min. exposure, 5 min. i n 95° b a t h and quench t o R.T. R.T. t e s t  ft- ' 8 sees i n 50ccHg  1 ON.  -J  Appendix I I I ( c o n t ' d ) R e s u l t s o f T e n s i l e T e s t (specimens w i t h n o n - p r o t e c t e d ends)  r  (Kg/cm ) © (Kg/cm /u.s.) T _ ( K g / c m ) * A - B ( * ) 2  2  6 B (Kg/cm /u.s.)  Experimental Condition  Specimen No.  X  ZXS-K-2  49° 1+9°  1.76  10.5  19  135  85  ZX3-I-2  k6°  48°  1.71  10.5  -  -  -  ZXS-T-3  46° 48°  1.73  15.3  -  135  -  150$ p r e s t r a i n e d , c o a t e d and 5 m i n . e x p o s u r e . R.T. t e s t  ZXS-T-2  k6°  48°  1.72  12.0  -  115  65  200$ p r e s t r a i n e d , c o a t e d and 5 m i n . e x p o s u r e . R.T. t e s t  ZXS-W-3  kh°  k6°  1.76  10.0  16  125  86  2 sees i n 50ccHg and 5 m i n .  ZXS-H-2  1+7° k  ZNX-F-2  kT  0  K  2  c  A  A  B  2  non-coated. R.T. t e s t A  M  100$ p r e s t r a i n e d , c o a t e d and 5 m i n . e x p o s u r e . R.T. t e s t  exposure. R.T. t e s t 9  1-75  12.2  kQ°  1.82  12.0  ZXS-J-1  kk° 1+6°  1.77  10.0  ZX3-G-3  kQ° 50°  1.79  13.0  ZXII-E-1  47°  48°  1.81  ZX3-W-2  kk"  k6°  I.83  23  125  70  20  115  50  2 sees i n 50ccHg and 5 min.  exposure. R.T. t e s t  2 sees i n 50ccHg and 5 m i n .  e x p o s u r e . R.T. t e s t  115  75  k sees i n 50ccHg and 5 m i n .  20  125  80  k sees i n 5 0 H g and 5 m i n . e x p o s u r e . R.T. t e s t  8.5  13  125  60  k sees i n 50ccHg and 5 m i n .  11. k  16  110  -  16  exposure. R.T. t e s t cc  e x p o s u r e . R.T. t e s t  6 sees i n 50ccHg and 5 m i n . exposure. R.T. t e s t  A  k sees i n 50ccHg ON CO  Appendix I I I ( c o n t ' d ) R e s u l t s o f T e n s i l e T e s t (specimens w i t h n o n - p r o t e c t e d ends) Specimen No. ZXS-G-1  Xo %o 48°  T  (Kg/cm ; 9 (Kg/cm /u.s.) 0T _ (Kg/cm ) 2  2  c  A  50°  1.84  2  A  11.8  B  9 (Kg/cm /u.s.) 2  *A-B<*>  B  Experimental Condition  19.  115  -  6 sees i n 50ccHg and 5 min. exposure. R.T. t e s t  ZXII-E-2  1+7°  48°  1.82  11.0  17  125  85  6 sees i n 50ccHg and 5 min. exposure. R.T. t e s t  ZXS-U-1  ky  45°  1.96  12.3  15  100  -  8 sees i n 50ccHg and 5 min. e x p o s u r e . R.T. t e s t  ZXS-D-1  48°  49°  2.02  12.0  -  -  -  8 sees i n 50ccHg and 5 min. e x p o s u r e . R.T. t e s t  ZXII-B-2  46° 46°  2.03  8 sees i n 50ccHg and 5 min. exposure. R.T. t e s t  I  VO  - 70 -  APPENDIX D  ESTIMATION OF ERRORS C r i t i c a l r e s o l v e d shear s t r e s s i s o b t a i n e d  r  t = —  from t h e r e l a t i o n  sin X cosXo  c  0  where P i s l o a d , A i s i n i t i a l c r o s s s e c t i o n a l a r e a and X o same meaning a s d e f i n e d p r e v i o u s l y . d i f f e r e n t i a t i n g e q u a t i o n (1),  an(  3 . ^ o have t h e  By t a k i n g n a t u r a l l o g a r i t h m s and  the t o t a l error involved i n c a l c u l a t i n g c r i t i c a l  r e s o l v e d shear s t r e s s i s  S% %  ^P  JA  +  +  (T(sinX ) 0  A  ' P  sinX  Jfcos9\ ) 0  +  cos9vo  0  The p o s s i b l e u n c e r t a i n t i e s a r e : (1)  t h e l o a d v a l u e from t h e c h a r t , t h e d e v i a t i o n p o i n t from l i n e a r i t y would be d e t e r m i n e d t o w i t h i n a t l e a s t 0.2 d i v i s i o n i n k, hence  = 2 ^  h. p  (2)  =  0 > 0 5  V  specimen c r o s s s e c t i o n , t h e micrometer c o u l d be r e a d t o 0.001cm i n 0.05 cm, hence  JA  =  A (3)  2(0.001) 0.05  =  Q k  t h e c r y s t a l o r i e n t a t i o n c o u l d be d e t e r m i n e d w i t h i n ±1° u s i n g t h e W u l f f n e t , hence f o r X  D  = 46° <f(sinXc) sinX 0  =  0.012 0.719  =  Q  Q  ±  7  - 71 -  and f o r  *\  0  = 46 0.012 0.695  COS  =  0.017  T h e r e f o r e , t o t a l u n c e r t a i n t i e s i n v o l v e d i n c r i t i c a l r e s o l v e d shear s t r e s s i s  7=r-  =  0.074  or  7.4$  The f l o w s t r e s s v a l u e s i n v o l v e a d d i t i o n a l parameter, t h e gage l e n g t h , v a r i a t i o n i n c r o s s s e c t i o n a l a r e a a l o n g gage s e c t i o n and t h e amount o f mercury c o a t e d . E s p e c i a l l y , t h e amount o f mercury c o a t e d on t h e s u r f a c e o f c r y s t a l s depends on the s u r f a c e c o n d i t i o n (degree o f micro  r e l i e f and p o s s i b l e c o n t a m i n a t i o n s ) and  t h i s w i l l a f f e c t t h e parameters d e f i n e d f o r comparison b u t t h e r e i s no r e l e v a n t way t o e s t i m a t e t h e r e s u l t i n g  error.  - 72 -  REFERENCES  1.  N i c h o l s , H., and R o s t o k e r , W., A c t a Met. 9, 504 (1961).  2.  Goryunov, U.V., P e r t s o v , N.V., and R e h b i n d e r , P.A., S o v i e t P h y s i c s "Doklady", 4, 840 ( i 9 6 0 ) .  3.  Heyn, E., J . I n s t . M e t a l s 12, 3 (1914).  4.  Rawdon, H.S., P r o c ASTM 18, 2, 189 (I918).  5.  Moor, R., and B e c k i n s a l e , S., J . I n s t . M e t a l s , 23, 225 (1920).  6.  M i l l e r , H.J., J . I n s t . M e t a l s , 37, 183 (1927).  7.  Rosenberg, R., and C a d o f f , I . , F r a c t u r e o f S o l i d s , E d i t e d by D.C. and J . J . Gilman (I962).  8.  Likhtman, V . I . , and Shchukm, E.D., S o v i e t P h y s i c s " U s p e k h i " , I.91 (I958).  9.  Shchikin, E.D., P e r s t o v , N.V., and Goryunov, U.V., S o v i e t P h y s i c s ( C r y s t a l l o g r a p h y ) , 4, 800 (1959).  10.  L a b z i n , V.A. and L i k h t m a n , V . I . , "Doklady", Akad Nauk, SSSR 121, 778 (I958).  11.  R e h b i n d e r , P.A., L i k h t m a n , V . I . , and Kochanova, L.A., "Doklady", Akad Nauk, SSSR 111, 1276 (1956).  12.  L i k h t m a n , V . I . , Kochanova, L.A., and Bryukhanova, L.S., "Doklady" Akad Nauk, SSSR 120, 757 (1958).  13.  Kamdar, M.H., and Westwood, A.R.C., E m b r i t t l e m e n t o f Z i n c M o n o c r y s t a l s and B i c r y s t a l s by Mercury and G a l l i u m , RIAS, March (I965).  14.  Kamdar, M.H ., and Westwood, A.R.C., C o n c e r n i n g L i q u i d M e t a l E m b r i t t l e m e n t P a r t i c u l a r l y o f Z i n c M o n o c r y s t a l s by M e r c u r y , RIAS, Dec. (I962).  15.  P e r s t o v , N.V., and R e h b i n d e r , P.A., "Doklady", Akad Nauk, SSSR, 124, 307,  Drucker  (1959). 16.  Anderson, E.A., M e t a l s Handbook, (1948).  17.  Simson, C.Von., Z. P h y s i k Chem. 109, 192 (1924).  18.  Boas, W., An I n t r o d u c t i o n t o t h e P h y s i c s o f M e t a l s and A l l o y s , 67, (1947).  19.  J i l l s o n , D.C,  T r a n s . AIME, 188 (1950).  - 73 -  References (cont'd) 20.  H a r k i n s , W.D., (1952).  P h y s i c a l C h e m i s t r y o f S u r f a c e , R e i n h o l d Pub. Co., N.Y.  21.  F r i c k e , R., Z. E l e k t r o c h e m . , 52, 72 (1948).  22.  P l e t e n e v a , N.A., and Fedoseeva, N.P., "Doklady", Akad Nauk, SSSR 151, 2 (1963).  23.  Love, G.R., A c t a Met. 12, 6 (1964).  24.  Frank, F.C., M a t h e m a t i c a l Theory o f S t a t i o n a r y D i s l o c a t i o n , P h i L Mag. Suppl., July(1952).  25.  M o t t , N.F., P h i l . Mag. 43 (1952), P h i l . Mag. 44 (1953).  26.  Seeger, A. Von., and T r a b l e , H., Z. Metalkunde  27.  H i r s c h , P.B., S i l c o x , J . , Smallman, R.E., and Westmacott, K.H., P h i l . Mag.  (i960).  3 897/(1958). 28.  Zener, C ,  " F r a c t u r i n g o f M e t a l s " , pp.3-31 ASM (1948).  29.  Gilman, J . J . , Read, T.A., T r a n s . AIME 194, 875 (1952).  30.  B o n d i , A., Chem. Rev., 52, 427 (1953).  

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