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The effect of small additions of titanium on the incubation period of isothermally transformed zirconium-niobium… Vanderpuye, Nee Attoh 1958

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THE EFFECT OF SMALL ADDITIONS OF TITANIUM ON THE INCUBATION PERIOD OF ISOTHERMALLY TRANSFORMED ZIRCONIUM-NIOBIUM ALLOY by NEE ATTOH VANDERPUYE  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n the Department of MINING AND METALLURGY  We accept t h i s thesis as conforming to the standard required from candidates f o r the degree of MASTER OF APPLIED SCIENCE  Members of the Department Mining and Metallurgy  THE UNIVERSITY OF BRITISH COLUMBIA September, 1958.  ABSTRACT  The general e f f e c t of small additions of titanium on the incubation period preceding the B —• a + 8 reaction i n an isothermally transformed zirconium - 17.6$ niobium a l l o y has been studied by observing e l e c t r i c a l resistance at constant temperature, by making micro-hardness t e s t s , by examining specimens metallographically and by employing X-ray d i f f r a c t i o n methods. I t was found that the e f f e c t of increasing the amount of titanium was t o lengthen the incubation period.  According to the e l e c t r i c a l resistance  data, an a l l o y containing 5$ titanium shows  an incubation period of approx-  imately 15 minutes while one containing 1555 titanium shows a period of approximately 25 minutes at 600°C.  Micro-hardness tests show the same  general e f f e c t ; however, corresponding incubation periods f o r the same alloys are  approximately 30 minutes and 40 minutes.  Although metallographic and  X-ray d i f f r a c t i o n results did not c o n f l i c t with these conclusions, i t has been pointed out that more data and some refinement i n technique are needed i n order that these might be employed to support resistance data with confidence. The presence of a hydride phase i n quenched and p a r t i a l l y transformed specimens was noted. unknown.  The effect of this phase on the mode and rate of reaction i s Clearly, further investigation i s necessary i f i t s effect on the  transformation must be  determined.  It has, however, been shown that the method of'observing transformations i n t h i s system with e l e c t r i c a l resistance i s both e f f e c t i v e and sound.  In presenting the  this  r e q u i r e m e n t s f o r an  thesis in partial  advanced degree at the  of B r i t i s h Columbia, I agree that it  freely  agree t h a t for  available  the  f o r r e f e r e n c e and  permission for extensive  s c h o l a r l y p u r p o s e s may  D e p a r t m e n t o r by  fulfilment  be  s h a l l make  study.  I  the  gain  s h a l l not  Department The U n i v e r s i t y o f B r i t i s h V a n c o u v e r S, C a n a d a . Date  Columbia,  Head o f  thesis my  I t i s understood  copying or p u b l i c a t i o n of t h i s t h e s i s a l l o w e d w i t h o u t my  further  copying of t h i s  that  be  University  Library  g r a n t e d by  his representative.  of  for  written  financial  permission.  ii  ACKNOWLEDGEMENT  The author i s g r a t e f u l f o r f i n a n c i a l aid i n the form of a research assistantship provided by the Defence Research Board of Canada under Research Grant DRB 7510-18. The author would l i k e to thank Dr. Barrie of the Physics Department most humbly f o r his help i n the analyses work and f o r showing u n t i r i n g interest i n the investigation generally. Many thanks  to  Mr. R. Butters and Mr. R. Richter f o r the  invaluable t e c h n i c a l advice and assistance they rendered.  F i n a l l y , the  author i s most indebted to Dr. V. G r i f f i t h s under whose d i r e c t i o n t h i s i n v e s t i g a t i o n was performed.  iv TABLE OF CONTENTS  CHAPTER I.  PAGE INTRODUCTION Purpose  .  . . . . . . . .  1  . . . . . . .  1  The I n c u b a t i o n P e r i o d and I s o t h e r m a l T r a n s f o r m a t i o n  . . . .  The Z i r c o n i u m - N i o b i u m System  6  Composition o f Ternary I n v e s t i g a t e d  . . . . . . . . . . . .  E f f e c t of Impurities  EXPERIMENTAL Alloy Preparation  2.  R e s i s t a n c e Measurements  4.  III.  13  15 .  18  Apparatus  18  Procedure  23  R e s u l t s and D i s c u s s i o n  23  M i c r o - h a r d n e s s Measurements  31  Procedure  31  R e s u l t s and D i s c u s s i o n  34  Met a l i o g r a p h i c  39  R e s u l t s and D i s c u s s i o n 5.  .  15  1.  3.  9 9  Techniques f o r S t u d y i n g T r a n s f o r m a t i o n s  II.  2  X-Ray D i f f r a c t i o n  . .  39 42  Procedure  42  R e s u l t s and D i s c u s s i o n  42  CONCLUSIONS  44  Table of Contents (Cont'd.) CHAPTER IV.  PACE APPENDICES A.  C o n s t i t i t i o n a l Diagrams  . . . . . . . . . .  Ti-Nb B. „ Constitutional  V.  CI*  AllcllySXS  CII.  Analysis  2  . . . . . . . . . . . . . . .  48  . . . . . . . . . . . . . . . . .  U&  2jJ?""]vJjp  6  2F~H2  o  Q  e  o  «  •  «  «  •  t  •  •  >  >  »  •  t  >  )  '  »  O  O  O  O  o  o  o  O  o  O  O  o  0  o  O  o  A" ^  o  5^ 51  ftoeoAoeoooAtoootjvoooooo  53  D«  RSSXS"bcinC©  E.  Hardness Data  F.  X=Ray D i f f r a c t i o n Data  BIBLIOGRAPHY  47  Diagrams Zr-0  46  DcL"beL e o « e a « o * « e o « *  . . . . .  . . . . . • • « . .  o  o  o  o  o  o  o  . . . . . .  5^ 60 62  . . . . . . . . . . . . . .  53  vi LIST OF ILLUSTRATIONS FIGURE  PAGE  1.  T-T-T c h a r t f o r zirconium-7% n i o b i u m a l l o y ( a f t e r Domagala) . .  3  2.  T e n t a t i v e T-T-T c h a r t f o r z i r c o n i u m - 1 6 . 4 $ (after Finlayson)  3  3. 4.  niobrium a l l o y  T-T-T c h a r t f o r z i r c o n i u m - 5 . 4 $ molybdenum a l l o y ( a f t e r Domagala and coworkers) .  4  T-T-T c h a r t f o r zirconium-7.5/& molybdenum a l l o y ( a f t e r Domagala and coworkers)  4  5.  The z i r c o n i u m - n i o b i u m phase diagram ( a f t e r Rogers and A t k i n s ) , . ~  6.  Isothermal s e c t i o n of zirconium-niobium-titanium ternary at 800°C ( a f t e r Whitmore) Isothermal section o f zirconium-niobium-titanium ternary at 700°C ( a f t e r Whitmore)  10  Isothermal section of zirconium-niobium-titanium ternary at 650°C ( a f t e r Whitmore)  11  Isothermal s e c t i o n o f zirconium-niobium-titanium t e r n a r y at 600°C ( a f t e r Whitmore)  11  Isothermal section o f zirconium-niobium-titanium ternary at 550°C ( a f t e r Whitmore)  12  7. 8. 9. 10. 11.  8  10  M i c r o s t r u c t u r e o f quenched zirconium-niobium-5% t i t a n i u m alloy  12  12.  Diagram of l e v i t a t i o n m e l t i n g apparatus  17  13.  T y p i c a l i n g o t produced b y l e v i t a t i o n m e l t i n g  18  14.  . Diagram o f r e s i s t a n c e measuring c i r c u i t  19  15.  G e n e r a l v i e w o f apparatus  21  16.  Vacuum f u r n a c e assembly  21  17.  Diagram o f f u r n a c e and vacuum chamber assembly  18.  P l o t o f r e s i s t a n c e vs temperature  . . . . . . . .  d u r i n g slow heat o f 5%  22 24  titanium alley 19.  P l o t o f r e s i s t a n c e v s t i m e f o r 5$ t i t a n i u m a l l o y  20.  P l o t o f r e s i s t a n c e v s time f o r 15% t i t a n i u m a l l o y  25,26 . . . . . .  27,28  FIGURE 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31.  PAGE Relative positions of incubation periods f o r 5% and 15% titanium alloys  29  Plots of resistance vs temperature f o r bcc and c.p. hex. structures of 5% titanium a l l o y  32  Plots of resistance vs temperature f o r bcc and c.p. hex. structures of 15% titanium a l l o y  33  Plots of Diamond Pyramid Hardness vs time f o r various heattreatments of 5% titanium a l l o y  35,36  Plots of Diamond Pyramid Hardness vs time f o r various heattreatments of 15% titanium a l l o y  37,38  Microstructure of 5% titanium a l l o y held at 400° C f o r 30 minutes . . . . .  40  Microstructure of 5%' titanium a l l o y held at 400°C f o r 30 minutes  40  Microstructure of 5% titanium a l l o y held at 500°C f o r 4 hours  40  Microstructure of 5% titanium a l l o y held at 500°C f o r 8 hours  40  Microstructure of 5% titanium a l l o y held at 600°C f o r 1 week  41  Microstructure of wire specimen transformed at 600° f o r 5 hours  41  viii  LIST OF TABLES  TABLE  PAGE  1.  Analysis of c r y s t a l bar zirconium  2.  Typical analysis o f c r y s t a l bar titanium  3.  S p e c t r o g r a p h i c a n a l y s i s of n i o b i u m r o d  15 .  15 16  THE EFFECT OF SMALL ADDITIONS OF TITANIUM ON THE INCUBATION PERIOD OF ISOTHERMALLY TRANSFORMED ZIRCONIUM-NIOBIUM ALLOY :  I.  INTRODUCTION  Purpose Comprehensive experimental programmes undertaken to develop zirconium aim at f u l f i l l i n g two objectives? and knowledge of the m e t a l l i c state;  f i r s t l y , to enlarge the theory  secondly and perhaps of more immediate  import i s the development of suitable alloys f o r i n d u s t r i a l use.  I t i s the  purpose of t h i s investigation to add to the general data on zirconium by studying the effect of small additions of titanium on the incubation period of an isothermally transformed  zirconium-rich niobium a l l o y .  i t complements an isothermal transformation study of a  Specifically,  zirconium-niobium  a l l o y conducted by Finlayson''" and work on the c o n s t i t u t i o n a l diagram of a  2 zirconium-niobium-titanium  ternary recently completed by Whitmore.  The nature and h i s t o r y o f the studies on zirconium and zirconium alloys have been dealt with by Lustman^ and Kerze.  Recently a c r i t i c a l  review of the a l l o y i n g behaviour of the metal has been published by P f e i l . ^ P f e i l has also treated the t h e o r e t i c a l aspects of the a l l o y i n g behaviour of zirconium i n another report.''  The most extensive application of zirconium i n  industry i s i n certain types of nuclear reactors where the low absorption cross section f o r thermal neutrons i s the chief c i t e d property of the. metal. Niobium, l i k e zirconium, has useful properties applicable to reactor design. Lately, interest i n ternary alloys has grown owing to t h e i r success i n meeting certain operating requirements  i n some nuclear reactors.  - 2 The Incubation Period and Isothermal  Transformation  Zirconium exhibits a l l o t r o p y .  The low temperature modification, a  close packed hexagonal structure, i s stable below 862°C.  Above t h i s tempera-  ture and up to the melting point, 1860°C, the stable phase, beta, possesses a body-centered cubic sturcture.  It has been established-^ that i f pure zirconium  i s homogenized above the t r a n s i t i o n temperature and then quenched, i t i s impossible t o retain the beta phase.  However, the addition of a second element  makes retention of the beta phase possible but i n varying degrees depending upon the element and the amount present. the sluggishness  The degree of retention i s shown by  of the forward reaction (B —• a + B).  The length of the  incubation period which precedes the reaction i s a measure of the of the reaction.  The isothermal studies of Domagala^ on Zr-Nb a l l o y s , of  7  Domagala' and coworkers on Zr-Mo a l l o y s , and f i n a l l y of Finlayson a l l o y a l l show incubation periods preceding the start of Figures 1, 2,  sluggishness  1  on Z r - l 6 % Nb  transformation.  3, and 4 show the isothermal diagrams (or Time Temperature Trans-  formation charts) of Domagala, Finalyson, Domagala and coworkers. diagrams are based upon e l e c t r i c a l resistance data.  Of the two  These  zirconium-  niobium a l l o y s investigated by Domagala, only one chart representing the niobium a l l o y i s shown here.  7%  However, a quick study of e l e c t r i c a l resistance  data f o r the 15% niobium a l l o y c l e a r l y reveals the e f f e c t of additions of niobium upon the incubation period. i s greater than that f o r 7% a l l o y .  The incubation period f o r the 15% a l l o y The two  charts^ of the zirconium-molybdenum  system, (Figures 3 and 4) together with two others not reproduced here, also show that increasing amounts of molybdenum lengthen the incubation period.  At  600°C, the incubation periods preceding the S —• a + B reaction are half a minute and two minutes f o r 5.4% and 7.5% Mo alloys respectively.  The transformation requires that a nucleus of the new phase must form  - 3 -  900.  Specimens isothermally quenched from 1000°C.  800o o  f-l 700CD  a  cUd  -P  600-  + B  CO EH  50C'  /3 * uf n  m i l  10 Figure 1.  i  i iiIm)  i  100 Time - minutes  i i i u r ni  i1  i  i i 111 it  1000  10000  T-T-T chart f o r a Zv-7% Wo a l l o y (after Domagala ) 5  800 — 700 o u  600  0 -p  ed U <D  500  E-t  400  &  o Figure 2.  oo Q  10  Time  o  a + 3  O  100 minutes  1000  Tentative T-T-T chart f o r Zr-l6,4?5 Nb a l l o y (after F i n l a y s o n ) . 1  10000  - 4 -  Specimens 'isothermally quenched from 1000°C,  • *«• i*•  Figure'3.  i 1 1 1 1 i n i — i n ) nii..—> 1111 IIiiiijij. i _i i 10 100 1000 Time - minutes  i ijijj.ii 10000  T-T-T chart f o r Zr-5.4% Mo a l l o y (after Domagala and coworkers?).  900 -  o o  800 -  700 -  600  1  3  500f-  400  Mr  1  10 100 Time - minutes  1000  10000  Figure 4. T-T-T char-t f o r Zr-7.5% Mo a l l o y (after Domagala and coworkers')  - 5• and reach a c r i t i c a l size before the growth of the nucleus can be assured. Apparently the incubation period i s the time i t takes to nucleate the transformation.  The whole process of nucleation and subsequent transformation i s  controlled by composition fluctuations and d i f f u s i o n of the atoms involved. It i s generally believed that the rate of d i f f u s i o n of atoms during such transformations i s decreased by impurities.  Thus i t can be understood why  a l l o y additions generally have the effect of increasing the incubation period. At high temperatures the v i b r a t i o n a l frequency of atoms i s high and consequentl y the p r o b a b i l i t y of destruction of nuclei of the new phase i s equal to that of formation.  At low temperatures,  the rate of d i f f u s i o n i s much lower; hence  the p r o b a b i l i t y of formation of these n u c l e i i s also small.  I t may be assumed,  therefore, that some intermediate temperature range offers the optimum opportunity f o r the formation and subsequent growth of nuclei of the new phase. If the p r o b a b i l i t y f o r the reaction taking place bears any r e l a t i o n to the incubation time, then the general nature of the incubation time versus temperature curve should be a C* with at least one minimum i n the time ordinate at f  some intermediate temperature.  Thus the length of the incubation period i s a  function of temperature as w e l l as the type and amount of impurity present.  The transformation represents an i r r e v e r s i b l e reaction i n which the stable product i s f i r s t nucleated and then grown at the expense of the reactant. phase.  In c o n s t i t u t i o n a l studies, equilibrium conditions are maintained.  However, subcooling, such as practised i n t h i s investigation, represents marked departure from equilibrium cooling. products as well as stable ones.  The reaction thus may produce intermediate  Figures 1, 3, and 4 show an'w phase that i s  not evident i n the c o n s t i t u t i o n a l diagrams of zirconium-niobium molybdenum systems.  and zirconium-  A l i t e r a t u r e search revealed that several general analyses  have been made of the isothermal transformation i t s e l f  and not of the incubation  - 6period.  These show the nature of the time-dependence.  Austin and R i c k e t t set 0  the f r a c t i o n transformed as: a where K i and p are constants.  - K i (1 - a)tP  (1)  The rate of reaction was given by T. Mishima,  Hasiguti and Kimura^ as: da dt v  -  K ^  1  )  ( 1 - a)(P >/ + 1  P  (2)  An approach more generally used i s to take the right hand side of the equation (1) as the rate of transformation and: da dt  =  K (1 - a ) tm-1  (3)  Integration gives: a = 1-exp [_-K t J m  4  = 1-exp K = K 3/m  with where t  =  rf  (4) .-m  i s a time constant.  The Zirconium-Niobium System. Pfeil  5  and Smoluchowski  3  have discussed the t h e o r e t i c a l aspects of  the a l l o y i n g behaviour of zirconium, while Mcintosh"^ has reviewed the a l l o y systems of niobium.  Literature search revealed that actual experimental work  on the zirconium-niobium system was f i r s t performed by Anderson and coworkers at the U.S. Bureau of M i n e s .  11  Their results showed that i t i s indeed d i f f i c u l t  to r e t a i n beta i n pure zirconium, for'of the three alloys prepared, 0.6$*, 5.1$ and 12.9$> increasing amounts of beta were retained as the niobium content grew larger.  i  The alpha phase was described as Widmanstatten structure i n the 0 6%  A l l compositions, unless otherwise stated, are i n weight percent.  0  alloy.  The f a c t that the 12.9% a l l o y showed much larger grains indicated that  the beta —*• alpha transformation took place at a r e l a t i v e l y low temperature. C l e a r l y the transformation temperature i s depressed by a l l o y i n g with niobium. In general, simple s u b s t i t u t i o n a l a l l o y i n g w i l l produce a stronger m a t e r i a l by 1o v i r t u e of the induced l a t t i c e s t r a i n .  Simcoe  and Mudge observed an increase  i n strength i n both 0.5% and 1.0% niobium alloys made .with  hafnium-containing  13 zirconium.  According to Keeler,  the strength of zirconium i s increased by  additions of niobium to a content of at least 3%.  This general strengthening  effect i s borne out i n part by the r e s u l t s of Anderson^ and L i t t o n ^ which are reproduced  i n Finlayson's report.  If i t i s assumed that the beta structure i s  weaker than the alpha, then a second effect such as the sluggishness of the transformation caused by the addition of some element or by heat treatment  may,  by inducing large amounts of beta to be present, render the f i n a l m a t e r i a l to be weaker than would be expected from substitution alone.  Thus the difference  between the y i e l d strength values of L i t t o n and those of Anderson was  probably  due to inconsistent heat-treating. 15 In 1952 Hodge  investigated the zirconium system up to 25% niobium.  He suggested t e n t a t i v e l y that the eutectoid i n the zirconium-rich a l l o y s l a y at about 625°C and 10% niobium and estimated that the s o l u b i l i t y of niobium i n zirconium at 625°C was near  6%.  The c o n s t i t u t i o n a l diagram of- Rogers and Atkins- - published i n 1955 1  i s shown i n Figure 5. 6.5%.  0  S o l u b i l i t y i n alpha zirconium reaches a l i m i t at about  The system thus shows age-hardening e f f e c t s .  The iodide zirconium  employed by Rogers and Atkins contained traces of hafnium (less than 0.05%). The chief impurities i n the niobium were tantalum s i l i c o n and titanium.  (0.5%) and traces of i r o n ,  Figure 5  0  The zirconium-niobium phase diagram ( a f t e r Rogers and A t k i n s ) 17  In 1956, Domagala and McPherson the ~zirconium-niobium system.  reported t h e i r i n v e s t i g a t i o n of  Although they used iodide zirconium and h i g h a  p u r i t y ' niobium powder, they agreed w i t h Rogers and A t k i n s only i n p a r t  0  For  they put the eutectoid h o r i z o n t a l at 800°C, the eutectoid composition at 17% niobium and maintained that a continuous s e r i e s of s o l i d s o l u t i o n s e x i s t e d o n l y above 1180°C. 1$  Again, i n 1957, Bychkov  and coworkers presented a phase diagram  that was inconsistent w i t h that of Rogers and A t k i n s .  Their eutectoid  h o r i z o n t a l was at 550°C and the eutectoid composition at 12% niobium. Furthermore, the minimum i n the s o l i d u s was at 1600°C rather than at 1740°C as found by Rogers and A t k i n s .  - 9Composition o f Ternary  Investigated  The addition of titanium to a zirconium-niobium ternary.  In order t o appreciate the ternary diagram, the two other binariesj,  Z r - T i and Ti-Nb, are shown i n Appendix A. Fast  19 7  alloy results i n a  The diagram Z r - T i shown i s that of  with s l i g h t modifications by Hayes et a l .  20  That representing  Pi titanium-niobium was determined by Hansen  et a l . From Whitmore°s investiga-  t i o n of the zirconium-rich side of the zirconium-niobium-titanium f i v e isothermals are presented  i n Figures 6, 7, 8, 9 and 10,  thermals at 800°C, 700°C, 650°C, 600°C and 550°C,  ternary j,  These are i s o -  I f the proportion of  zirconium to niobium i s kept constant, then the addition of titanium may be 22 shown e a s i l y since i t w i l l l i e on a ternary i s o p l e t h .  The proportion of  zirconium to niobium i n the ternary a l l o y was 7:1,5 or 17,6% Nb i n a zirconiumniobium a l l o y .  Alloys containing 5% and 15% titanium (shown on the ternary  isopleth i n Figures 6 to 10) were investigated, E f f e c t of Impurities.  >  The system under i n v e s t i g a t i o n i s made up of reactive metals. Consequently the nature and extent of contamination  must be known.  contaminants are oxygen, nitrogen, hydrogen and hafnium.  The major  The related binary  diagrams of these impurity elements with zirconium are presented i n Appendix B„ Oxygen and nitrogen raise the cc/B transformation temperature making a more stable.  Therefore an immediate e f f e c t of the presence of these two  gases i n t h i s i n v e s t i g a t i o n i s t o affect the r e l a t i v e p o s i t i o n with respect t o temperature of the isothermal curve, A second and probable effect i s to changte the rate of reaction and thus the shape of the curve.  They may introduce phases  which can a l t e r properties such as resistance and hardness. Schwartz and Mallett  23  the f a m i l i a r needles  According to  found i n the microstructure of  Nb  Figure 7.  Isothermal sectionof Zr-Nb-Ti ternary at 700°C (after Whitmore^)  - 12 -  Zr  10  20  30  40  50  % Nb Figure 10. Isothermal s e c t i o n of Zr-Nb-Ti t e r n a r y at 550°C ( a f t e r Whitmore)  quenched zirconium a l l o y s represent hydride phases.  Figure 11 shows these  needles i n a zirconium-niobium-5% t i t a n i u m a l l o y that has been quenched from  Figure 11. Quenched ( 5 % T i ) a l l o y showing needles of hydride phase. Etch HF + HN0 + L a c t i c a c i d , X 1500. 3  - 13 900°C. While contamination by these gases cannot be e n t i r e l y eliminated, i t may be minimised only when the best high-vacuum or inert atmosphere techniques are employed.  These gases are so stable i n zirconium, niobium and titanium  that removal i n t h e i r elemental form at p r a c t i c a l temperatures and pressures i s difficult. The presence of hafnium i s not thought to have any serious effects since i t i s completely soluble i n zirconium.  Thus iodide zirconium which  contains more hafnium and less oxygen than sponge zirconium i s more desirable i n t h i s investigation. Techniques f o r Studying Transformations. Given a reaction involving reactants and products, i t i s possible to distinguish between these because of the difference i n properties.  In choosing  some property to show the nature and rate of the reaction, the fundamental q u a l i t y i s the direct r e l a t i o n between the amount of the property and the amount  24 of reactant or product present.  Cottrell  c a l l s these properties 'capacity  properites' i n contrast t o properties such as density or r e s i s t i v i t y which do not change as f a r as a component i n the bulk i s concerned.  Broadly, capacity  properties employed to show transformation may be divided into f i v e classes: a)  Electrical  -  i n which resistance  b)  Magnetic  -  susceptibility  c)  Optical  -  r e f l e c t i v i t y , metallographic examination  -  e l a s t i c constants (dilatometric), measurements.  d) Mechanical e)  A  may be measured.  microhardness  X-ray d i f f r a c t i o n .  That e l e c t r i c a l resistance i s a capacity property i s shown by the analysis i n Appendix CI. Resistance i s a capacity property but r e s i s t i v i t y i s not.  - 14 For most metallic systems perhaps the e l e c t r i c a l , magnetic and X-ray techniques are the most s e n s i t i v e .  However, the metals and conditions of experiment  impose r e s t r i c t i o n s upon choice of technique.  may  For example, the choice of the  e l e c t r i c a l method with the given c i r c u i t assumes that the specimen can be successfully drawn into a wire. ance was  In t h i s investigation, the e l e c t r i c a l r e s i s t -  chosen as the main technique.  To support resistance data, metallo-  graphic, mechanical (micro-hardness tests) and X-ray d i f f r a c t i o n techniques were used.  II.  1.  Alloy  >EXPERIMENTAL  Preparation The zirconium metal was part o f a stock o f iodide c r y s t a l bar  produced by Foote Mineral Company.  The reported analysis i s given i n Table 1. Table 1.  Analysis of C r y s t a l Bar Zirconium. Element Hf Si Al Mn Mg Fe Cr Ti Ni Ca Cu  o  2  Weight Percent  2.17 0.005 0.002 0.001 0.002 0.002 0.001 0.006 trace  0.003 0.0005 0.01  The titanium c r y s t a l bar produced by the iodide process was supplied by A.D. McKay Company.  In the absence of s p e c i f i c analysis, a t y p i c a l a n a l y s i  25 such as quoted by McQuillan  may prove useful. Table 2.  T y p i c a l Analysis of C r y s t a l Bar Titanium. Element  o  z  N C Fe Ca Al Si Pb Ni Mo 2  • Weight  0.01 0.005 0.03 0.04 trace  0.05 0.03  trace trace trace  - 16  -  Niobium rods of diameter 4.7 mm were puchased from Johnson, Matthey and Company. The accompanying spectre-graphic analysis i s given i n Table 3»  Table 3. Spectrographic Analysis of Niobium Rod. Element  Weight Percent  Ta  0.5 0.0007 0.004 0.012  Ni Fe  Ti  Holes were d r i l l e d i n t h i n s l i c e s of zirconium and titanium which had previously been sawn from the respective bars. the niobium rod.  also sawn from  By c a r e f u l f i l i n g and. weighing, the desired proportion of  each component was melting was  A short rod of niobium was  obtained.  After cleaning with acetone, a compact mass f o r  obtained by i n s e r t i n g the niobium rod into the holes d r i l l e d i n the  other two components.  The mass was then washed again i n acetone.  A diagram of the l e v i t a t i o n melting apparatus of Polonis et a l shown i n Figure 12,  is  Although the l e v i t a t i o n technique employed by Polonis et a l  was  applied, s i g n i f i c a n t changes were made.  A c o i l of s l i g h t l y d i f f e r e n t design  was  designed by Finlayson f o r melting zirconium a l l o y s .  The power supply used was- a 23.5 Kva Lepel valve o s c i l l a t o r .  In order  to suppress the tendency to arc during operation, there should either be a high vacuum or positive pressure.  I t was  more convenient to obtain t h i s condition  with p o s i t i v e pressure using i n e r t atmosphere-.  To achieve t h i s , helium  was  p u r i f i e d by passing over activated charcoal at a pressure of 40 psig and at l i q u i d nitrogen temperature,  A positive pressure of 15 psig was found to be  satisfactory.  The compact unit t o be melted was  suspended by means of a 0.005-inch  - 17 -  ^  Free moctuning brass end ptote I 'Sin. . tfin . J'/.-ir. '/tori « i n . «//<7/7i. rubber O /wy gasket (set in groove in brass p&te)  'Lucite'cylinder-« v o . 0.0 - Ve v o . "thick 7 U L long.  '/a in. efaff? «>/*••/  Induction coil Ve in.. 00 capper tubing o-OXl  »ro//  Capper mould-0.0  NA'ng  to pipe  ,aj  'A i n .  connector f i n diam  rubber  'Lornrer brass plate « J / » « i n thick Power  leads  To pressure ' and vacuum  Figure 12,  , ^Wooden  gouge pump  Argon  Qringgasket Si n . . 6 in.'  platform  inlet Scale t/ii v t v =  »tn.  Diagram of the l e v i t a t i o n melting apparatus of Polonis et a l .  zirconium wire a f f i x e d to a glass rod i n the roof of the chamber.  After  pumping f o r half an hour, the chamber was flushed three times with helium. The chamber was then f i l l e d t o a pressure of 15 p s i g .  Next the inert atmosphere  was gettered by a hot zirconium filament of the same size as the suspension wire.  S t a r t i n g at 30 percent, the power was quickly turned up to 100 percent.  Melting and subsequent mixing o f the i n d i v i d u a l components occurred i n f i v e to ten  seconds.  The power was then slowly reduced to cast the ingot.  A typical  ingot i s shown i n Figure 13.  A l l the ingots appeared bright and clean upon removal from the copper mold.  Weighing i n and out gave a difference of ±0.002 gm f o r a weigh-in of  approximately 6.5 gm f o r each a l l o y . involved i n the a l l o y was n e g l i g i b l e .  Apparently the amount of suspension wire I t was then assumed that the weight of  Figure 13•  A t y p i c a l ingot as cast by l e v i t a t i o n melting.  each component represented the proportion i n i t s respective a l l o y . were designated as Tr 1, 2, 3, i . e . , Ternary 1, 2, 3 . —  The a l l o y s  Those a c t u a l l y used f o r  the isothermal transformation presented i n t h i s report were Tr 24, Tr 25, Tr 29, and Tr 30.  Tr 29 and Tr 30 contained %  15% titanium.  titanium while Tr 24 and Tr 25 contained  The proportion of zirconium to niobium i n a l l was 7:1.5.  During the development of a suitable c o i l there were many unsuccessful attempts to l e v i t a t e and melt batches. to 23. 2,  These attempts are represented by Tr 1  Tr 26, 27 and 28 were rejected when they f a i l e d to draw properly.  Resistance Measurements. Apparatus An apparatus was  assembled to f a c i l i t a t e the determination of specimen  resistance using the c i r c u i t of Rogers'' and Atkins (see Figure 14). comprised  The assembly  a Vacuum furnace, a pumping system, a temperature control u n i t , a  - 19 -  Specimen  Specimen temperature  -O Specimen p o t e n t i a l  <^ 1-100 ohm  |S|  I  I  0.1000 ohm standard p o t e n t i a l Q  40 ohm'  L|,|,|,|J 12 volt Figure 1^.  Diagram of resistance measuring c i r c u i t (a) Ghromel (b) Alumel  - 20 precision potentiometer and a set of lead acid c e l l s .  It i s shown i n Figure 15.  Minor improvements were made on the vacuum furnace designed by Finlayson (see Figures 16 and 17). Short c i r c u i t i n g which interrupted operations often occurred when soldering metal vaporized on to the glass-to-metal s e a l through which a power lead made entry into the vacuum chamber.  Correction  was made by i n s e r t i n g the s e a l at the end of a pipe an inch and a quarter long and thus removing i t from the d i r e c t path of the m e t a l l i c vapour. minor change was the use of a Wilson type seal through which the passed into the chamber.  Another thermocouples  Improved contact between the wire specimen and  thermocouples was achieved by eliminating the clamping device employed by Finlayson.  Holes were d r i l l e d with No. 78 high speed d r i l l s at the ends of  0.004-inch diameter wire specimens, were inserted;  the No. 28 Chromel A-Alumel  thermocouples  a squeeze with suitable p l i e r s ensured good contact. The  specimen wires each 4 cm. long had been previously drawn without anneal from ingots T r 30 and Tr 24.  Two l i m i t i n g factors guided the choice of the wire  diameter of 0.004 inch.  The length was to be s u f f i c i e n t f o r the purposes of  the experiment and yet i t could not be so long that i t s increased surface area threatened a high pick-up of oxygen and nitrogen.  The furnace windings were made with tantalum wire.  Power control  was achieved with a Honeywell C i r c u l a r Scale Controller using a Pt-Pt 10RH thermocouple;  the p o s i t i o n of the l a t t e r i s shown i n Figure 17.  Operating on  a 220V c i r c u i t , temperatures i n the furnace were controlled to • 0.5 C. ;  o  The vacuum system consisted of a mechanical fore pump, an o i l -5 d i f f u s i o n pump and a l i q u i d a i r trap.  Vacuum pressure of better than 10  mm.  Hg was achieved at operating temperatures. The standard r e s i s t o r , S, shown i n Figure 14 was 0,100 ohm.  •  Figure 16  View of main vacuum furnace elements, water cooled can. l i d showing the thermocouple.  - 22 -  4.00". 3.00"  F~7r T  2.00"  6.00"  1.625'  4.15  0  Figure 17.  Diagram of Furnace and Vacuum Chamber Assembly  1,  Brass can  4.  Specimen  7.  Measuring thermocouples ,  2.  Brass l i d with Wilson type s e a l  5•  Specimen-thermocouple contact  8.  Self-gettering furnace. •  3,  Radiation shields  6.  Furnace c o n t r o l thermocouple  9.  Power lead through glass-to-metal s e a l .  - 23 Potentials were measured on a Pye Precision Potentiometer i n conjunction with a Pye Scalamp Galvanometer.  Employing Ohm's law, i f a constant current i s  maintained, then changes i n p o t e n t i a l are proportional to changes i n resistance. Thus i f the connections are made as shown i n the c i r c u i t diagram (Figure 14)* the p o t e n t i a l of the specimen may be measured at a selected temperature. Procedure In order to obtain a homogeneous beta structure, specimens were heated to 900°G f o r one hour.  The furnace power was then reduced so as to  bring the specimen to the desired transformation temperature. ture was reached i n 60 seconds or l e s s .  This tempera-  The specimen was then maintained at  t h i s temperature f o r several hours a f t e r which i t was quenched to room temperature by shutting o f f the power.  A new specimen was inserted and the procedure  was repeated f o r yet a lower transformation temperature. f o r 800°C, 700°G, 600°C, 500°C, 400°C and 300°C,  Runs were accomplished  During the time when the  specimens were held at the above mentioned temperatures, simultaneous readings of p o t e n t i a l and temperature were observed.  To read the p o t e n t i a l a steady  current (68 ma, 70 ma, or more) was passed through the specimen with the aid of a variable resistance u n i t .  A temperature reading followed immediately with  no current passing through. Results and discussion. The 'potentials' data and calculated resistances are tabulated i n Appendix D,  Figures 19 and 20 show the plot of resistance vs time f o r Tr 30  and Tr 24.  Figure 18 shows the plot of resistance vs temperature during slow  heating of a 5% T i a l l o y .  Tentative p a r t i a l isothermal transformation plots  delineating the s t a r t of transformation i n the two alloys are shown i n Figure 21,  The data show that transformation starts at some temperature much below  800°C.  After an incubation period, the body-centered phase begins to transform  ~ 24 -  Figure 18  5.4  Resistance vs Temperature Slowly heated (about 1° every 2 minutes) transformed 5% T i wire specimen  4.1  400  500  600 Temperatur e °C.  700  800  Figure 19a  Resistance vs Time Tr 30 Composition ZrsNb = 7 s l . J L . T i = 5$, of t o t a l weight SpecimenTioniD.genized at 900°C f o r 1 hour Quenched t o temperature indicated _ -  © 500°c  5.04-  - O — O  505 °C  4.94—O'  CM I  o 1o O C cO +> CO -H CO CO  Check run  4.7T  start of 0 -»• a+B transformation marked i n c i r c l e  0=5  405°C  4.6'  4c54-  4.4  o  o  50  100  150  200 Time i n Minutes  250  }<fo"  350  Figure 19b  Resistance vs Time Tr 30  Composition ZrsNb = 7:1.5 T i - % of t o t a l weight Specimen homogenized at 900°C f o r 1 hour  Time i n Minutes  ^  Figure 20a  5  Resistance vs time Tr 24 Composition ZrsNb <= 7.1.5*  Ti  4  Time i n Minutes  -  Vjfc  150  50 100 Incubation Period i n Minutes  - 30 into the close-packed  hexagonal phase.  This incubation period i s smallest f o r  a temperature of 600°C, Given the r e s i s t i v i t i e s of the i n d i v i d u a l components, i t i s impossible to predict the r e s i s t i v i t y of a subsequent a l l o y . values reported correspond  to r e s i s t i v i t i e s that are not unreasonable.  r e s i s t i v i t y values of F i n l a y s o n  1  ( Z r - l 6 % Nb a l l o y ) , Domagala  Nb a l l o y s ) and Domagala, Levinson and McPherson order.  However, the resistance  6  For the  (Zr-7% Nb, Z-=15%  (Zr-Mo a l l o y s ) are of the same  These values l i e between 60 and 120 micro-ohm-cm.  Another trend that  cannot e a s i l y be predicted i s the phase that possesses the larger r e s i s t i v i t y . The values of Finlayson show that above 500°C, the hexagonal alpha phase has higher r e s i s t i v i t y than the body-centered cubic phase;  while below t h i s tempera-  7  6 ture, the reverse i s true.  The reports of Domagala  and Domagala  and  co-  workers show that the r e s i s t i v i t y of the body-centered cubic phase i s highest. Except f o r the f a i r l y constant r e s i s t i v i t y  (resistance as plotted i n Figure  19)  at 800°C, the r e s i s t i v i t y of the body-centered cubic phase i n t h i s i n v e s t i g a t i o n was  lower than that of the hexagonal.  This tendency i s i n agreement with the  f a c t that extrapolation below 600°G leads to a lower body-centered phase resistance f o r a slowly heated wire specimen (Figure 18). resistances of the 15% titanium a l l o y (Tr 24) a l l o y containing only The a)  As would be expected,  are higher than those of the  5%.  curves generally show three main sections:  a f l a t portion representing the resistance of super-cooled  beta  phase, the duration of which marks the extent of the incubation period; b)  a r i s i n g portion representing the progress of transformation, a -* a+8;  c)  another f l a t portion, the value of which i s higher than (a). resistance value i s that of the alpha phase.  The  - 31 Now i f the beta phase undergoes no transformation u n t i l the end of the incubat i o n period, then the resistance of section (a) should be f a i r l y constant. But the 500°C run (Figure 19) f o r example, shows a small v a r i a t i o n although the period of incubation i s reproduced by the check run. v a r i a t i o n was caused by temperature f l u c t u a t i o n s . ohm) corresponds to about 0.406 micro-ohm-cm.  It i s suggested that the  The v a r i a t i o n (0.02 micro-  In order to cause such v a r i a t i o n  i n resistance, the specimen temperature would only have to fluctuate 5°C (see l i n e a r relations of resistance and temperature i n Figures 22 and 23).,  The  specimen was attached to the ends of f l e x i b l e thermocouple wires, the p o s i t i o n ing of which depended only on t h e i r s t i f f n e s s .  Thus the specimen was not  necessarily i n the same position with the furnace from one run to the next. Furthermore, recorded specimen temperature i s only from one small region.  In  view of these positioning d i f f i c u l t i e s , t h i s region could be near the furnace windings i n one run and not so near during the next run.  Since temperature  control i s over the furnace (see p o s i t i o n of control thermocouple i n Figure 17) and not so much over the specimen, a difference of ten degrees could e a s i l y exist between the furnace temperature and the specimen temperature. F i n a l l y , the s e n s i t i v i t y of detection and measurement of resistance i s of i n t e r e s t .  I f the c r i t e r i o n f o r choice of method of measurement i s the  property of capacity, then i t i s assumed that the system — and measuring device —  i . e . , the equipment  i s amenable to e a r l y detection of change.  It i s shown  i n the analysis i n Appendix CI that a transformation as small as one percent can be detected as a measurable change i n resistance. 3,  Micro-hardness Measurements, Procedure Sections less than an eighth of an inch thick were sawn from ingots  Tr 29 and Tr 25;  these alloys contained 5 and 15 percent titanium.  Each s l i c e  130-»  13Qr  Tr 30 (5% T i ) C P . Hex.  Tr 30 (595 T i ) BCC.  120-  slow heat of equilibrium structure  lie-  120- •  1104  from T-T-T data 100.  i  from T-T-T data  Y loo-•  o I o u u  •a  o u o  90-  !>»  80--  I •H  co  •P  slow heating  70-.  •H  CD  co  (4  6d  50  "46*6"  5(fc  6c)o  7do  Temperature (a) BCC Figure 22.  8(fo  °C  9^0  60--  50  40b  500 6ob  7o'o  ibo"  900  Temperature °C (b) C P . Hex.  R e s i s t i v i t i e s of the two structures as found by slow heating and from isothermal transformation data.  \J0 ro  13GV  13c-•  Tr 24 (15% T i ) BCC  12a.  120-.  110..  116.  100.  100-•  Jo  1  s u 1  9a  80..  o  Tr  24 (15% T i )  C.P.  Hex.  9080-  a  n)  -P  7a.  Ul  •H  7a-  CO  0)  PS  6a -  6a50*-  400  500  600  700  800  900  Temperature °C (a) BCC Figure 23.  50-  -—1  400  1  1  500  600  1  -700  Temperature °C (b) C.P. Hex. R e s i s t i v i t i e s of the two structures (isothermal transformation data)  1—  800  900  - 34 was c a r e f u l l y wrapped i n molybdenum f o i l and introduced into a vycor tube containing zirconium chips. and sealed. schedule,  The tube was then evacuated f o r twenty minutes  The specimens were then heat-treated according to the following a l l were homogenized  at 900°C f o r an hour.  Seven capsules were  quickly transferred into a furnace maintained at 700 ± 5 ° C  The capsules  were then quenched i n cold water after 15 minutes, half an hour, one hour, two hours, four, eight and sixteen hours.  Care was taken not break the capsule  A second batch of seven received similar treatment at 600'C.  during quenching,  e  The procedure was repeated f o r 500°C, 400°C and 300°C.  The specimens were  mounted i n l u c i t e , polished and chemically etched with hydrofluoric acid containing- a l i t t l e l a c t i c acid and a few drops of n i t r i c acid. Micro-hardness measurements were taken on each specimen with a Bergsman microhardness t e s t e r mounted on a L e i t z Metallograph. The load employed was 100 gm. and duration of impingement was f i f t e e n seconds. Ten impressions were made on each specimen.  The arithmetic mean and standard  deviation of t h e i r Diamond Pyramid Hardness are plotted i n Figures 24 and 25. On these curves the approximate position i n d i c a t i n g the start of the B —• a+B reaction i s marked. Results and discussion From the above description of procedure i t can be seen that at best 1  the  reactions i n the wire specimens (resistance measurements) are only crudely  reproduced i n the heat-treated pieces.  Dissimilar size and shape of specimens,  poor vacuum i n the heat treatment, and quenching d i f f i c u l t i e s could very e a s i l y affect the reactions.  However, even more important are the differences of 27  opinion on the methods, f o r micro-hardness t e s t i n g .  Wilson  suggests that i n  order to make quantitative measurements of the mechanical properties of the surface layer, much precaution i s necessary.  I t i s necessary to have an  — Figure 24a.  _ - ~  ;  Microhardness Plots - Tr 29 ( 5 % T i )  Time i n Minutes  Y  Time i n Minutes  Time i n Minutes  - 39 absolutely pure- specimen, to anneal perfectly, to e l e c t r o p o l i s h , to handle i t with extreme care before t e s t i n g , and to use a diamond point that has a r e a l point.  I t i s also necessary to eliminate as f a r as practicable, a l l sources  of v i b r a t i o n , and this includes switching o f f the illuminating system while the indentation i s being made.  The effects of grain boundaries  and o r i e n t a t i o n  cannot be neglected, f o r hardness values can show a considerable scatter (as indicated by the large deviations i n the data) i f spread over an area.  In view  of a l l t h i s , interpretation of the reported measurements should be made with reservation.  In some of the curves, i t i s not too d i f f i c u l t to point out f a i r l y  constant i n i t i a l hardness corresponding to the incubation period. general e f f e c t of addition of titanium i s not e a s i l y discerned.  However, the The hardness  data i s included i n Appendix E. 4.  Metallographic Results and discussions Figures 25, 27, 28, 29, 30 and 31 show the results of metallographic  examination.  Figure 26 shows the f a m i l i a r needles of a hydride phase i n an  a l l o y containing 5% titanium.  I t reveals the persistent nature of these  needles, for the specimen has been held at 400°C for half an hour.  According  to the resistance data, no transformation has occurred during t h i s time. other photomicrographs show that the retained beta phase etches white.  The  The  formation of a second phase including the hydride needles can be observed as superimposed dark areas or p a r t i c l e s .  Figures 29 and 30 compare the structures  of a specimen (5% Ti) kept at 600°C f o r ' a week and a transformed wire specimen. D i f f i c u l t y of etching increases with progressive transformation as can be observed  i n Figure 29.  Etching d i f f i c u l t i e s  coupled with the presence of the  hydride phase make the analysis o f these photomicrographs d i f f i c u l t .  - 40 -  F i g u r e 26. (5% T i ) a l l o y h e l d a t 400°C f o r 30 min. P e r s i s t i n g hydride needles and u n t r a n s formed b e t a - X300. E t c h HF+HN0 +lactic acid.  F i g u r e 27.  F i g u r e 28. { % T i ) a l l o y h e l d a t 500°C f o r 4 h r s . Transformed b e t a , needles s t i l l i n evidence X300.  F i g u r e 29.  (5% T i ) a l l o y h e l d a t 500°C f o r 30 m i n . M o s t l y b e t a + needles X300. E t c h HF+HN0 +lactic a c i d . 3  3  ( 5 % T i ) a l l o y held a t 500°C f o r 8 h r s . X800.  - 41  Figure 30.  ( 5 % T i ) a l l o y held at 600°C f o r 1 week. Transformed beta X300.  Figure 31. Wire specimen transformed at 600°C f o r 5 hours X300.  - 42 5.  X-ray D i f f r a c t i o n Procedure Preparation of powder samples from alloys presented d i f f i c u l t i e s .  Diffuse lines indicated that the powder was only p a r t i a l l y annealed even though the annealing temperature was increased to 450°C  o  at the expense of further transformation.  Complete anneal was  This problem was partly solved by  inserting the wire specimens i n the camera and taking d i f f r a c t i o n pictures of these.  The specimens were c a r e f u l l y etched to pin size i n a solution of  hydrofluoric acid and l a c t i c acid.  F i l t e r e d K a copper radiation was  used  0  The best r e s u l t s were obtained by placing the n i c k e l f i l t e r inside the camera, cutting the power down to 25 KV and exposing f o r a period of at least two hours at 15  ma.  Results and discussion The data shown i n Appendix F are f o r the 5% titanium a l l o y held at 600°C f o r only ten minutes and a supposedly transformed specimen at the same temperature.  The specimen held at 600°C f o r ten minutes showed only body-  centered l i n e s .  Unless impurity l i n e s were so weak as to cause them t o b e :  hardly discernible, i t should be assumed that the a l l o y s did not contain large amounts of impurity.  The d-spacings were s l i g h t l y smaller than those determined by Whitmores condition., specimens.  the wire specimens, however, were not necessarily i n the equilibrium furthermore, Whitmore employed powder specimens and not wire The transformed specimen showed hexagonal lines as w e l l as body-  centered l i n e s .  These body-centered lines could be a mixture of beta lines  of the solution and beta l i n e s of niobium or a l l beta lines of niobium. Because the d-spacings are generally low, indexing by comparison with the  - 43 National Bureau of Standards values would be d i f f i c u l t .  However, i f the  specimen were f u l l y transformed,then the body-centered l i n e s must a l l be r e f l e c t i o n s from beta niobium.  A specimen held at 600°C f o r 20 minutes showed the usual bodycentered l i n e s and weak hexagonal l i n e s at the low angle side.  Another  specimen transformed at 500°C f o r 8 hours, showed hexagonal lines and bodycentered l i n e s .  A supposedly transformed 15% titanium a l l o y showed strong  body-centered l i n e s and weak hexagonal ones. angle side were quite d i f f u s e . suitable f o r measurement;  The hexagonal lines at the high  A l l these specimens did not give sharp lines  the r e s u l t i n g pictures were therefore only studied  and compared. If comprehensive  X-ray data were desired then the method to be  employed, i . e . , powder or wire at room temperature, must be anticipated and planned.  This suggestion has only been evident from the d i f f i c u l t i e s  encountered.  For instance, small pieces that were salvaged from the experi-  ment were f i l e d i n order t o obtain powder specimens; discarded i n favour of wire specimens.  the l a t t e r were  Again, i f a transformed wire  specimen  were kept at temperature f o r longer periods, then grain growth would reduce the number of crystals and cause numerous spots without any apparent order on the f i l m .  - 44 III.  The  CONCLUSIONS  r e s u l t s o f t h i s i n v e s t i g a t i o n have shown t h a t t h e e f f e c t o f  s m a l l a d d i t i o n s o f t i t a n i u m on t h e i n c u b a t i o n p e r i o d w h i c h precedes t h e B —* a+3 r e a c t i o n i n an i s o t h e r m a l l y t r a n s f o r m e d z i r c o n i u m - 1 7 . 6 % n i o b i u m a l l o y i s to prolong i t .  T h i s e f f e c t has been demonstrated by e s t a b l i s h i n g  and  comparing t h e r e l a t i o n between t h e i n c u b a t i o n p e r i o d and temperature f o r  two  alloys;  The  i n v e s t i g a t i o n has been a c c o m p l i s h e d p r i m a r i l y by means o f e l e c t r i c a l  t h e f i r s t c o n t a i n i n g 5% t i t a n i u m and t h e second, 1 5 % t i t a n i u m .  r e s i s t a n c e measurements i n c o n j u n c t i o n w i t h m i c r o - h a r d n e s s t e s t s , m e t a l l o graphic  e x a m i n a t i o n and X - r a y d i f f r a c t i o n methods. According  t o e l e c t r i c a l r e s i s t a n c e d a t a , an a l l o y c o n t a i n i n g 5%  t i t a n i u m shows i n c u b a t i o n p e r i o d s  of a p p r o x i m a t e l y 80, 15, 65 and 135  m i n u t e s a t c o r r e s p o n d i n g t e m p e r a t u r e s o f 700°C, 600°C, 500°C and 400°C. minimum i n t h e t i m e i s i n t h e v i c i n i t y of 600°C, e x a c t p o s i t i o n more d a t a i s n e c e s s a r y .  The  I n order t o e s t a b l i s h i t s  The a d d i t i o n of 15% t i t a n i u m t o t h e  z i r c o n i u m - 1 7 . 6 % n i o b i u m a l l o y caused t h e i n c u b a t i o n p e r i o d t o be e x t e n d e d . At 600°C, t h i s p e r i o d i s a p p r o x i m a t e l y 25 m i n u t e s as compared t o t h e 15 minutes o b s e r v e d i n a 5% t i t a n i u m a l l o y . t h e minimum i n t h e t i m e i s unknown.  Here t o o , t h e p r e c i s e p o s i t i o n o f  I t i s r e a s o n a b l e t o suppose t h a t i t  e x i s t s a t some temperature s l i g h t l y below t h a t o f t h e a l l o y c o n t a i n i n g 5% titanium.  The i n c r e a s e i n t h e i n c u b a t i o n p e r i o d shown b y t h e a d d i t i o n o f  15% t i t a n i u m i s not u n i f o r m .  F o r above and below 600°C, t h e i n t e r v a l  d e c r e a s e s p r o g r e s s i v e l y so t h a t a t some t e m p e r a t u r e above 700°C and below 400°C, i t approaches z e r o .  The intermediate  e l e c t r i c a l r e s i s t a n c e d a t a does n o t i n d i c a t e t h e presence o f products during the ensuing isothermal transformation.  However,  - 45 i t i s believed that more data is necessary to e s t a b l i s h t h i s f a c t . Micro-hardness t e s t s r e v e a l that although the primary e f f e c t of small additions of titanium i s to prolong the incubation period, the period of incubation i s longer than the value obtained from e l e c t r i c a l resistance. For, at 600°C, the a l l o y containing 5% titanium shows an incubation period  of  approximately 30 minutes as compared to the 15 minutes obtained from resistance data.  The micro-hardness tests show that when the amount of titanium i s  increased to 15%, the incubation period becomes 40 minutes.  The  observation  of a longer incubation period i n the micro-hardness specimens i s not unreasonable since the shape, size and heat-treatment of these did not exactly duplicate those of the resistance specimens.  Metallographic and X-ray d i f f r a c t i o n data are l i m i t e d .  Although they  do not c l e a r l y e s t a b l i s h the l i m i t s of incubation periods at the various temperatures, the data do not c o n f l i c t with those obtained by e l e c t r i c a l resistance and micro-hardness measurements.  That a l l o y additions should generally lengthen the incubation period i s i n keeping with modern views on a l l o y i n g theory and p r a c t i c e . studies of Domagala  6  Recent  on zirconium-niobium a l l o y s and of Domagala and coworkers  on zirconium-molybdenum a l l o y s have been c i t e d as showing this general e f f e c t .  Furthermore, the d e s i r a b i l i t y of observing isothermal t i o n with resistance measurements has been c l e a r l y demonstrated.  transformaIn view of  i t s high s e n s i t i v i t y and ease of measurement, e l e c t r i c a l resistance determinations could form the basis of further experimental  work on t h i s system.  Micro-hardness, metallographic and X-ray d i f f r a c t i o n methods would prove invaluable i n these studies.  7  - 46 -  APPENDIX A Related Phase Diagrams  2000  400 I Zr 1.  I  I  20  I  I  40  I  I  60  1  1 80  The zirconium-titanium c o n s t i t u t i o n a l diagram (after Fast and Hayes et a l )  1  1  100  APPENDIX A (cont'd.)  2,  The titanium-niobium c o n s t i t u t i o n a l diagram (after Hansen et a l )  APPENDIX B Related Phase Diagrams (Impurities)  Oxygen Wt.%  2  10  5  15  30  50  Oxygen At.% 1.  The zirconium-oxygen system  .25  , 70  APPENDIX B (cont'd.)  Nitrogen At.% 25  40  1  7  r  /  2700  /  / 2300  /  /  /  L +. ZrN  ^  J 1900  a + B  1500  a + ZrN  1100 h ZrN-* \  700 5 Nitrogen 2.  J  10 Wt.%  The zirconium-nitrogen system  I  13  3.  The zirconium-hydrogen system  - 51 " APPENDIX CI To show that e l e c t r i c a l resistance as employed i n t h i s i n v e s t i g a t i o n i s a 'capacity property'.  i\ — K f ^ t — v - \  I  F.C.C.  L  1-  Figure 1.  JL  =  then  R  (No transformation)  R^ R  FCC  S  FCC  +  & FCC  R  n  ^BCC +  R  2  ^  6  s p e c i f i c conductance is -  m.  FCC ^  R  BCC +  = JL + j&  ^FCC  area marked i n Figure 1  A 6^'FCCA  (Some transformation)  /  A  where S  = si A S  Then  J  where JL ' i s length of block  A  If  — —  A transformation block showing F.C.C. changing into B.C.C. (Resistance i n S e r i e s ) .  If the resistance R  /  F.C.C.  A  +  R  FCC  ^RHBCC f! ^2 *2  +  2, ^ BCG  A  s  >FCC& 3 A  F C n  x  - 52 Appendix C I (cont'd.)  F.C.C. B. C. C»  ^ ^l^'  v////////7//////  F i g u r e 2. , T r a n s f o r m i n g b l o c k  The  (resistance i n p a r a l l e l )  condition i n Figure 2 i s equivalent  Ri  dR  /y  R =  R  1 +  t o r e s i s t a n c e s R]_ and R  R  2  in parallel  2  (Ri R ) - RlR +  2  2  (Ri+R )  2  2  2  R"  t h i s i s a perfect  square  (R R )' 1 +  therefore  The  above a n a l y s e s  2  > 0  show t h a t a change i n t h e amount o f some phase i n t h e  b l o c k w i l l r e g i s t e r a change i n r e s i s t a n c e f o r t h e whole  block.  - 53 APPENDIX CII  In order to estimate the inherent error i n the f i x i n g of the incubat i o n period, i t would be necessary to know the degree pf response i n the potentiometer —  i . e . the amount of transformation that causes a detectable  change i n resistance.  Such error i s estimated i n the ensuing analysis. Resistances  /  M 1  71  •777;  IT  (a)  (b)  Series  Parallel  Let  r  and  r e s i s t i v i t y of phase 1 (say bcc) b e ^ ^ ohm cm,  and  r e s i s t i v i t y of phase 2 (c.p.hex) be p2 ohm cm.  0  (c)  Actual state of affairs i n specimen  ohms be the detectable change i n resistance;  Suppose the shaded region x as shown above has transformed, the the resistance of the specimen = R i + Rg ^series as i n (a) a b o v e j  xp,  = (/•- x)fi  +  (1)  where A i s the cross s e c t i o n a l area and The  /, the length of the wire specimen.  change i n resistance  =  (new resistance) - ( i n i t i a l resistance)  A  A  A  A  A (2)  A  - 54 Appendix CII (Cont'd.) Minimum x detectable by change i n resistance i s X Q *£ ( p  where If a i s the f r a c t i o n then  a  - ft )  =  r  (3)  G  transformed, a  = xA  =  x  (4)  Therefore minimum a detectable by resistance measurement i s a o  (  where a  n  =  Xp  L  which by substitution from (3) =  now  fL fc,  =  R  i ro r  I  a  1  (5)  2  A and  A where R and  2  i s the t o t a l resistance after transformation i s complete, i . e . x = ,  R]_ i s the i n i t i a l resistance before transformation s t a r t s , i . e .  x =  Employing the above expressions f o r R]_ and R , (5) becomes 2  a  o =  R  - R-L  2  =  l r  iR  Q  v  o - iR]_  where V i s potentiometer reading.  o  V - v 2  where i i s current  x  Now suppose a change of 0.001 m i l l i v o l t s can be read on the potentiometer, then at say 600°C (Figure 19),  a* =  =  0.001 5.12 - 5.01 0.001  ^  0.01  - 55 Appendix CII (Cont'd.) Therefore a resistance measurement detects a transformation of 1% i n the wire specimen. If the transformation i s as shown i n (b), then the resistances are parallel.  I f the small transformed section has area a, then the resistance  RQ_ of the specimen i s : R  =/l (*i =  where  - i - Y )  +  (6)  1  P\ (A - a)  1  -i-l  thus  R  = f(  - )  A  a  a  +  T  i n i t i a l resistance  =  O  jj A  Therefore change i n resistance = ( \(A ( A - a)  + _ aa_^"^ T  -  P\ ^ A  (7)  Let a be the f r a c t i o n transformed, then a  = jta =  J3k  a A  thus a detectable i s a 1  where a  Q  Q  - ja^ A  (8)  I f the minimum a detectable i s a , c  then from ( 7 ) , T (A - a) where  r  0  +  a 1^ ft I h  - r  i s the minimum detectable change i n resistance.  (9) Q  - 56 Appendix CII (cont'd.) To find a  i n terms of r , Equation (9) becomes^  II A - a  + ao.'Y -.  [~7r  K)  l  ft A - a )  1  + apfiT  c  L~~IT* 0  1  -  J  Q  ^+  a p 0  = £o  - ft •  flfr  7(A - a  £  A  (A i a ) ^ + a ^ ,  or  fit =  1  0  A  6  |  (A - >p-)ft,+ aft = T r  ^ -ao(ft-fi) a  0  -fifi.  +  ^ J "  (roA +  1  ^  r  therefore  1  a.  o  A  +  P,  p,I'l /.  -  r A + fit o P2  r iVsA +M-  L  ( f » f  r  oA +  (*  J ft£  L  r A 0  (^-  p,) (r A  +  ftl)  (10)  - 57 Appendix CII (cont'd.)  Now  |?  =  A E-^ where R]_ i s i n i t i a l resistance, i . e . , a = 0  =  A  Y_l where V i s p o t e n t i a l and i ,  I Similarly and  D r  Q  -  current.  1  A  =  Thus from Equation  (10), a =/A  \ VQ A i / %  Q  JL^  v (V  2  2  1 £._(V  2  - V) X  1 ^VpA - AVij  Vo  - V^Vo  + V]_)  (V - Vi) (V + Vi) Thus at 600°C (5% titanium a l l o y ) 2  V = V = V-|_ =  0.001 mv. .. 5.12 mv. 5.01 -: mv.  a  5.12(0.001) 0.11(5.011)  2  and  =  0  0.01 Therefore resistance measurement detects a transformation of 1% of the specimen. The actual process of transformation, however, w i l l be more l i k e that shown i n ( c ) , i . e . , several nucleation s i t e s .  The probable value of a  0  w i l l therefore l i e between that of 'series' 'treatment and that of the ' p a r a l l e l ' treatment.  According to the above analysis, 1% i s the detectable  volume of transformation.  fractional  APPENDIX D Resistance Data Resistance values are i n ohms x 10' Time i s i n hours. Tr 30 - % titanium a l l o y ± indicates fresh specimen. 802°C  A  t  R  0.0 0.083 0.166  5.215 5.215 5.215 5.215 5.215 5.22 5.22 5.215 5.215 5.215 5.215 5.215  0.500 0.75  1.00  1.25 1.75 2.00 2.750 3.00 4.00  t  704°C * R  0.0 0.083 0.167 0.183 0.416 0.500 0.584 0.750 0.917 1.085 1.500 1.670 1.750 2.250 4.00 6.00 8.00  5.18 5.18 5.17 5.16 5.17 5.16 5.17 5.16 5.15 5.145 5.14 5.19 5.25 5.19 5.195 . 5.20 5.20  700°C  6oo°c  t  R  0.0 0.5 1.25 1.50 1.583 1.666 2.0 2.5 4.0  5.14 5.14 5.14 5.14 5.14 5.16 5.21 5.21 5.21  t 0.0 0.083  0.25  0.33 0.50 0.583 0.667 1.0 1.25 2.83  a R  609°C ' t  4 R  5.01 5.01 5.01 5.04 5.07 5.085 5.10 5.10 5.11 5.11  0.0 0.083  5.015 5.015 5.018 5.045 5.06 5.07 5.06 5.065 5.065  0.25 0.50  0.584 0.75 1.0 1.5 2.0  t  505°C A R  0.0  0.25  0.33  0.50  0.75 1.00  1.25  1.5 1.75 2.0 2.5 2.75 3.0 3.5 3.66 4.0 4.25  4.9 4.895 4.895 4.890 4.865 4.860 4.89  4.92  4.95 4.95 4.95 4.95 4.93 4.93 4.96 4.95 4.95  t  500°C R  4.87 4.87 0.5 4.87 0.75 1.0 4.87 1.25 4.887 1.5 4.915 4.92 1.75 1.833 4.92 2.00 4.96 2.66 5.00 2.833 5.01 3.0 5.01 3.33 5.015  0.0  t  405 °C ± R  0.0 0.166 0.25 0.50 0.75 1.00 1.5 2.0 2.083 2.25 2.33  2.417 2.5 2.833 3.5 4.0 5.0 6.0 10.0  4.495 4.495 4.495 4.496 4.495 4.465 4.465 4.465 4.495 4.495 4.49 4.515 4.54 4.535 4.55 4.58 4.6 4.625 4.58  APPENDIX D (cont'd.) Tr 24 - 15% Titanium A l l o y Slow heating of transformed 5% T i specimen :  701°C t 0.0 0.083 0.25 0.500 0.750 1.50 1.584 1.66 1.75 1.833 2.33 3.0 4.0 5.0 7.0 8.0  R 5.62 5.62 5,62 5.615 5.615 5.62 5.62 5.63 5.665 5.67 5.69 5.72 5.75 5.77 5.78 5.78  598°C t 0.0 0.083 0.166 0.25 0.33 0.5 0.75 1.0 1.5 2.0 2.5 3.0 4.0 5.0  •&  R 5.31 5.31 5.315 5.315 5.29 5.35 5.41 5.41 5.47 5.49 5.47 5.495 5.495 5.50  \. 600°C t R  o.o 0.25 0.33 0.5 0.583 0.833 1.33 1.75 2.0 3.0 4.0  5.34 5.34 5.39 5.415 5.41 5.445 5.51 5.515 5.515 5.491 5.493  500°C t 0.0 0.25 0.50 0.75 1.0 1.166 1.25 1.5 2.75 3.0 3.5 3.75 4.0 4.25 4.5  t R 5.17 5.17 5.17 5.17 5.17 5.171 5.17 5.18 5.21 5.215 5.225 5.23 5.231 5.23 5.235  500°C t 0.0 0.25 0.5 0.75 1.0 1.33 2.0 2.166 2.33 2.5 3.0 5.0  R 5.185 5.185 5.185 5.185 5.185 5.189 5.2 5.21 5.215 5.22 5.23 5.235  400°C t 0.0 0.166 0.33 0.75 1.0 1.5 1.75 2.0 2.25 2.50 2.833 3.0 3.25 3.5 4.0 8.0  R 4.98 4.98  4.98 4.985 5.07 5.10 5.10 5.09 5.09 5.09 5.16  t 201°C 305°C 400° C 441° C 473 °C 500 °C 549°C 600°C 619°C 625 °C 630 °C 650°C 670 °C  703 °c  801° C  900 °c  R 4.1 4.31 4.51 4.517 4.61 4.685 4.74 4.81 4.74 4.66 4.65 4.715 4.775 4.94 5.20 5.61  APPENDIX E Micro-hardness Data Load 100 grams Duration of impingement 15 seconds Tr 29 - 5% titanium a l l o y  , n — Hardness No„(DPH) kg/mm. Average of 10 impressions 11  Temperature 700 °C  Duration of Heat Treatment 15 minutes 30 minutes .1 hour 2 hours 4 hours 8 hours 16 hours  197.1  j  199.2 196,6 199.5 194.2 208.8 204  Standard . Deviation ± 4.9 ± 9.8 ±12.5 ± 8.6 ±25.5 ±13.5  600 °C  15 minutes 30 minutes 1. hour 2 hours 4 hours 8 hours 16 hours  204.3 194.4 212,5 215.4 218,8 222 o 5 216,4  ±19.5 ±10,4 ±10 ±13.1 ± 4.5 ±14.2 ±15.8  500°C  15 30 1 2 4 8  minutes minutes hour hours hours hours 16 hours  224.8 223,6 223.2 224,6 231.7 232,0 219,9  ±17.7 ± 7.4 ±16,7 ±12.8 ±24.8 ±18 ±26.2  400° C  30 minutes 1 hour 2 hours 4 hours 8 hours 16 hours  215.2 218,3 224,0 234.0 235.5 236,1  ±12.8 ± 6 ±23.1 ±25.2 ±15.6 ±18.8  300 °C  15 minutes 30 minutes 1 hour 2 hours 4 hours 8 hours 16 hours  226,7 222 o 3 220,8 215.4 233.6 242.3 220.1  ±14.3 ±12.6 ±10,7 ±18.6 ±16.7 ±14.6 ±20.1  - 61 Appendix E (cont'd.) Micro-hardness Data Tr 25 - 15% titanium a l l o y  Temperature  Duration of Heat Treatment  Hardness No.(DPH) kg/mm.  2  Standard deviation  700 °C  15 30 1 4  minutes minutes hour hours  219.6 218.5 217.4 229.5  ± 4.8 ±14.8 ±11.9 ±13.8  600 °C  15 30 1 2 4 8  minutes minutes hour hours hours hours  208.6 206.5 208.8 224.8 232.0  233  ± 4.9 ±10.2 ± 8.7 ± 9 ±10.8 ±30  500 °C  15 30 1 2 4 8 16 32  minutes minutes hour hours hours hours hours hours  206.5 215.9 222.6 203.1 201.2 199.6 239.0 229.3  ± 8.4 ± 8 ±14.5 ±10.3 ± 8.6 ±18.7 ±16.6 ±17.1  400°C  15 30 1 2 4  minutes minutes hour hours hours  209.1 214.2 218.6 217.0 221.8  ±11.7" ±15.6 ±10.1 ±6 ± 9.3  APPENDIX F d-Spacings (Angstroms) of Zr-Nb-5% T i a l l o y - wire specimens  Index  NBS  After Whitmore 5.6% T i ; 17.6% Nb  100 a 002 a 101 a  2.798 2.573 2.459  2.769 2.540 2.434  102 a 003 a  1.894  1.878  110 a 103  1.616 1.463  1.606 1.452  200 112 201 004 202 113  1.399 : 1.368 1.350 1.287 1.230  1.389 1.361 1.340 1.278 1.221  203 a 210 a 21i: a 114 a  1.084 1.059 1.036 1.006  1.077 1.051 1.029 1.001  105 204 300 213  a a a a •  0.966 0.947 0.933 0.900  302 106 214 220  a' a a a  0.877 0.820  bcc bcc  bcc  bcc bee  bcc  bcc  a a a a a a  ;  :  i  0.960 " 0.941 0.928 0.896 0.873 0.819 0.804  Held at 600 °C f o r ten minutes i d e n t i f i e d as body-centered cubic phase  Transformed at 600°C 5% T i ; 17.6% Nb  2.751 2.548 2.458 2.358 1.882 1.741 1.665 1.606 1.460 1.420 1.390 1.362 1.343 1.276 1.234 1.172 1.107 1.105 1.080 1.052 1.031 1.004 0.975 0.961 0.944 0.929 0.896 0.889 0.873 0.825 0.815 0.805 2.473 1.734 1.437 1.245 1.114 1.014 0.941) 0.942) 0.831) 0.832) 0.787  53 BIBLIOGRAPHY  1.  Finlayson, M.J., Isothermal Transformation i n Eutectoid Zirconium Niobium Alloys, M.A.Sc. Thesis, University of B r i t i s h Columbia (1957).  2.  Whitmore, B.C., Zirconium-Rich Corner of the Zirconium-Titanium-Niobium Constitutional Diagram. M.A.Sc.. Thesis, University of B r i t i s h Columbia (1958).  3.  Lustman, B., and Kerze, F., editors, The Metallurgy of Zirconium, National Nuclear Energy Series, McGraw-Hill (1955).  4.  P f e i l , P.C.L., A C r i t i c a l Review of the Alloying Behaviour of Zirconium, A.E.R.E. - M/TN-11, March 1950.  5.  P f e i l , P.C.L., A Discussion of the Factors A f f e c t i n g the Constitution of Zirconium Alloys, A.E.R.E. M/R 960, June 27, 1952.  6.  Domagala, R.F., A Study of the Mechanisms of Heat Treatment of Zirconium Base Alloys, Armour Research.Foundation Report f o r A.E.C., July 17, 1956.  7.  Domagala, R.F., Levinson, D.W., and McPherson, D.J., Transformation Kinetics and Mechanical Properties of Zr-Mo Alloys, A.I.M.E. Trans., 209. 1191.  8.  Austin, J.B., and Rickett, R.L.,  9.  Mishima, T., Hasiguti, R. and Kimura,' Y., Proc. F i r s t World Met. Conf., A.S.M., 668, (1951).  A.I.M.E. Trans., _ _ 5 , 396 (1939).  10.  Mcintosh, A.B.,  J . Inst. Metals 85, 1855, A p r i l 1957.  11.  Anderson, C.T., Hayes, E.T., Roberson, A.H. and K r o l l , W.T., A Preliminary Survey'of Zirconium A l l o y s , U.S. Bureau of Mines Investigations, No. 4658.  12.  Simcoe, C.R.,  and Mudge, W.L.  J r . , A.E.C. Report No. WAPD-38, November  21, 1951. 13.  Keeler, J.H., A.E.C. Report No. S0-2504, January 5, 1952.  14.  L i t t o n , F.B.,  15.  Hodge, E.S., A.E.C. Report No. T 1D-5061, January 31, 1952.  16.  Rogers, B.A.,  17.  Domagala, R.F.,  18.  Bychkov, Yu, F., Rozanov, A.N. and Skorov, D.M., Atomnaya Energiya 2, 146-157, (1957). Fast, J.D., The Transition Point Diagram of the Zirconium-Titanium System, Rec. Trav. Chijn., 58, 973 (1939).  19.  Iron Age, 167, 95-99 and 112-114,  and Atkins, D.F.,  (1951).  A.I.M.E. Trans. 203. 1034, (1955).  and McPherson, D.J., A.I.M.E. Trans. 206, 620 (1956).  64 Bibliography (cont'd.) 20.  Hayes, E.T., Roberson, A.H. and Paasche, O.G., Zirconium-Titanium System, Constitutional Diagram and Properties, U.S. Bureau of Mines Investigations, 4826, November .1951.  21.  Hansen, M., Kamen, E.L., Kessler, H.D., and McPherson, D.J., Systems Titanium-Molybdenum and Titanium-Columbium, A.I.M.E. Trans., 191, 881 (195D  22.  Rhines, F.N., Phase Diagrams i n Metallurgy, McGraw-Hill, (1956).  23.  Schwartz, CM., and Mallett, M.W.,  Observations on the Behaviour of  Hydrogen i n Zirconium, A.S.M. Tfansi', 46,' 64O, 1954. 24.  C o t t r e l l , A.H., Theoretical S t r u c t u r a l Metallurgy, Edward Arnold (1955).  25.  McQuillan, M.K., and McQuillan, A.D., Titanium, Chapt. 10, 335, Butterworths S c i e n t i f i c Publications (1956).  26.  Polonis, D.H., Butters, R.G., and Parr, J.G., Research 7, No. 2 (1954).  27.  Properties of M e t a l l i c Surfaces,Inst. Metals, 356, (1953).  

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