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The effect of interstitial elements on the mechanical properties of tantalum at low temperature Lawson, Victor Bruce 1961

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THE EFFECT OF INTERSTITIAL ELEMENTS ON THE MECHANICAL PROPERTIES OF TANTALUM AT LOW TEMPERATURES by VICTOR BRUCE LAWSON 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 t h e s i s as conforming to the standard r e q u i r e d from candidates f o r the degree of MASTER OF APPLIED SCIENCE Members of the Department of Mining and M e t a l l u r g y THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1961 In presenting t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree th a t the L i b r a r y s h a l l make agree that permission f o r extensive copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood t h a t copying or p u b l i 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 g a i n s h a l l not be allowed without my w r i t t e n permission. i t f r e e l y a v a i l a b l e f o r reference and study. I f u r t h e r Department The U n i v e r s i t y of B r i t i s h Columbia, Vancouver $, Canada. . ABSTRACT An i n v e s t i g a t i o n of the low temperature t e n s i l e p r o p e r t i e s of tantalum and of tantalum con t a i n i n g added i n t e r s t i t i a l s was c a r r i e d out. Added n i t r o g e n , oxygen, and hydrogen were found to increase the l e v e l of the y i e l d point s t r e s s r e l a t i v e to that of the s t a r t i n g m a t e r i a l . The elongation of m a t e r i a l with added n i t r o g e n and oxygen e x h i b i t e d l e s s elongation at room temperature than d i d the pure m a t e r i a l , but at —196°C i t showed more e l o n g a t i o n . Plydrogen embrittlement was observed i n the m a t e r i a l with added hydrogen. I t was demonstrated that the t e n s i l e p r o p e r t i e s of tantalum were s e n s i t i v e to s t r a i n r a t e . A t r a n s i t i o n from a d u c t i l e - t o - l e s s d u c t i l e type of behaviour was found on decreas ing the temperature. The t r a n s i t i o n temperature a l s o was found to be s t r a i n r a t e s e n s i t i v e . ACKNOWLEDGEMENTS The author g r a t e f u l l y acknowledges the s u p e r v i s i o n and encouragement of Dr c J<,A0 Lund and Professor W0M0 Armstrong and wishes to thank Mr 0 R 0G 0 B u t t e r s , Mr 0 Wm0 Cross, and Mr 0 R 0 R i c h t e r f o r t h e i r t e c h n i c a l advice and a s s i s t a n c e during t h i s investiga=> t i o n 0 The author i s a l s o indebted to Dr„ Eo Teghtsoonian and f e l l o w graduate students f o r h e l p f u l discussions„ The work was financed by Research Grant No c 7510-36 provided by the Defence Research Board of Canada 0 TABLE OF CONTENTS Page I INTRODUCTION A» G©ITG 1^ (9.3- o a a a a o o a o o a o a o o e a o a o a a o a a s o o o o o a O Q Q O O X. B o ThGOl *y 0 0 9 e o * O 0 0 O 0 0 O O 0 0 0 0 O O O 0 O 0 O 0 0 0 O 0 0 0 0 0 0 0 C 0 2 1. D u ' c t i l e - t o - B r i t t l e T r a n s i t i o n ...... 3 2. Temperature Dependence of Y i e l d S t r e s s .. 6 I I PREVIOUS WORK ON TANTALUM A. The E f f e c t of Hydrogen . . . . . . . . . . . o o o 15 B. The E f f e c t of Nitrogen ..................... . 15 C a Ttl© Ef f © C t O f OXy^GIT. © o o o o o o o o o o o o o a G G o o o o o o o X8 D o T h-6 E f f 6 C t O f A X I* o o o « « « o o o o a o « « « A o « o o « * o « e « o X^ I I I EXPERIMENTAL_ A o Mcl t ©I* X 31 S O O » O Q O * O O O O » O O O O O O O » O O O O » » O O O O O O O O O 20 B o SpGciniGn Pi*Gpsrs"tion o o o o » o o o o o o o o o « o o o o o o o o o 20 1 o Lot 1M 20 2 o I j O t 2Mi O O O O O O O O O O O O a O O O O O O O O O O O O O O O O O O O O O 2^ 4" 3 o XlOtS XWC 3.nCl 2WC a G c a o a a a » o e o « G i > « o © o « o o o o 27 0 o G e l S Add 111O X 1 S a o a o o a o o o a o o e a a o s a a c c a a o a o a a o o G 23 Do Testing Procedure 32 IV EXPERIMENTAL RESULTS AND OBSERVATIONS A. Results of I n i t i a l Lots of Tantalum ......... 35 1„ Lot 1M (annealed Murex Tantalum) ........ 35 2. Lot 2M (contaminated Murex Tantalum) o . . . *+0 3 . Lot 1WC. (Pre-cut T e n s i l e Specimens from Wah Chang Sheet) ................... h-2 k0 Lot 2WC (Wah Chang Sheet) ............... h-2 B. R e s u l t s of I n i t i a l Lots of Tantalum ......... M+ 1. Nitrogen A d d i t i o n s M+ 2. The Oxygen A d d i t i o n .......... ......... *+9 3. The Hydrogen A d d i t i o n ................... *+9 Co Tlr© Acctii*cicy of R©sTJ.I.ts » o o o o o o o o » i > o » » » o » o r > » o 52 . V DISCUSSION A» Y X G I C I P o i n t R©suXts o a » « o o o » » » » « o o o o o » « o o e o o o ^ 3*7 Bo D t l C t i l X t y ] R © S \ X l t S a a s o o a a o o a a o a a a a a a e a a o a o o a a 62 VI SUMMARY AND CONCLUSION 67 V I I RECOMMENDATIONS FOR FUTURE WORK ... 68 V I I I BIBLIOGRAPHY 70 IX APPENDICES 9 0 9 o a * o o a a o * o o o o o o o o * * o « » a a » * » o « * o * o » o « o 0 73 FIGURES No. Page 1. Y i e l d Stress and Elongation of Tantalum ............... . 12 2 0 Ultimate Stress and Reduction i n Area ....... o . . . . . . . . . o 13 3o Hardening of Tantalum by Gases ............. 0.......... . 16 h. Mechanical Properties of Tantalum containing Nitrogen 0 o 17 5. E f f e c t of Nitrogen on the Stress-Strain Curves of o 17 6. Dependence of Mechanical Properties of Tantalum on *t tl. 6 0 ^ 6 rX C 0"fc 6 IX. "t Q » a 9 O » O O a s * O O 9 9 * O 9 O O O » 9 » C > O 9 » 0 » f t < 9 * 9 C > O o 18 7. Dependence of the E l a s t i c Modulus on the Oxygen Content .18 8. Specimen Holder and Filament i n Zone Refiner . 22 9o Dimensions of Tensile Specimen o . o . . o o o . o o . o . o o o . . . . o . o o 23 10 o The Specxmen Punch and Die o . e . o « o o o » o o o . . o G o o o a o o © o o o . . 25 l l o Modified Sintering Furnace showing Vacuum System . 25 12 o Modified Vacuum Annealing Furnace showing Manometer o 29 13 o The Modification of Instron Tensile Tester . 33 l h a Dewer Flask with Liquid Nitrogen Container . . . . . . o . o o . . o 33 15. Typical Load-Elongation Curves ........................ o 36 16 o Properties Versus Temperature for Tantalum Lot IM o 38 17 o Specimen showing Liider 1 s Band . . . . . . . . . . . . . . . . . . . . o . . . . . 39 18 o Properties Versus Temperature for Tantalum Lot 2M . . 0 . o o hi 19. Properties Versus Temperature f o r Tantalum Lot 1WC .. 0. . ^3 20. Typxc3.1 Brok@n Sp©cim©xxs » o o o o o e i » # « » o » c » a o Q » e < > o o o o « o o o o o . hh 21. Properties Versus Temperature for Tantalum Lot 2WC o o . . . h5 22. Yield-Point Stress Versus Temperature for Tantalum P 3_ \1 S NxtrO^G IX. 0 © » O 0 O O O 0 , 3 0 0 0 » 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 . h7 23. Elongation Versus Temperature for Tantalum plus FIGURES No. Page 2 h B Yield-Point Stress and Elongation Versus Temperature 2 5o Yield-Point Stress and Elongation Versus Temperature plus 299 PP^° Hyclro^Gn ©00000000000000000000*00000000000 ^1 26o Photograph of Lines found i n Luder's Bands e 0o<> ° < . » 0 ° « 0 o o 0 55 2*7o Typicsl 4^1 c r o s true tur G s O O Q O O O O O O O O O O O O « » O O O O O » C » 3 Q ® O 9 O O O 280 Yield-Point Stress Versus Nitrogen and Oxygen Contents „ 59 29o Yield-Point Stress Versus Total I n t e r s t i t i a l Content 0 o o 61 30. Slopes of Yield-Point Stress Versus Total I n t e r s t i t i a l Content Lines Versus Temperature o » . o o o o o 0 0 o » o o o o o . 0 0 0 0 0 61 TABLES No. Page I The Room Temperature Data of Annealed Tantalum. 0 .»0 . . . 9 II The Chemical Analysis of Tantalum . 0................ 0. 1 0 III Effect of Various Gases on Tantalum at Elevated ^ T 6IH P© 1*9 "till* 6 S 3 a > » 0 O 0 » O 0 O 0 0 O O O 0 0 » O O » 0 0 9 0 O 0 » » O 0 0 0 a O » O O » O O -L*H" IV Chemical Analysis of Tantalum ........................ 2 1 V Analysis of Tantalum by Ledoux and Company ..... ...... 3 1 VI Analysis of Tantalum by Wah Chang Corporation ........ 3 1 VII Appendix A - The Results of Tensile Tests on T 3. n't 3 ItXm Xl O "t o o o e o a < > a « o o « o o o o c » o o < 3 « a o 6 C i 7 3 VIII Appendix B - The Results of Work Hardening and Aging . 75 IX Appendix C = The Results of Tensile Tests on T3.n"tcllL"Lini LO"t o o o o o o o a o o o o o o o o o o o o o o o o o 7 ^ X Appendix D - The Results of Tensile Tests on T 3ri"t 9. XUirL!. XjO"t 3-WC o o o o » o o o t > o o » » « o o a » e o o o o o 7^ XI Appendix E - The Results of Tensile Tests on TcintciXuni Lot 2W0 o c - o o « 3 o o » o o o o o « o o o o » « o « o 8 0 XII Appendix F - The Results of Tensile Tests on Tantalum Lot 1WC> Batch 1 ................ 81 XIII The Results of Tensile Tests on Tantalum Lot 2WC, Batch 2 ................ 8 1 XIV The Results of Tensile Tests on Tantalum Lot 2WC, Batch 3 . . 8 2 XV The Results of Tensile Tests on Tantalum Lot 2WC, Batch h . . . . . . . . . . . . . . . . 8 2 XVI The Results of Tensile Tests on Tantalum Lot 2WC%Ba.tch 5 . . . . . . . . . . . . o o . . 8 3 XVII The Results of Tensile Tests on Tantalum Lot 2WC,Batch 6 . . . . . . . . . . . . . . . . 8 3 XVIII The Results of Tensile Tests on Tantalum Lot 2WC,Batch 7 . . . . . . . . . . . . . . . . Qh TABLES No. Page XIX Appendix G - The Results of Tensile Tests on Tantalum Lot 2WC, Batch 8 85 XX Appendix H - The Results of Tensile Tests on Tantalum Lot 2WC, Batch 9 86 THE EFFECT OF INTERSTITIAL ELEMENTS ON THE MECHANICAL PROPERTIES OF TANTALUM AT LOW TEMPERATURES I INTRODUCTION A. GENERAL The increasing demand for materials having special high-temperature properties has led to considerable interest in refractory metals and to intensive research on their mechanical properties. This loosely defined group, the refractory metals, is comprised of those metals with high melting points in Groups IV, V, and VI of the Periodic Table; specifically the following: Metal Melting Point Niobium 2415°C Molybdenum 2650°C Tantalum 3000°C Tungsten 3400°C Since these metals are a l l body-centered-cubic transition metals, their mechanical properties exhibit those basic characteristics which distinguish them from the face-centered-cubic metals. With decreasing temperature, for example, the tensile strength of the body-centered-cubic metals increases rapidly while the du c t i l i t y exhibits a transition from a ductile-to-brittle, or from ductile-to-less ductile type of behaviour. It appears that molybdenum and tungsten exhibit the transition from ductile-to-brittle behaviour, but that vanadium and niobium exhibit a ductile-to-less ductile transition. Another characteristic of this refractory group, which face-2 centered-cubic metals do not e x h i b i t , i s the strong i n f l u e n c e of i n t e r s t i t i a l l y d i s s o l v e d elements upon t h e i r mechanical proper-t i e s o This i n f l u e n c e i s shown i n the increase of t e n s i l e strength and i n the decrease of d u c t i l i t y w i t h i n c r e a s i n g i n t e r -s t i t i a l content. Before these r e f r a c t o r y metals may be used e f f i c i e n t l y i t i s necessary to examine and to understand f u l l y t h e i r t e n s i l e behaviour, but to do t h i s , much more data i s r e q u i r e d . In t h i s research p r o j e c t the r e s u l t s of a s e r i e s of t e n s i l e t e s t s were used to examine the mechanical p r o p e r t i e s of tantalum over a temperature range of 100°C to — 1 9 6°C, P a r t i c u l a r a t t e n t i o n was given to the e f f e c t of n i t r o g e n , oxygen, and hydrogen on these p r o p e r t i e s , Although i t has the advantages of a high melting point, a low vapour pressure, e x c e l l e n t d u c t i l i t y , and good high-temper-ature s t r e n g t h , tantalum, l i k e the other r e f r a c t o r y metals, has the disadvantage of being extremely r e a c t i v e at high temperat-ures. I t w i l l combine r e a d i l y with oxygen, hydrogen, n i t r o g e n , and the halogens i n both the s o l i d and the molten s t a t e s . An-n e a l i n g must be c a r r i e d out, t h e r e f o r e , i n e i t h e r a high vacuum or an atmosphere of a p u r i f i e d i n e r t gas. B. THEORY The phenomena of strong temperature dependence of the t e n s i l e p r o p e r t i e s , the s t r a i n r a t e s e n s i t i v i t y of the t e n s i l e p r o p e r t i e s , and the t r a n s i t i o n from a d u c t i l e - t o - b r i t t l e , or from d u c t i l e - t o - l e s s d u c t i l e type of f r a c t u r e i n body-centered-cubic metals have become an a c t i v e area f o r research i n themselves. •1 Wessel"'" has given an e x c e l l e n t summary of the t h i n k i n g up t o 1956, on the mechanisms p r e s e n t l y used to e x p l a i n these phenomena. A 1959 p u b l i c a t i o n edited by Overbach, Felbeck, Hahn, and Thomas covers the f i e l d i n more d e t a i l w i t h a t h e o r e t i c a l treatment . I . D u c t i l e - t o - B r i t t l e T r a n s i t i o n The g e n e r a l l y recognized concept of the d u c t i l e - t o -b r i t t l e t r a n s i t i o n s t a t e s that b r i t t l e f r a c t u r e s w i l l occur when the y i e l d - p o i n t s t r e s s exceeds the cleavage s t r e s s . This condi-t i o n appears to be reached by lowering the temperature, or by i n c r e a s i n g the s t r a i n r a t e , or by i n t r o d u c i n g a t r i a x i a l s t r e s s c o n d i t i o n w i t h the use of a notch. Notches cause b r i t t l e f a i l u r e because they increase the r a t i o of normal t o shear stress.-. The normal s t r e s s i s increased to a value greater than the cohesive strength of the m a t e r i a l , r e s u l t i n g i n a b r i t t l e f r a c t u r e . Wessel's"*- d e s c r i p t i o n of the d u c t i l e - t o - b r i t t l e t r a n s i -t i o n i s summarized herewith: The increased r e s i s t a n c e to i n i t i a l p l a s t i c flow w i t h decreasing temperature, e x h i b i t e d by the strong temperature dependence of y i e l d point s t r e s s , has been explained i n terms of the anchoring of d i s l o c a t i o n s by atmospheres of i m p u r i t i e s . This theory was developed by C o t t r e l l and B i l b y ^ and l a t e r elaborated by F i s h e r ^ . The C o t t r e l l - B i l b y Theory, as i t i s known, i s premised on the migration of so l u t e atoms to the s t r e s s f i e l d a s s o c i a t e d w i t h a d i s l o c a t i o n , where they r e l i e v e some of the s t r e s s , thereby lowering the energy of the system. The s o l u t e atoms form an atmosphere around the d i s l o c a t i o n s and exert an anchoring fo r c e p r o p o r t i o n a l to the energy decrease of the system, which occurred upon migration of the sol u t e atoms to the 4 stress f i e l d o Cottrell and Bilby^ postulated that, minor thermal fluctuations add- sufficient energy to the applied stress to effect the breaking away of a small dislocation loop, which then drags the remaining part of the dislocation from i t s atmosphere. The minimum amount of energy required for this process of nucle-ation was estimated by Cottrell and Bilby^ and found to be within reasonable limits,, C o t t r e l l ^ J 5 originally explained the breaking away of the f i r s t dislocation from i t s atmosphere as the beginning of the abrupt yield phenomenon. During subsequent nucleation and exten-sion of one or more loops, other dislocations break away result-ing in a catastrophic yielding. Since thermal fluctuations decrease with decreasing temperature, a greater stress is required to tear the dislocation from i t s atmosphere at low temperatures than at high temperatures; hence, the temperature dependence of yield point stress. This theory requires no pre-yield strain except that which results from the f i r s t few dislocation loops' breaking away from their atmospheres; but Clark^ and his associ-ates have given experimental evidence indicating the existence of considerable pre-yield strain. Clark's^ observations can be accounted for i f there are a large number of dislocations moving through the lat t i c e prior to abrupt yielding. An estimate of C o t t r e l l 7 s ^ indicates that approximately 1000 piled-up dislocations per grain are required in the case of mild steel tested at —196°C. He describes the dislocations as being "piled up" because he thinks that, after release, the dislocations move through the lattice until they pile up at barriers which are in the form of grain boundaries, sub-grain boundaries, i n c l u s i o n s , e t c . I t i s probable that some d i s l o c a t i o n s s t a r t to break away at a s t r e s s i n the v i c i n i t y of the e l a s t i c l i m i t , and as the s t r e s s increases the number of d i s l o c a t i o n s breaking away incr e a s e s , reaching a maximum at the y i e l d p o i n t stresso As a r e s u l t of the p i l i n g up of d i s l o c a t i o n s at b a r r i e r s and the i n c r e a s i n g s t r e s s l e v e l , high s t r e s s concentrations are developed i n regions i n the v i c i n i t y of the p i l e - u p s . These s t r e s s e s a c t i v a t e d i s l o c a t i o n sources i n the neighbourhood of the p i l e - u p s o As a r e s u l t the s t r e s s i n the region of the o r i g i n a l p i l e - u p s i s r e l a x e d . Reaching the c r i t i c a l s t r e s s necessary to a c t i v a t e nearby d i s l o c a t i o n sources and r e l a x i n g the s t r e s s i s termed the "breaking through" or "breaking away" of the piled-up d i s l o c a t i o n group from i t s b a r r i e r . These phenomena cause higher m i c r o s t r e s s e s in. neighbouring p i l e - u p s , t r i g g e r i n g a cataclysmic y i e l d i n g and an ass o c i a t e d drop i n load. At low temperatures, where b r i t t l e f r a c t u r e i s observed to occur during y i e l d i n g , the mechanism i s thought t o be d i f f e r -ent. Here the s t r e s s necessary to move a d i s l o c a t i o n or to a c t i v a t e a d i s l o c a t i o n source i s g r e a t l y increased, c r e a t i n g higher l o c a l i z e d m i c r o s t r e s s e s . When these s t r e s s e s exceed-the material's cohesive s t r e n g t h , microcracks may form i f the m a t e r i a l i s not favourably o r i e n t e d f o r s l i p . The formation of micro-cracks and p l a s t i c flow may, t h e r e f o r e , occur simultaneously. The i n i t i a t i o n of one or more microcracks, together w i t h some p l a s t i c flow, i s assumed to t r i g g e r the abrupt y i e l d i n g . During the a s s o c i a t e d drop i n load the microcracks grow i n number and i n 7 s i z e to propogate and terminate i n b r i t t l e f r a c t u r e . G r i f f i t h ' i n h i s c r i t e r i o n s t a t e s t h a t they must reach a c r i t i c a l s i z e before they propagate to cause b r i t t l e f a i l u r e . 6 2. Temperature Dependence of Y i e l d S t r e s s , Researchers have expended much time and e f f o r t i n attempts to d e r i v e a theory to express the temperature dependence of y i e l d s t r e n g t h of body-centered-cubic metals, Zener and Holloman developed an emperical r e l a t i o n s h i p to f i t t h e i r r e s u l t s on s t e e l which Bechtold'^ used to f i t h i s data on tungsten. I t s t a t e s that y i e l d s t r e s s , which i s taken as an o f f s e t s t r e s s , i s p r o p o r t i o n a l to the exponential (1/T), P l o t t i n g the l o g of the y i e l d s t r e s s versus the r e c i p r o c a l of absolute temperature should r e s u l t i n a s t r a i g h t l i n e . Zener and Holloman have a s s o c i a t e d w i t h t h i s equation an a c t i v a t i o n energy, which may be determined from the p l o t . To what process t h i s a c t i v a t i o n energy r e f e r s i s of much contention. In t h e i r work Zener and Holloman a r r i v e d at a value f o r s t e e l of 90 to 120 c a l o r i e s per gram mole. I t should be noted t h a t t h i s r e l a t i o n s h i p was meant to apply only to o f f s e t y i e l d s t r e s s e s , not to upper y i e l d p o i n t s t r e s s e s . There are, however, some cases^'^ i n which upper y i e l d point data does appear to support the r e l a t i o n s h i p . More r e c e n t l y F i s h e r ^ derived a r e l a t i o n s h i p , by e l a b o r a t i n g on the C o t t r e l l - B i l b y Theory^„ He suggests t h a t the product of y i e l d point s t r e s s and the absolute temperature i s a constant; i . e . on p l o t t i n g y i e l d s t r e s s versus the r e c i p r o c a l of the absolute temperature, a s t r a i g h t l i n e should r e s u l t i f the theory i s v a l i d . This r e l a t i o n s h i p was derived by expressing the r a t e of n u c l e a t i o n of d i s l o c a t i o n loops (described i n the C o t t r e l l - B i l b y Theory-^) as being p r o p o r t i o n a l to exponent (-W*/kT) ; where W* i s 7 the minimum, work, required to form a d i s l o c a t i o n loop of c r i t i c a l s i z e f o r break-away; k i s Boltzman's constant; and T i s the absolute temperature. The r a t e i s e s s e n t i a l l y zero u n t i l the s t r e s s i s s l i g h t l y below the y i e l d point s t r e s s , and then increases r a p i d l y a s . i t approaches t h i s p o i n t . I t i s assumed t h a t , w i t h a constant r a t e of s t r a i n i n g at any given temperature, the r a t e of nucleation. w i l l be constant at the y i e l d point s t r e s s . Therefore, exponent (-W*/kT), the r a t e of n u c l e a t i o n , i s a constant. By s u b s t i t u t i n g f o r W* and s i m p l i f y i n g , F i s h e r ^ a r r i v e d at the equation, ST/G^ = constant; where S i s the y i e l d p o i n t s t r e s s , T, the absolute temperature; and G, the shear modulus. The v a l i d i t y of t h i s theory has been e s t a b l i s h e d to some extent by data on iron^ 4 -, molybdenum^, and vanadium-^. The r e l a t i o n s h i p does not appear to hold below approximately 140°K. I t i s thought that below t h i s temperature n u c l e a t i o n of the d i s l o c a t i o n loop i s ho longer r e q u i r e d f o r y i e l d i n g , as at these temperatures the s t r e s s has reached a l e v e l high enough to t e a r the d i s l o c a t i o n away from i t s atmosphere. I I PREVIOUS WORK ON TANTALUM I n v e s t i g a t i o n s by Bechtold , Pugh , Schussler J , and Ingram"^ on the mechanical p r o p e r t i e s of tantalum i n the low temperature range of 100°C to —250°C revealed no d u c t i l e - t o -b r i t t l e t r a n s i t i o n . The y i e l d point s t r e s s and u l t i m a t e s t r e s s were found to increase continuously over the temperature range 100°C to «— 196°C, and the d u c t i l i t y d i d not appear to go through any sort of abrupt t r a n s i t i o n to l e s s d u c t i l i t y on decreasing the 15 temperature. B a r r e t t r e p o r t s that B a s i n s k i found t h a t even at o l8 4.2 K tantalum s t i l l e x h i b i t s some d u c t i l i t y . Schmidt r e p o r t s that Magnusson and Baldwin observed a s l i g h t embrittlement of annealed tantalum at low temperatures. However, a t r u e t r a n s i -t i o n was not apparent and the embrittlement was a t t r i b u t e d to hydrogen. The room temperature data f o r annealed tantalum i s given i n Table I . Ex c e p t i o n a l room temperature p r o p e r t i e s are evident from the r e d u c t i o n i n area and per cent elongation values given. The v a r i a t i o n i n t e n s i l e values appears to be due to v a r i a t i o n s i n p u r i t y of the m a t e r i a l . Table I I , page 10, shows the analyses of the m a t e r i a l s used by some of the i n v e s t i g a t o r s . Because of the var i a n c e i n the i n t e r s t i t i a l content and other v a r i a b l e s such as g r a i n s i z e , a comparison of the p r o p e r t i e s i s very d i f f i c u l t to make. The s e n s i t i v i t y of t e n s i l e p r o p e r t i e s and d u c t i l i t y to increases i n s t r a i n r a t e appears to be a matter of contention. Kattus* r e s u l t s show a s i g n i f i c a n t decrease i n d u c t i l i t y f o r a 17 corresponding change of 2000:1 i n s t r a i n r a t e , w h i l e t M i c h a e l ' s data i n d i c a t e s l i t t l e i f any e f f e c t . TABLE I ROOM TEMPERATURE DATA FOR ANNEALED TANTALUM Investigation Strain Rate in/in/min Yield Stress o Offset Proportional Limit psi. Ulto Stress x 10 J Percent Elongation Per Cent Reduction in Area Grain Diameter Bechtold 1 1 .018 - 39,300 ^9,800 h5 86 oOi+7 12 Pugh * 57,350 - 67,1^0 25o3 _ O088 Kattus 1 6 .003 32,700 5 M 0 0 - M+,600 61,800 ^6o3 3^c2 - -Michael 1 7 .018 lo2 - if 2 ,000 57,000 58,000 67 ,000 38,0 38,0 81+ 82 -Schussler1-^ Arc-Melted Electron-Beam Melted 0 O 0 5 .005 ,005 ,005 -37,000 27,800 11,900 9 ,000 53,800 51,100 30,200 28,800 -80 92 95 99 ,025 ,10 ,2 o5 Gebhardt 1 9 - - - 27,500 38,0 89 ' -Schmidt 2 0 - 26,300 29,^00 36oO - -v 21 Yancey 30-lf 0 , 0 0 0 ^0 -50 ,000 30-1+0 Fansteel 2 2 50,000 h0OQ - -23 Fansteel = - - 100,000 lloO - = Ingram1** - - - 35,000 — 95 Myres^ - - 33,500 50o0 10 TABLE II CHEMICAL ANALYSES OF TANTALUM Concentration parts per million 13 Schussler Bechtold1 1 Pugh 1 2 Electron Fansteel Fansteel Arc - beam Vacuum Vacuum Element Melted Melted Sintered Sintered C 150 50 100 200 °2 280 60 - 56 H 2 10 1 - -N 2 60 60 100 130 B 1 1 - -Cb 100 100 1000 Cr 100 100 - _ Cu 10 10 - -Fe 100 100 „ • - 150 Ni 100 100 _ — Si 50 50 - -Ti 100 100 - -W 56 56 - 100 V 30 30 -Zr 30 30 Heat Treatment of above Materials Annealing Temp. ' Time Vacuum Grain Size ASTM Material Texture Schussler 130*f°C 1 hour ,025 mm, 8 swaged bar 1350°C* : l l ^ C * 1 hour 1 hour 1 hour d o mm. • h swaged bar 0 2 mm. 2 swaged bar o 5 mm. 0 swaged bar 1700 C* 1 hour 5 x K f ^ mm. of Hg oOh-7 -mm. 5-6 swaged bar X 1 hour „088 mm.. 6-7 sheet 111 112 13 13 Arc- Melted Material it f Schussler Electron-beam Melted Material Bechtold 1 1 Fansteel Vacuum-Sintered Material 12 * Pugh Fansteel Vacuum-Sintered Material Some data on the temperature dependence of the modulus of e l a s t i c i t y have been gathered, but they do not extend below room temperature„ The e f f e c t s of temperature on the u l t i m a t e t e n s i l e s t r e n g t h , y i e l d point s t r e s s , and d u c t i l i t y are shown i n Figures 1 and 2. The r e s u l t s of B e c h t o l d 1 1 , Pugh 1 2, K a t t u s 1 6 , and the r e s u l t s f o r S c h u s s l e r ' s 1 ^ arc-melted m a t e r i a l agree quite w e l l . The curve f o r Bechtold's data l i e s s l i g h t l y below that of Pugh, but Pugh's data i s f o r 0.2 per cent o f f s e t s t r e s s , whereas Bechtold's data i s f o r the p r o p o r t i o n a l l i m i t . Under these curves l i e the curves f o r both the arc-melted and the electron-beam melted m a t e r i a l , the l a t t e r being c o n s i d e r a b l y more pure. The only apparent d i f f e r e n c e between these.materials i s t h e i r r e l a -t i v e i n t e r s t i t i a l contents,which appear 'to govern the r e l a t i v e p o s i t i o n s of the d i f f e r e n t m a t e r i a l s on the y i e l d p o i n t s t r e s s a x i s . Above 100°C an anomalous increase i n u l t i m a t e s t r e s s appeared i n the data of Pugh 1^, S c h u s s l e r 1 ^ , and B e c h t o l d 1 1 . Pugh a t t r i b u t e d the increase to s t r a i n aging e f f e c t s . The percent elongation data shown i n Figure 1 gives more evidence of the e f f e c t of i n t e r s t i t i a l content on mechanical p r o p e r t i e s , the purest m a t e r i a l showing the highest room temper-ature e l o n g a t i o n , and the l e a s t pure e x h i b i t i n g the lowest. There are two peaks i n B e c h t o l d ' s 1 1 data which a l s o appear i n 12 Pugh's , but at a higher temperature. Pugh a s c r i b e s the peaks to i n t e r a c t i o n s between d i s l o c a t i o n s and d i f f e r e n t species of i n t e r s t i t i a l s . The r e d u c t i o n - i n - a r e a data given i n Figure 2 i n d i c a t e s very s t r o n g l y that a d u c t i l e - t o - b r i t t l e t r a n s i t i o n does not e x i s t 12 o| , -160 , -120 , -80 , -yo i p ,, ho , 8p nl i i i i i i i i , i i 1 1 1 1 L »200 -160 -120 -80 . -IfO 0 hO 80 Temperature C Figure 1. Yield Stress and Elongation of Tantalum 160 13 Temperature °C 100 CO OJ Temperature C Figure 2. Ultimate Stress and Reduction in Area 14 i n the temperature range covered, and tha t there i s very l i t t l e e f f e c t of s t r a i n , r a t e on t h i s property. There i s very l i t t l e i nformation a v a i l a b l e r egarding the e f f e c t of absorbed gases on the mechanical p r o p e r t i e s of tantalum.' I t appears that the greatest p o r t i o n of e x i s t i n g data deals w i t h the v a r i a t i o n of hardness w i t h gas content, the most 25 recent data' being that of P e r k i n T s group of i n v e s t i g a t o r s . 26 •Table I I I shows the e f f e c t of va r i o u s gases on the room temper-ature e l o n g a t i o n of tantalum. TABLE I I I EFFECT OF VARIOUS GASES ON TANTALUM AT ELEVATED TEMPERATURES Gas Hydrogen Nitrogen A i r Oxygen Temp. °C 100 200 250 300 350 400 400 400 300 400 350 350 Duration of Test - Hours 2 5 y 5 5 1 2 3 5 1 5 5 G;ain i n Weight Percent 0.000 0.000 0.000 0.000 0 .0073 0.01L. 0.013 0.031 0.0000 0.0053 0.013 0.011. Room Temperature Elongation Percent i n 1 i n . 31 ( o r i g i n a l ) 31 33 32.8 32.8 30.6 25.8 16 . 0 some embrittlement 31 ( o r i g i n a l ) 28.2 22 . 0 33.2 ( o r i g i n a l ) 27.1 33.2 ( o r i g i n a l ) 26.6 A c THE EFFECT OF HYDROGEN M i l l e r ^ r e p o r t s that t h e hardness of tantalum increases p r o g r e s s i v e l y and that t h e strength and d u c t i l i t y decrease w i t h i n c r e a s i n g a d d i t i o n s of hydrogen,, He r e p o r t s , however, that the data are not a v a i l a b l e . Figure 3 ( a f t e r Perkin's J) gives t h e increase i n hardness w i t h i n c r e a s i n g hydrogen content. The curve shows a steady r i s e up to a Diamond Hardness Number of 170 co r r e -sponding to a hydrogen content of 16 atomic per cent. Bakish-^ r e p o r t s that hydrogen i n tantalum leads to a b r i t t l e type of f r a c t u r e on bending at room temperature. Seghezzi-^l found t h a t the presence of hydrogen a f f e c t e d the s t r e s s - s t r a i n curve and mechanical p r o p e r t i e s i n a manner s i m i l a r to that shown i n Figure 4, page 17, B. THE EFFECT OF NITROGEN Seghezzi-^ s t u d i e d the r e a c t i o n of nit r o g e n w i t h tantalum. Figure 4, page 17, shows the v a r i a t i o n of hardness, elongation,_and t e n s i l e s t r e n g t h w i t h i n c r e a s i n g n i t r o g e n content. Figure 5, page 17, shows the shape of the t e n s i l e curves t h a t Seghezzi obtained. He reported f i n d i n g a very small y i e l d point f o r degassed m a t e r i a l w h i l e those of low n i t r o g e n content showed a d i s t i n c t upper and lower y i e l d point w i t h a w e l l - d e f i n e d p l a s t i c r e g i o n . The samples w i t h high n i t r o g e n content were found to exhibit, a f a l l i n g - a w a y of the load a f t e r y i e l d i n g , u n t i l the specimen broke i n a b r i t t l e manner. Perkins ' a l s o showed that n i t r o g e n increased the hardness of tantalum but at a much f a s t e r r a t e than hydrogen (see Figure 3). 30 Bakism found that a high, n i t r o g e n content e m b r i t t l e d 16 h 6 8 Atomic % Gas Figure 3<, Hardening of Tantalum by Gases, 17 a a M £ -P UO C 0) M •P CO -P • H o T3 rH CD •H 150 ^  125 H 100 75 50 25 0 Yield Strength 60 50 ho 30 20 10 0 o •H -P CO $0 c o H •p a cu M a> . 1 2 3 ^ Atomic % Nitrogen Figure h. Mechanical Properties of Tantalum containing Nitrogen w w CD -P CO 0.0 Atomic # N 2.6 Atomic % N Strain Figure 5. Effect of Nitrogen on the Stress-Strain Curves of Tantalum. tantalum and that the embrittlement can be i d e n t i f i e d w i t h the p r e c i p i t a t i o n of a second phase, TaN, on the {lOO} plane. C o THE EFFECT OF OXYGEN 2 8 M i l l e r reported that t e n s i l e s t r e n g t h , elongation, and r e d u c t i o n i n area of tantalum a l l vary w i t h oxygen content a s shown i n Figure 6 ( a f t e r Gebhardt and Seghezzi). The modulus of e l a s t i c i t y , shown i n Figure 7 was a l s o r e p o r t e d 2 ^ to be a f f e c t e d by oxygen content. 100 80 60 40 20 0 0.4 0.8 1.2 1.6 2 Atomic % Oxygen Figure 6. Dependence of Mechanical P r o p e r t i e s of Tantalum on the Oxygen Content. s s W ) O CO -p ° H CD ttD - P f-i CO <u CD . b O U d - P o • H CO r H CD o r H ° H • P W O a CD E n CD l.o i„5 Atomic $ Oxygen Fi g u r e 7. Dependence of the E l a s t i c Modulus on the Oxygen Content. Gebhardt^ found that hardness increased w i t h oxygen content. His r e s u l t s agree q u i t e w e l l w i t h those of Perkins J , whose r e s u l t s are shown i n Figure 3j page 1 6 , Bakish-^ reported that oxygen a d d i t i o n s above the s o l u b i l i t y l i m i t w i l l cause tantalum to become very b r i t t l e , D„ THE EFFECT OF AIR P e r k i n s ^ observed that the e f f e c t of a i r a d d i t i o n s on the hardness was s i m i l a r to the e f f e c t s caused by a d d i t i o n s of oxygen and ni t r o g e n i n an a d d i t i v e manner. This phenomenon i s shown i n Figure 3 , page 1 6 , I l l EXPERIMENTAL 20 A o MATERIALS The tantalum used i n t h i s investigation was supplied by Murex Limited of Rainham, England and by the Wah Chang Corporation of Albany, Oregon, two l o t s of material being supplied by each company. The analysis of each i s shown in Table IV, The material supplied by Murex, designated in t h i s thesis as l o t 1M and l o t 2M, was vacuum sintered. The electron-beam melted material received from Wah Chang i s designated as l o t 1 W C and l o t 2 W C , B. SPECIMEN PREPARATION 1, Lot 1M Lot 1 M was supplied in the form of an annealed s t r i p 1 inch x 1 2 inches x ,060 inches in size. This s t r i p was cold r o l l e d i n a number of steps to a thickness of , 0 1 5 inches then cut into s t r i p s 0 , 5 inches x 2 , 2 5 inches. The s t r i p was r o l l e d i n the d i r e c t i o n of the 1 2 inch measurement and the 2 , 2 5 inch dimension was taken in the d i r e c t i o n of r o l l i n g . The s t r i p s were then chemically polished f o r approximately f i v e seconds i n a solution of f i v e parts sulphuric acid, two parts n i t r i c acid, and two parts hydrofluoric acid. The procedure removed a l l scratches, the oxide layer, and any d i r t that might have caused contamina-tion during the annealing operation that followed, A series of hardness measurements were taken before and afte r the chemical poli s h i n g to see i f there was any hydrogen absorption. It was found that none took place, because the hardness measurements remained consistent, A subsequent analysis supported t h i s f a c t . A l l hardness measurements taken i n t h i s investigation were made 21 TABLE IV CHEMICAL ANALYSIS OF TANTALUM Concentrations(parts per m i l l i o n ) O r i g i n a l Ingot of Lot Lot Lot Lot lWCk Lot Lot Lot Lot Element IM* IM* 2M* Lot 2WC 1WC? 1WC# 2WC^ 2WC c 50 31 177 <30 47 n o 35 30 °2 20 232 487 <50 120 < 50 170 . n o No 100 162 84 20 17 65 30 75 4 2 11 3.8 2 1.6 2.6 2.2 3 <"20 B < 1 Cb <500 Cd <50 < 5 Cr <20 Cu 20r < 40 Fe 350 150* <fl00 K <20 Mg <20 Mn < 20 Mo 1800 100* <20 Na < 20 N i <100 50*- <20 Pb < 20 Sn 100* •" < 20 S i <100 T i 100 50*" «150 V *100* < 20 W 700 <300 Zn < 20 Zr <500 - A n a l y s i s done by Murex Limited - A n a l y s i s done by The Wah Chang Corporation ~¥ - A n a l y s i s done by Ledoux and Company 22 w i t h a Tukon Micro-hardness Tester using a 1 3 6 ° diamond indentor. These s t r i p s were then annealed i n a zone r e f i n e r described elsewhere-^, p 0 r t h i s operation a tantalum specimen holder was designed to hold t w e n t y - f i v e to t h i r t y specimens w i t h i n the loop of a long filament as shown i n Figure $„ Molybdenum wire was used to make extensions f o r the f i l a m e n t so as to place i t adjacent only to the holder. A platinum, 10% rhodium/platinum, thermocouple was i n s e r t e d i n t o the stack of specimens to a l l o w f o r temperature measurements. This thermo-couple was brought out through soldered connections i n the top of the zone r e f i n e r and m i l l i v o l t s were read on a Fye potentiometer. Figure 8 Specimen Holder and Filament i n Zone R e f i n e r . 2 3 approximately 1350°C i n a vacuum of l e s s than 5 x IO -- 3 mm. of Hg f o r one hour. I t was very d i f f i c u l t to maintain a constant temperature f o r t h i s length of time and to reproduce the same co n d i t i o n s f o r each of the batches. The average r e c r y s t a l l i z e d g r a i n s i z e that r e s u l t e d , v a r i e d from 30.4 to 49«3 grains per mm. (ASTM 7 to 8), and the average Diamond Pyramid Hardness Number v a r i e d from 133°3 to 144°5« The range of g r a i n s i z e was 26 to $6 g r a i n s per mm. (ASTM 7 to 9), and the range of hard-ness was 121 to 158. This l a r g e range i s thought to be due to a heat gradient between the center and the outside of the stack of specimens i n the holder, and, to the c l o s e s t a c k i n g of the s t r i p s , which may have decreased the e f f i c i e n c y of degassing. A number of s t r i p s from t h i s l o t were then cold r o l l e d f u r t h e r to give reductions i n area of 10%, 25%, 40%, and 50%. These s t r i p s were then cut to specimen shape, the dimensions of which are shown i n Figure 9, and a hardened s t e e l j i g was used to shape the specimens. The specimens were then p o l i s h e d mechanically w i t h various grades of emery paper down to 000 grade. This procedure was followed by chemical p o l i s h i n g as described e a r l i e r . F i gure 9» Dimensions of the T e n s i l e Specimen 2 4 A g i n g was t h e n c o n d u c t e d a t t e m p e r a t u r e s o f 700°C, 40G°C, and 300°C f o r one h o u r i n a v a c u u m - a n n e a l i n g f u r n a c e d e s c r i b e d e l s e w h e r e ^ , The r e m a i n i n g a n n e a l e d s t r i p s were shaped t o s p e c i m e n s i z e by f i r s t m i l l i n g t o a p p r o x i m a t e s i z e , t h e n by f i l i n g i n t h e h a r d e n e d s t e e l j i g , and f i n a l l y by p o l i s h i n g as d e s c r i b e d e a r l i e r . A h a r d n e s s t r a v e r s e was t a k e n t o c h e c k t h a t a l l e f f e c t s o f s h a p i n g t h e s p e c i m e n s were removed by f i n i s h i n g and p o l i s h i n g . A l l s u c h e f f e c t s had been r e m o v e d . 2 . L o t 2M L o t 2M came i n t h e same f o r m as l o t 1M and was a l s o r o l l e d down t o .015 i n c h e s t h i c k and c u t i n t o s t r i p s as b e f o r e . F o r t h i s l o t a p u n c h and d i e ( s e e F i g u r e 10) was employed t o o b t a i n a u n i f o r m s p e c i m e n . The s p e c i m e n s were c h e m i c a l l y p o l i s h e d as b e f o r e . As l o t 2¥x was more p u r e t h a n l o t I K ( s e e T a b l e I V , page 21 ) , t h e v a c u u m - a n n e a l i n g f u r n a c e m e n t i o n e d e a r l i e r was e m p l o y e d . Three s p e c i m e n s were l a i d i n a molybdenum b o a t and i n s e r t e d i n t h e f u r n a c e t u b e , and a n n e a l i n g was c o n d u c t e d a t 1100°C i n a vacuum o f l e s s t h a n 1 x 10~5 mm. o f Hg f o r t w e n t y -f o u r h o u r s . When a h a r d n e s s t r a v e r s e was made i t was f o u n d t h a t a n n e a l i n g had t a k e n p l a c e o n l y on t h e s i d e away f r o m t h e molybdenum b o a t , w h i l e t h e s i d e f a c i n g t h e b o a t was s t i l l i n t h e work h a r d e n e d c o n d i t i o n . I t was t h o u g h t t h a t a n n e a l i n g f a i l e d t o t a k e p l a c e t h r o u g h o u t t h e sample b e c a u s e a t e m p e r -a t u r e g r a d i e n t e x i s t e d f r o m one s i d e o f t h e s p e c i m e n t o t h e o t h e r . 2 5 Figure 11. Modified Sintering Furnace showing Vacuum System 26 Because of t h i s - e f f e c t and the small c a p a c i t y of the furnace, t h i s method of annealing was abandoned. Instead a s i n t e r i n g furnace manufactured by Pereny Equipment Company was modified as shown i n Figure 11. A fo u r foot piece of 1 5/8 inch Oo Do 316 s t a i n l e s s s t e e l water pipe with one end welded closed was i n s e r t e d i n t o the tube of the furnace w i t h the open end pro-t r u d i n g through a rubber bung i n the opening of the furnace. To the open end was f i t t e d an Edward's mercury d i f f u s i o n pump. The s e a l between the pipe and the elbow was made by rubber "0" r i n g s . This end of the pipe was kept c o o l by a water j a c k e t . The tem-perature was measured by a tungsten, 26% rhenium/tungsten, thermocouple and the voltage was read on a Pye potentiometer. The molybdenum windings of the furnace were protected by a continuous flow of hydrogen. Because, above 1000°C, i t was found th a t the hydrogen d i f f u s e d r a p i d l y through the s t a i n l e s s s t e e l pipe, the atmosphere i n the furnace was changed to argon. With argon, a vacuum of l e s s than 5 x 10"^ was obtained above 1000°C, whereas p r e v i o u s l y at that temperature a vacuum of only approxi-_3 mately 9 x 10 was p o s s i b l e . A t r i a l run i n t h i s modified annealing furnace revealed that the vapour pressure of the s t a i n l e s s s t e e l at 1300°C was too high, r e s u l t i n g i n a co a t i n g ( c o n t a i n i n g considerable amounts of n i c k e l , chromium., and iron) on the tantalum specimens. In an e f f o r t to combat t h i s problem a v i t r e o s i l tube was sealed at one end and placed i n the s t a i n l e s s s t e e l tube, so that the open end of the tube was s i t u a t e d i n the cooled s e c t i o n of the furnace. A t r i a l run using t h i s arrangement appeared to be s u c c e s s f u l , even though annealing had not taken p l a c e . This f a i l u r e to anneal was thought to be due to i n s u f f i c i e n t temperature. The e n t i r e batch was then put i n molybdenum boats, s t a c k i n g them so as to leave a space between the gauge length of each i n d i v i d u a l specimen. The boats were put i n t o tubes i n the furnace and annealing was c a r r i e d out at 13 50°C f o r f o r t y hours i n a vacuum of 4 x 10"^ mm. of Hg. During t h i s time the specimens became contaminated. The m a t e r i a l had r e c r y s t a l l i z e d , but the hardness was high, the average Diamond Pyramid Hardness Number being 220. The average number of grains per mm. was 55° 5 (ASTM 9)» A spectographic a n a l y s i s conducted i n Vancouver by the f i r m , Coast Testing, d i d not detect the presence of s i l i c o n . On examining thermochemical data the r e a c t i o n s 2Si0 2Si0+ 0^ and 2 2 2Si0-*~2Si + 0 were found to be p o s s i b l e . An a n a l y s i s done by Ledoux and Company of Teaneck, New Jersey revealed a high oxygen content, (see Table V, page 3D The contaminated specimens were che m i c a l l y p o l i s h e d to remove the l a y e r of oxide. Then a hardness t r a v e r s e was done on the cross s e c t i o n of a mounted specimen to check f o r any gradients of oxygen. There was no evidence of a gradient. 3. Lots 1WC and 2WC The m a t e r i a l from the Wah Chang Corporation came i n the form of a sheet 10 inches x 2 9 inches x .015 inches, f .Prom'.this sheet, 100 specimens were prepared by using the punch and die as was done f o r l o t 2M. This m a t e r i a l was ordered as. an annealed sheet, but i t was soon discovered that i t was s t i l l i n the work hardened c o n d i t i o n , so the cut specimens and the remaining part of sheet were returned f o r annealing. I t was found that a f t e r annealing, the cut specimens had a lower Diamond Pyramid Hardness Number (82) than the 28 remaining part of the sheet (104.5). The d i f f e r e n c e s i n g r a i n s i z e account to some extent f o r the d i f f e r e n c e s i n hardness as the cut specimens had on average of 20 grains per mm. (ASTM 6), w h i l e the sheet had an average- of 16 grains per mm. (ASTM 5). The d i f f e r e n c e i n i n t e r s t i t i a l content of the two also accounts f o r the d i f f e r e n c e s i n hardness, (see Table V, page 3D. C. GAS ADDITIONS The vacuum-annealing furnace p r e v i o u s l y mentioned was modified, as shown i n Figure 12, by the a d d i t i o n of a standard volume w i t h a mercury manometer and a metering volume of 9«975 c c . They were added i n the p o s i t i o n shown i n Figure 12 to all o w the d i f f u s i o n pump and co l d t r a p to be i s o l a t e d from the furnace tube and the volume, to al l o w evacuation of the system before the i n t r o d u c t i o n of the d e s i r e d gas, and to a i d i n a speedy 3h.tr.oduction and removal of the gas. The procedure f o l l o w e d was to place the specimens i n a molybdenum boat, which almost enclosed them. The specimens were stacked so t h a t t h e i r ends would overlap, thereby l e a v i n g a gap between the i n d i v i d u a l gauge lengths of the specimens. The boat c o n t a i n i n g the specimens was i n s e r t e d i n t o the furnace tube and the system was evacuated to l e s s than 5 x 10"^ mm. of Hg. The d i f f u s i o n pump and c o l d t r a p were then i s o l a t e d and the gas permitted to pass through a l i q u i d n i t r o g e n t r a p i n t o the furnace and the 4 - l i t e r volume. The gas was introduced u n t i l the pressure i n the volume reached s l i g h t l y l e s s than atmospheric pressure, approximately 687 mm. of mercury. At t h i s pressure the valves to the standard volume were closed and the system was once again evacuated to l e s s than 1 x 10 mm. of Hg. When t h i s 29 vacuum was a t t a i n e d the furnace was slowly heated to the desired temperature. The r a t e of heating to temperature was governed so as to keep the vacuum l e s s than 1 x 10"^ mm. of Hg at a l l times. At temperature, w i t h the vacuum l e s s than 5 x 10~5 mm. of Hg, the d i f f u s i o n pump and cold t r a p were once again i s o l a t e d and the gas allowed to enter the furnace tube. Figure 12. Modified Vacuum Annealing Furnace, showing Manometer and the 4 - l i t e r Volume. A f t e r v a rious t r i a l runs i t was found that i t was advantageous to a l l o w the pressure between the 4 - l i t e r volume and the furnace tube to equalize r a t h e r than to introduce only a set amount of gas. Using t h i s modified procedure i t was found that 30 the amount absorbed could be c o n t r o l l e d by the temperature, h o l d i n g the time constant at one hour. Nitrogen a d d i t i o n s were c a r r i e d out using temperatures of 800°C, 850°C, 9Q0°C, and 1000 oC. Oxygen and hydrogen were added at 500°C. A f t e r p e r m i t t i n g the specimens to soak i n the c o n t r o l l e d atmosphere at t h i s tempera-t u r e f o r one hour, the system was again evacuated. When the vacuum became l e s s than 1 x 10~5 mm. of Hg, the temperature was r a i s e d to 1100°C f o r a homogenization treatment of eighteen hours. During t h i s time the vacuum increased u n t i l , at the end of the treatment, i t was l e s s than 2 x 10"^ mm. of Hg. The hydrogen a d d i t i o n was an exception to t h i s procedure, as the specimens were soaked i n the hydrogen f o r three hours at 500°C, and then the system was evacuated and immediately cooled to guard against any degassing of the specimens, since tantalum may be degassed of hydrogen i n a vacuum at 1000°C . The specimens were cooled q u i t e r a p i d l y and then removed f o r hardness t e s t i n g . A t r a v e r s e of hardness was done to ensure that the absorption of gas had been uniform; very good r e s u l t s were obtained on sample specimens from each batch. The r e s u l t s of analyses done by Ledoux and Company and by the Wah Chang Corporation of the specimens which contained the various gas a d d i t i o n s are shown i n Tables V and VI, r e s p e c t i v e l y . The average Diamond Pyramid Hardness Numbers are a l s o shown i n Table V. 31 TABLE V ANALYSIS OF TANTALUM BY LEDOUX AND COMPANY Concentration (parts per m i l l i o n ) Average Treatment Lot Batch Tempo Hours 1WC 1 1000°C 1 2WC 2 1000°C 1/2 2WC 3 800°C 1/2 2WC 4 800°c 1/2 2WC 5 900°C 1/2 2WC 6 800°C 1 2WC 7 850TC 1 2WC 8 500° C 1 2WC 9 500°C 3 2M - contaminated D.P.H. C 0 N H No. 42 130 487 3.1 241 30 190 488 3.4 249 - 200 80 _ 132 - - 90 • - 128 - - 350 - 225 - - 130 - 148 - - 190 - 165 70 1090 20 - 448 - - - 299 126 177 487 84 3.8 220 TABLE VI ANALYSIS OF TANTALUM BY WAH CHANG CORPORATION Concentration (parts per m i l l i o n ) Lot Batch c 0 N H 1WC 1 - - NA -2WC 2 - - -2WC 3 - - NA -2WC 4 - - 75 -2WC ' 5 - - 330 -2WC 6 - - NA -2WC 7 - - 230 -2WC 2WC 8 9 < 30 840 -100 79 150 ) D. TESTING PROCEDURE A l l specimens were t e s t e d i n te n s i o n using an Instron T e n s i l e Tester which a u t o g r a p h i c a l l y recorded the load - e l o n g a t i o n curve of each specimen. The crosshead speeds used f o r t e s t s on Lot IM were . 0 5 and 2 0 inches per minute; those on l o t s 2M and 1WC, . 0 2 and 2 inches per minute; those on l o t 2WC, . 0 2 inches per minute. For l o t s IM and 2M, elongation of the gauge len g t h was measured d i r e c t l y from the gauge marks on each specimen; y i e l d s t r e s s values were c a l c u l a t e d by us i n g the load values taken from the autographic recorder and the measured area. Per cent elonga-t i o n data f o r l o t s 1WC and 2WC were c a l c u l a t e d from the loa d -elongation curve p l o t t e d by the autographic recorder. A m o d i f i c a t i o n of the Instron T e n s i l e Tester-^ employ-in g the s p e c i a l f i l e - f a c e d g r i p s - ^ was used f o r these t e s t s . The arrangement of g r i p s and u n i v e r s a l j o i n t s used i n the m o d i f i -c a t i o n i s shown i n Figure 1 3 . The low temperature t e s t s were conducted i n a petroleum ether ( 3 0 - 6 0 t e c h n i c a l grade) constant-temperature bath contained i n a wide-mouth dewar f l a s k , which f i t t e d over the assembly shown i n Figure 1 3 . The bath was cooled by means of a small e x t e r n a l l y — f e d l i q u i d n i t r o g e n c o n t a i n e r (see Figure 1 4 ) and s t i r r e d continuously by an e l e c t r i c — d r i v e n s t i r r e r . The use of the l i q u i d - n i t r o g e n cooled petroleum ether bath covered the range of temperature between 0°C and — 1 4 0 ° C i n c l u s i v e . The t e s t s at — 1 9 6 ° C were conducted by immersing the assembly i n l i q u i d n i t r o g e n ; those at —183°C,in l i q u i d oxygen. The temperature of o — 1 7 5 C was obtained by f i r s t c o o l i n g the apparatus and specimen to-19_6°C and,tiien by a l l o w i n g them to heat up to — 1 7 5 ° C . Figure 13. The M o d i f i c a t i o n of Instron T e n s i l e Tester Figure 14. Dewar Flask w i t h L i q u i d Nitrogen Container 34 The t e s t s above room temperature were c a r r i e d out i n a constant-temperature s i l i c o n e o i l bath heated by an immersion heater and s t i r r e d c ontinuously. I t was found that the bath took a very short time to reach a s t a t e of e q u i l i b r i u m and that the temperature remained e s s e n t i a l l y constant f o r the dur a t i o n of the t e s t . The temperature was measured by means of a copper, con-stantan thermocouple hooked around the specimen's edge. The e,m.f, of the thermocouple was measured on a Pye potentiometer of 10 m i c r o v o l t s s e n s i t i v i t y . IV EXPERIMENTAL RESULTS AND OBSERVATIONS 35 The r e s u l t s o b t a i n e d f r o m t e n s i l e t e s t i n g t h e d i f f e r e n t l o t s o f t a n t a l u m a t t e m p e r a t u r e s r a n g i n g f r o m 100°C t o —196°C a r e t a b u l a t e d i n A p p e n d i c e s I t o V I I I „ T h i s d a t a i n c l u d e s t h e u p p e r y i e l d p o i n t s t r e s s , t h e u l t i m a t e s t r e s s b a s e d on t h e o r i g i n a l c r o s s - s e c t i o n a l a r e a , and t h e p e r c e n t e l o n g a t i o n based on a u n i f o r m l y e l o n g a t e d gauge l e n g t h o f 0,75 i n c h e s . A l l r e s u l t s d e m o n s t r a t e d t h a t m e c h a n i c a l p r o p e r t i e s depend s t r o n g l y on t e m p e r a t u r e and on t h e amount o f i n t e r s t i t i a l s o l u t e e l e m e n t s . T y p i c a l l o a d - e l o n g a t i o n c u r v e s f o r t h e v a r i o u s l o t s o f t a n t a l u m a r e shown i n F i g u r e 15. The c u r v e f o r m s v a r y as shown: some have a p a r t i c u l a r l y w e l l d e f i n e d u p p e r and l o w e r y i e l d p o i n t , , w h i l e o t h e r s have o n l y a v e r y s m a l l y i e l d p o i n t phenomenon, and some have none a t a l l . A , RESULTS OF I N I T I A L LOTS OF TANTALUM 1. L o t 1M ( a n n e a l e d Murex T a n t a l u m ) The r e s u l t s a r e g i v e n i n F i g u r e l6qand t a b u l a t e d i n A p p e n d i x A . T e s t s were c o n d u c t e d a t t e m p e r a t u r e s r a n g i n g f r o m 22°C t o —196°C a t s t r a i n r a t e s o f 0.067 and 26,7 i n . / i n . / m i n . O n l y t h e p e r c e n t e l o n g a t i o n v a l u e s a r e shown f o r t h e t e s t done a t t h e h i g h e r s t r a i n r a t e , as i t i s i m p o s s i b l e f o r t h e a u t o -g r a p h i c r e c o r d e r t o o p e r a t e a t t h i s l e v e l . The e l o n g a t i o n v a l u e s f o r b o t h s t r a i n r a t e s were c a l c u l a t e d by u s i n g a d i r e c t m e a s u r e -ment o f t h e e l o n g a t e d gauge l e n g t h . The y i e l d p o i n t s t r e s s i s shown t o i n c r e a s e f r o m 47,000 p s i , a t ropm t e m p e r a t u r e t o 132,000 p s i . a t — 1 9 6 ° C . The p l o t o f e l o n g a t i o n v e r s u s t e m p e r a t u r e , shown i n F i g u r e 16, 36 S t r a i n S t r a i n •Figure 15. T y p i c a l Load-Elongation Curve?;.. 196°C Strain Strain Figure 15. (continued) Typical Load-Elongation Curves. 1 3 4 i2d 38 10 a. ro O I—I 110] X CO CO CD rH -p CO 1004 9 q S 80] CD =H r*"l n 70] CD Cu P . 604 504 i+0 =200 Temperature C 26,7 in/in/min. .067 in/ln/min. 4- 4-Temperature UC Figure 16. Properties versus Temperature for Tantalum Lot IM 80 39 e x h i b i t s the presence of a d u c t i l e - t o - l e s s - d u c t i l e t r a n s i t i o n o c c u r r i n g i n the range of —140°C to —180°C f o r the lower s t r a i n r a t e . The increase i n s t r a i n r a t e r a i s e s the t r a n s i t i o n temper-ature s i g n i f i c a n t l y , by 90°C, and accentuates t h i s t r a n s i t i o n , making i t more abrupt. The t y p i c a l load-elongation curves, given i n Figure 1 5 , i n d i c a t e that a l a r g e discontinuous y i e l d elongation takes place. On l o a d i n g a specimen at room temperature to the upper y i e l d p o i n t , i t was observed that a Luder's band appeared at each end of the gauge length at an angle of 4 5 ° to the length of the specimen. During the discontinuous elongation these bands enlarged, moving down the gauge length towards .each other. On meeting there was a s l i g h t drop i n the load followed by an increase due to work hardening. At low temperatures, y i e l d i n g occurred w i t h i n one of these Liider's bands at e i t h e r end of the gauge le n g t h . An example of t h i s can be seen i n Figure 1 7 . F i g u r e 17. S p ecimen s h o w i n g L u d e r ' s Band 40 Only a limited number of work-hardening and aging experiments were carried out. Since i t was decided that they did not really pertain to the problem, they were abandoned. For the sake of completeness, the results are tabulated in Appendix B. 2. Lot 2M (Contaminated Murex Tantalum) Plots of yield point stress and of per cent elongation versus temperature for this lot of tantalum are given in Figure 18 and the results are tabulated in Appendix C. The plot of yield point stress shows an increase from 70,000 to 155,000 psi., for the lower strain rate, and the higher strain, rate gives an increase from 80,000 to 160,000 psi. The scatter of results for this lot makes i t d i f f i c u l t to isolate the effect of strain rate, but there does appear to be a very definite increase in yield point stress with the increase in strain rate. The plot of per cent elongation versus temperature shows the transition from ductile-to-less-ductile behaviour for both strain rates. This transition appears to occur in the region between —100°C and —140°C for the lower strain rate and between —100°C and —120°C for the higher strain rate. Typical load-elongation curves in Figure 15, page 36, exhibit a variance in form, and the results for yield point stress showed a large scatter, thought to be due to non-uniform material resulting from contamination in the annealing furnace. Luder band behaviour similar to that in Lot IM was also observed. 42 3 o Lot 1WC (Pre-cut T e n s i l e Specimens from Wan Chang Corporation) The t e n s i l e t e s t r e s u l t s obtained f o r t h i s l o t of tantalum at temperatures ranging from 100°C to —196°C are com-p i l e d i n Appendix D. Two r a t e s of s t r a i n were used f o r these t e s t s ; o0267-and 2„67 in./in./min., P l o t s of y i e l d point s t r e s s and per cent elongation versus temperature are given i n Figure 19o The y i e l d point s t r e s s f o r the lower s t r a i n r a t e increases from 25,000 psi„ at 100°C to 111,000 p s i . at — 196°C. The elongation p l o t shows that a t r a n s i t i o n of d u c t i l e - t o - l e s s -d u c t i l e behaviour from 40 per cent elongation to l e s s than 1 per cent occurs at —80°C f o r the low s t r a i n r a t e , and at —2 0°C f o r the high s t r a i n r a t e . The expression " l e s s - d u c t i l e behaviour" i s -used i n t h i s case because, even at «—196°C, some reduction i n area occurred before f a i l u r e . T y p i c a l load-elongation curves i n Figure 15, page 36, show that below about —2 0°C a very sharp y i e l d point occurs, which i s considerably higher than the r e s t of the curve i n most cases. The s c a t t e r shown i n Figure 19 i s thought to be due to d i f f e r e n c e s i n accuracy of specimen alignment. There was no evidence of a prominent Luder's band at room temperature; r a t h e r the elongation seemed to take place u n i f o r m l y along the whole gauge le n g t h , but the specimen warped across the width (see Figure 2 0(a)). At low temperatures y i e l d i n g took place i n one very narrow Luder's band as shown i n Figure 20(c),page 44„ 4 . Lot 2WC (Wah Chang Sheet) The r e s u l t s of t e n s i l e t e s t s conducted at a s t r a i n r a t e of .0267 i n . / i n . / m i n . between 100°C and —196°C are contained i n ^3 12 Or \ - Strain Rate 2.67 in/in/min, © - Strain Rate .0267 in/in/min. X - Strain Rate 2.67 in/in/min, 0 - Strain Rate .0267 in/in/min, Temperature C 'Figure 19. Properties versus Temperature for Tantalum Lot 1WC 44 Appendix E„ P l o t s of y i e l d point s t r e s s and per cent elongation versus temperature are shown in Figure 21. The y i e l d point s t r e s s increased from 28,000 p s i . at 100°C to 12$,000 p s i . at —196°C. The elongation p l o t shows a gradual t r a n s i t i o n from 30 per cent elongation to l e s s than 1 per cent between —60°C and —196°C. The load-elongation curves and f a i l u r e behaviour were s i m i l a r to those of Lot 1WC. ( O J Cb) CO Figure 20. T y p i c a l Broken Specimens. I l l u s t r a t i n g from l e f t to r i g h t : f a i l u r e at room temperature, f a i l u r e at —60°C, and f a i l u r e at —196°C. B. RESULTS OF INITIAL LOTS OF TANTALUM 1. Nitrogen A d d i t i o n s The n i t r o g e n contents of the i n d i v i d u a l batches are shown i n Tables V and VI. Results of t e s t s on these batches conducted at a s t r a i n r a t e of .0267 in . / i n . / m i n . at temperatures 130 h5 30 -200 Temperature C Figure 21, Temperature "C Properties versus Temperature for Tantalum Lot 2WC 46 between 100°C and —196°C are ta b u l a t e d i n Appendix F. The plot of y i e l d point s t r e s s versus temperature i s presented i n Figure 22; the per cent elongation versus temperature plot, i n Figure 23, page 48. The y i e l d point s t r e s s values of Batches 3, 4, and 6, having an average of 100 pa r t s per m i l l i o n n i t r o g e n , a l l l i e on the same curve i n Figure 22. They e x h i b i t an increase from 40,000 p s i . at 100°C to 130,000 p s i . at —196°C. Batch 7, having 190 ppm. n i t r o g e n , shows an increase from 52,000 p s i . at 100°C to an estimated 150,000 p s i . at -—196°C. Batch 5, having 350 ppm. of n i t r o g e n , e x h i b i t s an increase from 70,000 p s i . at 100°C to 184,000 p s i . at —196°C, The r e s u l t s f o r Batches 1 and 2, having an average n i t r o g e n content of 488ppm., appear to l i e on a common curve showing an increase from 80,000 p s i . at 100°C to 204,000 p s i . at —196°C. The elongation values f o r Batches 1 and 2 do not l i e on a common curve, however (see Figure 23, page 4 8 ) , the elongation of Batch 1 i s l e s s than that of Batch 2. Both curves i n d i c a t e measurable d u c t i l i t y at —196°C Lot 1WC, Batch 1 shows 2 .5 per cent; while Lot 2WC, Batch 2 shows 9«5 per cent - elongation. Both values represent an increase over the elongation of the s t a r t i n g m a t e r i a l s . These d i f f e r e n c e s i n elongation are probably due to the d i f f e r e n c e s i n s t a r t i n g m a t e r i a l . The elongations f o r the other batches, which were from Lot 2WC, a l l e x h i b i t e d a decrease from approximately 20 per cent at 100°C feo. 10 per cent f o r Batch 5; 2 .5 per cent for Batches 3 , 4 , and 6; and an estimated 2 .5 per cent f o r Batch 7» a t —196°C. The loa d - e l o n g a t i o n curves and f r a c t u r e s were s i m i l a r to those of Lot lWC. No evidence of Luder's bands at 20°C was observed, 210, © - Batch 1 © - Batch 2 X - Batch 3 Batch h ® - Batch 5 Batch 6 Batch 7 -160 Temperature C Figure 22. Yield-Point Stress versus Temperature for Tantalum plus Nitrogen hQ •200 20 r a 10 o • H • P CO uo S 0 -20TJ ©-Batch 1 ©-Batch 2 -160 -120 •80 4 0 0 Batch 5 J 1 L J ' » I I I ' l 80 -® -p c 20 o CD a. 10 0 -160 -120 -80 -ho 0 hO Batch 7 J L -1. Temperature C Figur e 23. E l o n g a t i o n versus Temperature f o r Tantalum plus Nitrogen,, 80 but the f r a c t u r e , at low temperatures, occurred w i t h i n a narrow Luder's Band. 2. The Oxygen A d d i t i o n The m a t e r i a l w i t h an oxygen content of 1090 ppm. was t e s t e d at temperatures between 100°C and —196°C and at a s t r a i n r a t e of .0267 i n . / i n . / m i n . The r e s u l t s are tabulated i n Appendix G; the p l o t s of y i e l d p o i n t s t r e s s , and elongation versus temper-ature are presented i n Figure 24. The y i e l d point s t r e s s increases from 85,000 p s i . at 100°C to 200,000 p s i . at —196°C. The elongation e x h i b i t s a t r a n s i t i o n . f r o m 16 per cent to 5 per cent i n the region between —40°C and —9 0°C. The d u c t i l i t y at —196°C was greater than that of Lot 2WC, the s t a r t i n g m a t e r i a l . Some t y p i c a l load-elon-gation curves f o r t h i s m a t e r i a l w i t h a high oxygen content are shown i n Figure 15, page 36 . Many curves showed no y i e l d p o i n t . 3 . The Hydrogen A d d i t i o n Results of t e s t s conducted at a s t r a i n r a t e of .0267 i n . / i n . / m i n on m a t e r i a l contaminated with 200 ppm. hydrogen are t a b u l a t e d i n Appendix H and p l o t t e d i n Figure 25, page 51. The y i e l d point s t r e s s increased from 28,000 p s i . at 100°C to 134,000 p s i . at —196°C. The elongation decreased from 23 per cent at 100°C to 0 per cent ( i . e . b r i t t l e f a i l u r e ) at —60°C, which p r e v a i l e d to —107°C and then increased to 3 per cent at -—196°C. The t y p i c a l l o ad-elongation curves are shown i n Figure 15, page 3 6 . . The f a i l u r e s at —60°C, —80°C, and —107°C are b r i t t l e , but that at —196°C i s d e f i n i t e l y d u c t i l e . 50 J I I I I i I I i I I I I I L -160 -120 -80 -hO 0 hO 80 Temperature °C 30 o • H 0 I 1 1 1 i I i | i I I I I I I  - 2 0 0 -160 -120 - 8 0 -hO 0 hO 80 Temperature C Figu r e 2he Y i e l d P o i n t versus Temperature f o r Tantalum plus 1090 ppm. Oxygen. 51 130 120 -110 -•H100 to 90 h rn o H X m 80 to <D M - p oo 70 T5 H 0 •H >H I M CD S. 50 hO 60 30 -200 if or on 30. . •H - p CC bo o r H 20 " -P CD O JH 10.. CD 0 -200 -I--160 -120 -80 -hO 0 Temperature °C ho 8 0 ® Temperature Figure 2 5 . Yield-Point Stress and Elongation versus Temperature plus 299 ppm. Hydrogen. C o THE ACCURACY OF RESULTS The e r r o r i n r e s u l t s i s due to u n c e r t a i n t i e s i n measured values. The t o t a l p o s s i b l e e r r o r i s an accumulation of the u n c e r t a i n t i e s i n each measured qu a n t i t y . These i n d i v i d u a l u n c e r t a i n t i e s are discussed below, 1. The width of the gauge s e c t i o n was measured wi t h a micrometer capable of reading to .0001 inches, but the t h i c k n e s s of the specimens made measuring very d i f f i c u l t . The e r r o r i n t h i s measurement i s estimated to be - 0.000$ or 0.2$ per cent f o r a gauge leng t h width of 0.200 inches. The thickness was measured wi t h the same micrometer, the e r r o r i n measurement being e s t i -mated to be 0,0000$ or £ 0.033 per cent f o r a specimen t h i c k -ness of 0,01$ inches. The r e s u l t i n g e r r o r i n c r o s s - s e c t i o n a l area i s ±,283 per cent. 2. The load from the autographic recorded loa d - e l o n g a t i o n curve may be read w i t h an accuracy o f i 1/2 pound on the 200-pound f u l l s c a l e , and w i t h an accuracy o f ± 1 . $ pounds on the $00-pound f u l l s c a l e . For a l$0-pound load at the upper y i e l d p o i n t , the e r r o r would b e t 0,333 per cent, and f o r a 300-pound y i e l d point load the accuracy would be± 0 . $ per cent. The accuracy of the autographic r e c o r d i n g u n i t i s s t a t e d by the manufacturer-^ as being l e s s than 1 per cent of f u l l s c a l e , i f the time r e q u i r e d f o r the pen to t r a v e l the f u l l s c a l e i s more than f i v e seconds. A recorded point on a curve w i l l a l s o be w i t h i n t h i s accuracy i f i t l i e s on a curve whose slope at t h i s point i s such that more than f i v e seconds would be required f o r the pen to t r a v e l the f u l l s c a l e at t h i s slope. 53 The e r r o r using the 200-pound f u l l s c a l e , t h e r e f o r e , would be l e s s than i 2 pounds, and would be l e s s than i $ pounds i n the case of the 500-pound f u l l s c a l e . In the cases c i t e d above, the r e s p e c t i v e e r r o r s would be l e s s than ± 1.33 and ± 1 .66. The accuracy i n c a l c u l a t i n g upper y i e l d p o i n t s t r e s s i s c a l c u l a t e d to be, t h e r e f o r e , ± 1.95 per cent f o r the 150-pound load and±2 .44 per cent f o r the 300-pound load. 3 . To determine the per cent elongation f o r Lots 1M and 2M, a 0.75 inch gauge length was marked on the specimen. A f t e r t e s t i n g , the broken pieces were f i t t e d together and a measurement of the elongated gauge len g t h was made. The accuracy of both measurer ments i s estimated to be ± 0 .01 inches, and the e r r o r introduced on f i t t i n g the two pieces together i s estimated to be 0 .01 inches. When c o n s i d e r i n g , f o r example, a 0.75 inch gauge length that has elongated to 0.95 inches, the accuracy i s ± 1.33 per cent f o r the f i r s t measurement and ± 2 . 1 7 per cent f o r the second, r e s u l t i n g i n an o v e r a l l e r r o r of ± 3*50 per cent. In t h i s example the elongation was c a l c u l a t e d as being 26.7 per cent ± 3 . 5 0 per cent. The per cent elongation may, t h e r e f o r e , be expressed,as 26.7 £ 1.31 per cent. For the per cent elongation values of the remaining m a t e r i a l s , the r e s u l t s of Lots 1M and 2M were used i n conjunc-t i o n w i t h t h e i r a s s o c i a t e d load-elongation curves to p l o t a graph of rec o r d e r - c h a r t d i v i s i o n s from the upper y i e l d p o i n t to f a i l u r e versus per cent e l o n g a t i o n . The e r r o r i n these values i s the o r i g i n a l e r r o r plus the' e r r o r i n reading the d i v i s i o n s on the recorder c h a r t . The accuracy of t h i s reading i s estimated to be ±.2 of a d i v i s i o n . Using the slope of t h i s p l o t , which i s 1.2 d i v i s i o n s f o r each per cent elongation, the accuracy i s £ 0 . 1 6 7 per cent. Elongation may be expressed, i n t h i s example, as 2 6 . 7 . £ 1°48 per cent. A c a l i b r a t i o n of the thermocouple used to measure the temperature of the constant temperature both showed t h a t , at 100°C i t read 98.8°C; at 0°C i t read 0.03°C; and at —196°C i t read — 2 1 2 . 7 °C„ The voltage was taken on the same Pye p o t e n t i -ometer used during experimentation. The preceding estimates of e r r o r s do not i n c l u d e those unknown e r r o r s which are i n c u r r e d by d i s l o c a t i o n d e n s i t y , pre-sence of microstress r a i s e r s , and other such f a c t o r s . The y i e l d p oint s t r e s s i s known to be a very i n c o n s i s t e n t value. In order to analyze completely the e r r o r of y i e l d point s t r e s s , a s t a t i s -t i c a l approach i s necessary. D. METALLOGRAPHY Samples from the d i f f e r e n t l o t s were mounted i n b a k e l i t e and p o l i s h e d by u s i n g various grades of emery paper down to 0000 grade and by u s i n g a chemical p o l i s h p r e v i o u s l y described. E t c h i n g was done by immersion or swabbing u s i n g the chemical p o l i s h f o r periods greater than t h i r t y seconds. Swabbing required l e s s time and r e s u l t e d i n a three-dimensional e f f e c t . In some cases the chemical p o l i s h was f o l l o w e d by a d i f f e r e n t etch which was done by immersion f o r 90 seconds i n a s o l u t i o n of three p a r t s n i t r i c a c i d and one part h y d r o f l u o r i c a c i d . This procedure gave a quick g r a i n boundary etch. Fracture areas were examined f o r evidence of twins, but none were found. Instead, short wavy l i n e s p a r a l l e l to the f r a c t u r e surface were observed before p o l i s h i n g and e t c h i n g . These l i n e s were a l s o found i n Luder's bands, such as those shown 55 i n Figure 2 6 . This f i g u r e also shows these l i n e s at a high m a g n i f i c a t i o n . In t h i s case the l i n e s were found to p a r a l l e l to the boundaries of Luder's bands. I t was thought that they might be microcracks, but on etching they disappeared; and, furthermore, no evidence of microcracks was found i n any of the p o l i s h e d and etched specimens. mm rA L mm Figure 2 6 . Photograph of Lines found i n Luder's Bands, M i c r o s t r u c t u r e s of the v a r i o u s l o t s of tantalum are shown i n Figure 2 7 . No g r a i n boundary p r e c i p i t a t e s or i n c l u s i o n s were observed i n any of the m a t e r i a l used i n t h i s i n v e s t i g a t i o n . The m i c r o s t r u c t u r e s of the m a t e r i a l c o n t a i n i n g oxygen and the l a r g e s t amount of n i t r o g e n showed no evidence of any g r a i n -boundary p r e c i p i t a t e (see Figure 27 ( e ) , ( f ) ) . Ltch p i t s are seen i n most of these m i c r o s t r u c t u r e s . The d i f f e r e n c e i n g r a i n s i z e i s c l e a r l y evident i n these m i c r o s t r u c t u r e s . I t i s also evident that the g r a i n s i z e w i t h i n these i n d i v i d u a l specimens i s i r r e g u l a r and not equiaxed. A - Lot IM B - Lot 2M C - Lot 1WC D - Lot 2WC B - Lot 2WC F - Lot 2WC - Batch 1 - Batch 8 V DISCUSSION This inv e s t i g a t i o n has shown that tantalum follows the pattern exhibited by the other body-centered-cubic metals i n that a very strong dependence of yield-point stress on temperature e x i s t s . On a decrease i n temperature or an increase i n s t r a i n rate, the per cent elongation values go through a t r a n s i t i o n from d u c t i l e - t o - l e s s d u c t i l e behaviour as do the other body-centered-cubic metals of Group V of the periodic table. A. YIELD POINT RESULTS The temperature dependence of y l ^ l d point stress i s presented i n Figures 16, 18, 19, 21, 22, 2ht and 25. They show that as the temperature decreases the yield-point stress r i s e s continuously i n the temperature range investigated. An attempt was made to f i t the re s u l t s of these experiments to the t h e o r e t i c a l r e l a t i o n s h i p derived by Fisher 9 as described previously i n t h i s thesis; but a plot of upper .yield point stress versus the r e c i p r o c a l of absolute temperature did not y i e l d a straight l i n e . 8 The empirical r e l a t i o n s h i p of Zener and Holloman was also t r i e d but rejected, as a plot of the logarithim of y i e l d -point stress versus the r e c i p r o c a l of absolute temperature did not y i e l d a continuous straight l i n e . This plot was made up of a series of straight l i n e s indicating that the re l a t i o n s h i p was v a l i d i n c e r t a i n ranges of temperature, but that there was no consistent pattern. Therefore, no conclusions can be drawn from these r e s u l t s . .The v a l i d i t y of t h i s r e l a t i o n s h i p i n only c e r t a i n 58 ranges of temperature may be due to the effect of the various i n t e r s t i t i a l species as suggested by Snowball-^ 0 He postulated that within a certain temperature range, i n t e r s t i t i a l species react with dislocations thus anchoring them, while in a different temperature range the interacting species are different and a different relationship with yield point stress existso The results from this investigation are not complete or conclusive 33 enough to support Snowball's hypothesis„ The effects of i n t e r s t i t i a l s on the yield point stress of tantalum are quite large, as can be seen in Figures 22, 2*+, and 2 5, pages K7i 50, and 51 respectively. There is a suggestion that the same temperature dependence of yield point stress exists even after the addition of large amounts of i n t e r s t i t i a l s 0 The only difference appears to be their relative levels on the stress axis o Figure 28 shows a plot of yield point stress versus nitrogen content for several temperatures. This plot indicates that the yield point stress is a linear or near-linear function of nitrogen content in the range of temperature and range of nitrogen content investigated. This same Figure shows the effect of oxygen on the yield point stress. Lots IM and 2M were included in this plot as their analyses showed relatively high oxygen content. These points did not l i e in a straight line, probably because Lots IM and 2M had a higher nitrogen, hydrogen, and carbon content than Lots 1WC and 2WC, and because a grain,size difference is present in these materials. The slopes of these lines increase with decreasing temperature, indicating that the effect of i n t e r s t i t i a l s increases with decreasing temperature. 59 20 I 1 ' ^ > • — 0 ' 2 0 0 ' kCC 600 8 0 0 1 0 0 0 Concentration i n P a r t s Per M i l l i o n F igure 2 8 . Y i e l d - P o i n t S t r e s s versus Ni t r o g e n and Oxygen Contents„ 60 Figure 29 shows a p l o t of the y i e l d point s t r e s s versus the t o t a l i n t e r s t i t i a l c ontent 0 The points f o r m a t e r i a l w i t h the added n i t r o g e n l i e i n a s t r a i g h t l i n e as expected from the pre-vious p l o t . When the points corresponding to the m a t e r i a l with added oxygen were j o i n e d to those f o r the i n i t i a l m a t e r i a l (Lot 2WC), i t was found that the points f o r Lots IM and 2M f e l l i n the same l i n e s 0 The points corresponding to the hydrogenated m a t e r i a l were then j o i n e d to those of Lot 2WC, the s t a r t i n g materialo The r e l a t i v e e f f e c t s of i n c r e a s i n g i n t e r s t i t i a l con-te n t at a constant temperature may be assessed from t h i s p l o t c I t i s evident that the e f f e c t s are l i n e a r , . t h a t . n i t r o g e n has a greater e f f e c t than e i t h e r oxygen or hydrogen, and that hydrogen has the l e a s t e f f e c t 0 As shown i n Figure 30, the slopes of these three sets of l i n e s increase w i t h decreasing temperature Q 25 These conclusions are supported by the data of Perkins who found that n i t r o g e n a f f e c t e d the hardness much more than e i t h e r oxygen or hydrogen. 200 ppm. 6C0 ppm, 1000 ppm. F i g u r e 29, Y i e l d - P o i n t S t r e s s v e r s u s T o t a l I n t e r s t i t i a l C o n t e n t . F i g u r e 30, S l o p e s o f Y i e l d - P o i n t S t r e s s v e r s u s T o t a l I n t e r s t i t i a l C o n t e n t L i n e s v e r s u s T e m p e r a t u r e „ 6 2 The effect of i n t e r s t i t i a l content on yield point 3 stress appears to agree with the Cottrell-Bilby Theory of dislocation locking by i n t e r s t i t i a l l y dissolved elements0 Experimental results indicate that the locking effect of the i n t e r s t i t i a l s varies linearly with their concentration and that a saturation limit within the range of i n t e r s t i t i a l contents investigated is not present. The yield point stress is markedly increased by an increase in strain rate as exhibited by Lots 2M and 1WC shown in Figures 18, page hi and 19> page t+30 Kattus^observed an increase in yield point stress when testing at temperatures above room temperature. The effects of strain rate on mechanical properties can be explained by considering the frequency at which thermal fluctuations occur 0 If the rate of strain is high, a higher stress level is attained before thermal fluctuations add to the stress level to break away dislocation loops,thus i n i t i a t i n g yielding. B. DUCTILITY RESULTS The per cent elongation of pure tantalum decreases with decreasing temperature in the same manner as for single 3^ 3 ^ ' crystals of vanadium-^, polycrystalline vanadium , and 37 niobium . The transition from a ductile-to-brittle behaviour is what previous investigators 1' 1"' 1 2 ' 1^' ^ h a v e expected, but i t has never been demonstrated. The absence of a ductile-to-less ductile transition can be explained by the fact that investigators took too few values between 0°C and — 1 9 6 ° C 0 Another reason is that a b r i t t l e fracture was expected at low 63 temperatures instead of one showing a small amount of elongation,, The transition from a ductile-to-less ductile behaviour observed in this investigation is quite definite in the electron-beam melted material (Lots 1WC and 2WC). Lots 1M and 2M, which are vacuum-sintered material, also exhibit this transition but to a higher f i n a l elongation,, The materials with added amounts of nitrogen and oxygen do not show a distinct transition but rather a gradual decrease in per cent elongation as the temperature decreases„ It is interesting to note that the per cent elongation at =196°C is greater for the materials with additions than for the pure material. Lot 2WG shows less room temperature elongation than does Lot 1WC, but both exhibit the same elongation at —196°Co This variance is attributed to the different i n t e r s t i t i a l content and the different grain size of the two materials. The low per cent elongation of the purer material, i.e. Lots 1WC and 2WC, is contrary to observations on other very 37 39 pure metals ' which, upon purification, exhibit greater d u c t i l i t y at low temperatures. This unusual behaviour may be understood in terms of the following discussion. Examination of the fracture surfaces of specimens from Lots 1WC and 2WC, tested at temperatures near —196°C, revealed that deformation took place in a narrow Luder's band and that a reduction in area of 80 to 90 per cent had taken place prior to failure; i.e. the elongation was not uniform. At room tempera-ture the elongation took place uniformly, but in the transition temperature range the elongation took place in only a small part of the gauge length. The size of the deformed region decreased as the temperature decreased. To explain this low temperature behaviour i t is suggested that upon yielding, a large reduction in area takes place. This effect is much greater than the work hardening which takes place on deformation,, The result of this effect is that the shear stress necessary for fracture is reached in this narrow band and failure occurs. The fact that material with added i n t e r s t i t i a l content shows a relatively large elongation at low temperature is explained by considering the effect of the i n t e r s t i t i a l s on the work hardening a b i l i t y of the material. Since i t is probable that the work hardening a b i l i t y is increased with i n t e r s t i t i a l content, the behaviour can be explained by the following: On yielding, the greater work hardening a b i l i t y of tantalum with added i n t e r s t i t i a l s does not allow such a large i n i t i a l reduc-tion in area to take place on formation of the Luder's band; some work hardening occurs to cause more elongation before failure occurs. The shapes of load-elongation curves associated with tests of' Lots 1WC and 2WC, some of which are shown in Figure 15, page 36 , show very high sharp yield points, then a continued f a l l i n g off of the load to failure. The curves for tests below —20°C show that the high sharp yield point is followed by a very f l a t , and sometimes decreasing, work hardening portion. The load never recovered to the value achieved at the yield point The shape of these curves suggests that tantalum does not work harden5 but since tantalum does work harden , the curves indi-cate that a large reduction in area takes place on yielding. The shapes of load-elongation curves for low tempera-ture tests on materials with added i n t e r s t i t i a l elements show that the sharpness of the yield point and the associated load drop decreased with increasing i n t e r s t i t i a l content. The curves for tests conducted at temperatures near —20°C show that the load recovers to a value equal to or greater than the yield point load. These curves indicate that the I n t e r s t i t i a l content does increase the work hardening a b i l i t y of the material as has been suggested. They also indicate that the reduction in area, which occurs on the formation of the Luder's band, is not as large as that which occurs in the pure material. ' The strain rate effect on elongation is shown in the results of Lots IM, 2M, and 1WC (see Figures 16, i g , and 19*, pages 3 8 , hi, and V3 respectively). The transition becomes more abrupt and occurs at a higher temperature. There is no indica-tion of any strain rate effect on elongation at —196°C. The strain rate effects may be explained in part by the frequency of thermal fluctuations and by the probability that a thermal fluctuation of sufficient energy to release a dislocation w i l l occur in a small time increment related to the rate of strain. As the temperature decreases the probability that a fluctuation of sufficient energy w i l l occur in this small increment of time . decreases. Also as the strain rate increases, the time incre-ment decreases. Therefore, on increasing the strain rate or decreasing the temperature, the probability of releasing dislo-cations decreases. Thus larger stresses in front of disloca-tion pile-ups are achieved before thermal fluctuations and short range diffusion can take place to relieve them, resulting in the nucleation of microcracks or other mechanisms to cause failure. The elongation of the material with added hydrogen 66 exhibits a decrease from 23 per cent elongation at 100°C to a completely b r i t t l e failure at —°60°C then recovers from —120°C to 5 pe r cent elongation at —196°C„ This behaviour is similar *+l h2 to that of vanadium ? 0 The effect which has been termed hydrogen embrittlement, is thought to be due to the effect of hydrogen on the formation of cracks„ Hydrogen is thought to diffuse to microcracks and to affect their growth at tempera-tures where b r i t t l e failure is exhibited, but at lower tempera-tures or high strain rate the hydrogen is unable to diffuse to the cracks and a ductile failure results« A complete coverage of this effect can be found in the report "Hydrogen Embrittle-*+3 ment in terms of Modern Theory of Fracture" „ The elongation results for Batches 1 and 2 do not show the agreement that is shown in the results for yield point stress. The elongation of the material with the larger grain size is considerably greater than that of the other. The analysis has shown that essentially they contain the same amount of nitrogen, oxygen, carbon, and hydrogen. Therefore, i t is assumed that a different i n t e r s t i t i a l content is not the reason for the difference in elongation. The only explanation l e f t to explain this difference is that i t i s a grain size effect 0 To explain this phenomena completely, more data are needed. Any theory must explain why the large grained material with added nitrogen exhibits greater elongation than fine grained material containing nitrogen, when the reverse is true of the two materials with a low nitrogen content. VI SUMMARY AND CONCLUSIONS 1» The annealing of tantalum i s a very c r i t i c a l o p eration since many of the metals and r e f r a c t o r y m a t e r i a l s used i n furnace c o n s t r u c t i o n have appreciable vapour pressures at the temper-atures requiredo 2o The mechanical p r o p e r t i e s of tantalum and tantalum w i t h added i n t e r s t i t i a l elements e x h i b i t a strong temperature dependence 0 3o Nitrogen a d d i t i o n s increase the y i e l d s t r e s s of tantalum i n a continuous manner i n the temperature range i n v e s t i g a t e d and i n the range of n i t r o g e n contents used, ha Oxygen and hydrogen increase the y i e l d strength of tantalum w i t h i n the temperature range investigated„ 5o The r e l a t i v e e f f e c t s of the three i n t e r s t i t i a l elements are d i f f e r e n t w i t h i n the temperature range s t u d i e d , 60 The y i e l d s t r e s s of tantalum i s s t r a i n r a t e s e n s i t i v e , 7o The t r a n s i t i o n from d u e t i l e - t o - l e s s d u c t i l e type of f a i l u r e i s present i n the pure tantalum, 8, Tantalum w i t h added i n t e r s t i t i a l elements e x h i b i t s l e s s e l o n g a t i o n at room temperature than the pure m a t e r i a l , but decreases continuously to a higher el o n g a t i o n than the pure m a t e r i a l at —•196°C, A sharp t r a n s i t i o n i s not present, 9o The form of the d u c t i l e - t o - l e s s d u c t i l e t r a n s i t i o n when found i s s t r a i n r a t e s e n s i t i v e , 10, The t r a n s i t i o n temperature i s increased w i t h i n c r e a s i n g s t r a i n r a t e , 11, Y i e l d point s t r e s s of pure tantalum e x h i b i t s a dependence on g r a i n s i z e . V I I RECOMMENDATIONS FOR FUTURE WORK 1. A l a c k of f a c i l i t i e s to anneal i n a hard vacuum at tempera-tures greater than 1100 C caused much d i f f i c u l t y . I t i s recommended t h e r e f o r e , that a molybdenum tube, s i m i l a r to the s t a i n l e s s s t e e l tube used i n t h i s i n v e s t i g a t i o n be purchased . 2 0 The s c a t t e r of r e s u l t s i n d i c a t e s a non-uniform specimen. For f u t u r e work a c l o s e r c o n t r o l on preparation should be used, i . e . annealing and shapingo C y l i n d r i c a l specimens are recommended because more accuracy i s achieved i n the area measurement and a more uniform gauge length can be obtained. 3o The y i e l d s t r e s s versus temperature p l o t of Lots 1WC and 2WC suggest the presence of a S n o w b a l l ^ anomaly. I t i s suggested that zone r e f i n e d tantalum be used to determine the presence of an anoiraly. hB The data f o r m a t e r i a l c o n t a i n i n g added hydrogen and oxygen are not complete. Further work should complete these data. 5. The e f f e c t of the a d d i t i o n of carbon was not s t u d i e d . To complete t h i s study, the e f f e c t of carbon should be inves-t i g a t e d . 6. The i n d i c a t i o n of a d r a s t i c r e d u c t i o n i n area o c c u r r i n g during y i e l d i n g should be proven by h a l t i n g the t e s t as soon as y i e l d i n g has taken place and measuring the c r o s s - s e c t i o n a l area of the samples. Perhaps a d i f f e r e n t shape of specimen could a l s o help to determine the events t a k i n g place to cause the r e d u c t i o n i n the s e c t i o n of gauge length undergoing deformation. The e f f e c t of g r a i n s i z e on the d u c t i l i t y of the m a t e r i a l w i t h n i t r o g e n a d d i t i o n s should be determined by the a d d i t i o n of various amounts of n i t r o g e n to m a t e r i a l s having various g r a i n s i z e . V I I I BIBLIOGRAPHY lo Wessel, EoTo, Abrupt Y i e l d i n g and the D u c t i l e - t o - B r i t t l e  T r a n s i t i o n i n Body-Centered-Cubic Metals, J 0 Inst„ Metals, 9 No c 7," J u l y 1957, 930„ ~ 2 0 Overbach, B 0 L 0 , D.K. Felbeck, GoT 0 Hahn, and D.A. Thomas (edSo), F r a c t u r e , Technology Press, New York, 1959o 3 o C o t t r e l l , AoHo and B 0A 0 B i l b y , D i s l o c a t i o n Theory of  Y i e l d i n g and S t r a i n Ageing i n I r o n , Proceedings Royal S o c , London, A62, 19M-9* T+9* kc F i s h e r , J.Co, A p p l i c a t i o n of C o t t r e l l ' s Theory of Y i e l d i n g to Delay Y i e l d i n S t e e l , A 0S 0M 0 Transo, i±7, 19 * 5 , »f51. ~ ~ — 5o C o t t r e l l , A „ H o , D i s l o c a t i o n s and P l a s t i c Flow i n C r y s t a l s , Oxford Press, ; Clarendon England, 1953o ~" 6o Vreeland, T 0 J r D , DoSo Wood, and D 0S 0 C l a r k , A Study of the Mechanism of the Delayed Y i e l d Phenomenon, AoSoMo .Transo, J+j>, 1953, 620 0 7o G r i f f i t h , AoAo, Theory of Rupture, P h i l o s o p h i c a l Trans., Royal S o c , London, A 221, 1920, 163 0 8 0 Zener,Co, and J.H. Holloman, E f f e c t of S t r a i n Rate upon  P l a s t i c Flow of S t e e l , J c Applied P h y s i c s , 15V 19kh, 22o 9o B e c h t o l d , J.H., and P.G. Shewmon, Flow and Fr a c t u r e C h a r a c t e r i s t i c s of Annealed Tungsten, A.S.M. Trans, it6, 195k, 397. " 10o Clough, WoRo., and AoS» P a v l o v i c , The Flow, F r a c t u r e , and  Twinning of Commercially Pure Vanadium, A.S,M» Trans . / P r e p r i n t 52, 1958. l l o B e c h t o l d , J.H„, T e n s i l e P r o p e r t i e s of Annealed Tantalum at Low-Temperatures, Acta M e t a l l u r g i c a , 3, 1 9 ^ , 2k9° 12o Pugh, JoW0, Temperature Dependence of Annealed Tantalum, A.S.M. Transo ^ 8 , 1956, 6 7 7 . " ~~ 13o S c h u s s l e r , M. and J o S 0 Brunhouse J r . , Mechanical Proper-t i e s of Tantalum Consolidated by M e l t i n g , A0I0.M.E0 Transo, 2lB"T"0ctober I960, 893. l^fo Ingram, A..G., e t . a l . , Tantalum and Tantalum A l l o y s , D.M.I.C. Report 133, J u l y 25, I960, 215. 15. B a r r e t t , C.S., M e t a l l u r g y a t Low Temperatures, A.S.M.. Trans., j+g, 1957, 6 9 . ~~ 71 160 Tietz, T.E., B„A. Wilcox, J.W. Wilson, Mechanical Properties and Oxidation Resistance of Certain  Refractory Metals, Stanford Research Institute Report, SRI Project SU - 2*+36, 1958. 17. Miller, G.L., Tantalum and Niobium, Butterworths Scientific Publications, London, 1958, p. M36. 18o Schmidt, F . F . , Tantalum and Tantalum Alloys, DMIC Report 133, July 2 5 , I960, 215. 19. Ibid., P 197. 2 0 . Ibid., P 197. 2 1 . Ibid o=, P 197. 2 2 . Ibid., P 197. 2 3 . Ibid., P 197. 2ho Myers, RoH., 1950, 3 . 2 5 . Perkins, R.H., Tantalum Annealing and Degassing and Hardness Effects of Dissolved Gases, Los Alamos Scientific Laboratory Report, LA - 2136. 26. Miller, G.L., Tantalum and Niobium, Butterworths Scientific Publications, London, 1958, p. M+6. 2 7 . Ibid., p 1+56. 2 8 . Ibid., p 1+97. 2 9 . Ibid., p 1+98. 3 0 . Bakish, R0, Some Observations on the Effect of the Interaction of Tantalum with Oxygen, Nitrogen  and Hydrogen, J. of the Electrochemical Society 105 No. 10, October 1958, 57^. 3 1 . Seghezzi, H.D., E. Gebhardt and W. Durrschnabel, New Investigations .'into the Tantalum-Nitrogen System, 3rd Plansee Seminar, Reutte, Austria, 1958, 291. 3 2 . Gebhardt, E,, and H.D. Seghezzi, New Investigations into the Tantalum-Oxygen System, 3rd Plansee Seminar, Reutte, Austria, 1958, 280. 3 3 . Snowball, R.F., M.A. Sc. Thesis submitted in the Department of Mining and Metallurgy, University of British Columbia, October I960. 3*+. Fraser, RCW., M.A. Sc. Thesis submitted in the Department of Mining and Metallurgy, University of Br i t i s h Columbia, November, I960. 72 35. Miller, G.L., Tantalum and Niobium, Butterworths Scientific Publications, London 1958, p. 1+5l+. 36o Operating Instructions for the Instron Tensile Tester, Manual No. 155? Instron Engineering Corporation, Canton, Massachusetts, 17. 37o Mincher, A.L. and W.F. Sheely, Effect of Structure and  Purity on the Mechanical Properties of Columbium, A.I.M.E. Transo 221 No0 1, February 1961, 19. 38. Wessel, E.To, Some Exploratory Observations of the Tensile Properties of Metals at Very Low  Temperatures, Ao.S..M. Trans,, M-9, Preprint No. 3, 1956. 39. Smith, R.L. and J.L. Rutherford, Tensile Properties of Zone Refined Iron in the Temperature Range  from 298° to if.2oK., J. of Metals 9 No. 7, July 1957, 857o ~ h00 Miller, G.L., Tantalum and Niobium, Butterworths Scientific Publications, London 1958, p. *+20. hl0 Roberts, B.W. and H.C. Rogers, Observations of Hydrogenated Vanadium, A.I.M.E. Trans., 206, October 1956, 1213. *+2. Loomis, B.A. and O.N. Carlson, Investigation of the Ductile-to-Brittle Transition in Vanadium, Paper Presented at the Reactive Metals Conference, May 27-29, 1958. if3 . Blanchard, P.A., and A.R. Troiano, Hydrogen Embrittle-ment in Terms of Modern Theory of Fracture, WADC Technical Report 59-Wf, August 1959. 7 3 APPENDIX A TABLE V I I THE RESULTS OF TENSILE Ultimate T e n s i l e Test Temp. °C Stress No. x 103p 1 21 56.0 2 21 58.6 3 21 63 o 2 4 21 54.3 5 7 58oO 6 7 6 0 . 0 7 0 59*5 8 0 6 0 o 0 9 0 59.7 10 0 58.8" 11 -12 59.8 12 -12 63 .4 13 -43 64.2 14 -43 64o5 15 -50 67.0 16 -55 72 o 8 17 -55 7 0 . 6 18 -68 . 77»0 19 -68 77,8 20 -98 80 „ 4 21 „ 9 8 84.6 22 -138 91.7 23 - 1 3 8 96.6 24 -195 119.0 25 -195 132.0 26 -195 134.2 27 -175 114.0 28 -175 114.0 29 -195 116.0 30 -195 115.0 31 - 1 8 4 1 1 8 . 2 32 - 1 8 4 120.0 33 -195 _ 34 -195 -35 -175 -3 6 -175 -37 23 -38 23 -3 9 11 -40 11 -41 - 5 -42 ~ 5 -43 - 19 -44 - 19 _ TESTS ON TANTALUM LOT 1M. Upper Y i e l d S t r a i n S t r e s s Rate Percent x lO^psi. in/in/min. Elongation 47.4 '.067 2 9 . 2 50.4 .067 27.2 55.0 .067 2 8 . 1 4 7 . 0 .067 2 7 . 0 50.0 .067 4 9 . 0 .067 48.7 .067 2 2 . 8 52.2 .067 2 5 . 2 48.6 .067 2 8 . 0 5 1 . 8 .067 — 52.2 .067 5 3 . 8 .067 2 8 . 4 58.3 .067 2 9 . 4 6 1 . 6 .067 2 4 . 6 6 1 . 6 .067 29.8 6 5 . 0 .067 3 0 . 2 6 4 o 0 .067 2 3 . 4 6 4 o 8 .067 2 5 . 6 70.0 .067 3 0 . 4 7 8 . 8 .067 2 4 . 6 7 9 . 6 .067 2 2 . 8 9 1 . 7 .067 23.0 92.5 .067 2 4 . 5 119.0 .067 5.0 1 3 2 . 0 .067 8.6 1 3 4 . 2 .067 1 1 . 4 1 1 4 . 0 .067 1 7 . 8 1 1 4 . 0 .067 14.2 1 1 6 . 0 .067 8.0 1 1 5 . 0 .067 6.8 1 1 8 . 2 .067 8.34 1 2 0 . 0 .067 8.34 26.7 4.18 26.7 3.75 26.7 4.18 26.7 4.18 26-7 22.1 26.7 25 .0 26.7 20.4 26.7 20.8 26.7 25.0 26.7 26.8 26.7 21.2 26.7 24.2 Ultimate T e n s i l e Test Temp, °C Stress No, x 103psi 45 - 35 46 - 35 -47 - 50 _ 48 - 50 _ 49 - 74 50 - 74 -51 - 80 — 52 - 80 -53 - 95 -54 - 95 55 -110 56 -110 57 -125 — 58 -184 -59 -184 — 60 15 — 61 15 -62 10 — 63 10 — 64 5 65 - 60 66 - 60 67 -.140 _ 68 -140 -Upper Y i e l d S t r a i n S t r e s s Rate Percent x lO^psi. in./in./min. Elongation 26.7 20.0 26.7 22.9 26.7 18.8 26.7 22.0 26.7 14.6 26.7 8.75 26.7 8.34 26.7 8.34 26.7 7.5 26.7 7.5 26.7 7.3 26.7 7.3 26.7 7.5 26.7 6.25 26.7 4.17 26.7 25.0 26.7 20.8 26.7 23.0 26.7 25.0 26.7 25.0 26.7 17.3 26.7 15.0 26.7 5.2 26.7 8.0 1 APPENDIX B TABLE VIII THE RESULTS OF WORK HARDENING AND AGING TEST Ultimate Upper Aging Tensile Y i e l d Strain Percent Temp. ' Test Tempo°C Stress Stress Rate Percent Cold for 1 No. x 10-^ pi i. x lO-^ ps i. in/in/min. Elongation Work Hour 1 21 6 7 . 66.0 . 0 6 7 8 A 1 0 2 21 79.2 77.2 . 0 6 7 1.*+ 25 -3 -195 l*f5o2 137.2 . 0 6 7 5.2 1 0 -if = 1 9 5 1^5.5 138.0 . 0 6 7 6.2 1 0 -5 -195 165 = 0 153.0 . 0 6 7 5.6 25 -6 -195 159.0 159.0 . 0 6 7 If.If -7 -195 161.5 1^9.0 . 0 6 7 2oh ho 8 -195 156.5 lUif.O . 0 6 7 2 . 6 hO = 9 -195 1 6 0 . 5 1^9.0 . 0 6 7 2.0 . 50 10 -195 16*f.3 156.0 . 0 6 7 5.2 5o -' 11 -195 1 3 8 . 5 1 3 8 . 5 . 0 6 7 7.2 1 0 7 0 0 12 -195 iho.5 1^0.5 . 0 6 7 5 . 6 1 0 7 0 0 13 -195 151.3 1^ 9 . 5 . 0 6 7 5.0 25 7 0 0 11+ -195 1^+9.5 1^ 9 . 5 . 0 6 7 6 . 3 25 7 0 0 15 -195 136.0 136.0 . 0 6 7 h.h 1 0 ifOO 16 -195 1 3 3 . 5 1 3 3 . 5 . 0 6 7 5oh 1 0 hoo 1 7 21 73.0 70. h . 0 6 7 h02 1 0 hOO 18 21 9 3 . 8 9 1 . 6 . 0 6 7 1.0 25 hOO 1 9 -195 1^ 5 . 5 1^ 5 . 5 . 0 6 7 3.2 25 hOO 20 - 1 9 5 l>+2.0 1^2.0 . 0 6 7 3oh 25 - hOO 21 23 9 6 . 5 9 6 . 5 = 0 6 7 1.2 25 300 22 23 9 3 . 5 9 3 . 5 . 0 6 7 1.2 25 300 23 23 78.2 78.2 . 0 6 7 6 . 3 1 0 300 2h 23 70 .7 70.2 . 0 6 7 8 . 3 1 0 300 25 - 1 9 5 1 +^8.0 lk&a0 . 0 6 7 6 . 3 10 300 26 -195 1^9.0 1 +^9.0 . 0 6 7 i+.l 10 300 27 -195 167.0 167.0 . 0 6 7 h.l 25 300 28 . -195 158.5 1 5 8 . 5 o 0 6 7 3.h 25 300 APPENDIX C 76 TABLE IX THE RESULTS OF TENSILE TESTS ON TANTALUM LOT 2M Ultimate Upper T e n s i l e Y i e l d S t r a i n Test Temp„ °C Stre s s S t r e s s Rate Percent No. x 103psj. x KPpai. i n / i n / min. Elongation 1 21 68.8 63.2 .0267 29.2 2 21 71»6 62.8 .0267 30.2 3 21 78,8 72.2 .0267 25.0 4 21 7 9 o 2 71.7 .0267 .23.5 5 Q 8 0 . 8 71.7 .0267 27.2 6 0 8 0 . 0 71.0 .0267 31.2 7 - 20 94.0 87.8 .0267 27.1 8 • - 20 95.0 82.2 .0267 27.1 9 - 20 91.6 84.O .0267 27.1 10 - 40 89.0 88.2 .0267 27.1 11 - 40 8 1 . 0 87.7 .0267 27.1 12 - 6 0 92.2 85.0 .0267 26.0 13 - 60 83.5 81.7 .0267 33.4 14 - 6 0 9 3 . 0 84.7 .0267 33 .4 15 - 80 91.8 87.2 .0267 29.2 16 - 80 90.5 87.7 o 0 2 6 7 31.4 17 -100 97.4 97.4 .0267 29.2 18 -100 9 9 . 0 9 8 , 0 o 0 2 6 7 27.0 19 -120 109.7 109.7 .0267 25.0 20 -220 1 0 8 . 0 107.0 .0267 16.7 21 - 1Q 86.7 76.0 .0267 25.0 22 - 20 84.0 75.5 .0267 27,8 23 - 2Q 8 1 . 7 74.6 .0267 27.8 24 - 20 84.2 74.6 .0267 25.0 25 - 20 84.2 76.8 ,0267 27.8 26 - 30 84.2 76.6 .0267 — 27 - 30 88.2 78.8 .0267 25.0 28 -195 156.0 156.0 .0267 10.0 29 -195 161.8 161.8 .0267 10.4 30 -195 158.0 158.7 .0267 10.0 31 -195 145.0 145.0 .0267 10.4 32 -195 147.2 147.2 .0267 9.4 33 -195 149.0 149.0 .0267 10.4 34 -195 161.0 161.0 .0267 9.4 35 21 88.6 83.0 2.67 26.5 36 21 87.0 82.5 2 . 6 7 25.0 37 0 88 o 4 83.4 2.67 25.0 38 0 88.4 82.4 2.67 25.0 39 - 20 89.6 89.6 2.67 18.8 40 - 20 90.2 82.0 2.67 24.0 41 - 20 88.0 83.6 2.67 31 .0 42 - 4 0 90.8 9 0 . 0 2.67 24.0 43 - 40 93.0 88.0 2.67 23.0 4 4 - 60 88.5 88.5 2.67 20,8 Ultimate Tensile Test Temp. °C Stress No. X lO^psi 4 5 - 60 9 4 . 0 4 6 - 6 0 9 3 . 0 4 7 - 60 92.0 4 8 - 80 1 0 7 . 0 4 9 - 80 1 0 7 . 5 50 - 8 0 1 0 0 . 2 5 1 - 1 0 0 1 1 6 . 5 52 - 1 0 0 1 1 1 . 0 53 - 1 0 0 1 0 6 . 0 54 - 1 0 0 1 1 5 . 0 55 - 1 2 0 1 1 8 . 8 5 6 -12Q 1 1 8 . 0 5 7 - 1 3 0 1 2 1 . 0 58 - 1 3 0 1 2 2 . 5 59 - 1 3 0 1 2 8 . 0 60 - 1 9 5 1 5 5 . 0 61 - 1 9 5 1 6 1 . 0 6 2 - 1 9 5 1 5 7 . 2 63 - 1 9 5 1 6 3 . 2 Upper Yield Strain Stress Rate Percent x 103psi. in/in/min, Elongation 9 2 . 5 2.67 25.0 89.5 2.67 25.0 - 2.67 25.0 107.0 2.67 27.2 107.0 2.67 26.1 100.2 2.67 26.0 116.5 2.67 16.7 111.0 2.67 20.8 106.0 2.67 23.0 115.0 2.67 12.5 118.8 2.67 14.6 118.0 2 . 6 7 12.5 _ 2.67 12.5 122.5 2.67 12.0 128.0 2.67 1 4 . 6 155.0 2.67 9.4 161.0 2.67 9.4 157.2 2.67 9.4 163.2 2.67 9.4 APPENDIX D TABLE X THE RESULTS OF TENSILE TESTS ON TANTALUM LOT 1 W C Ultimate Upper Tens i l e Y i e l d S t r a i n Test Temp„ °C S t r e s s S t r e s s Rate Percent No, x lO-^si x lO^psi. in/in/min. Elongation 1 1 0 Q 3 0 o 2 2 5 . 4 . 0 2 6 7 4 4 . 0 2 5 0 3 0 o 5 2 4 0 8 . 0 2 6 7 4 6 . 0 3 2 2 3 3 o 7 3 1 . 8 . 0 2 6 7 4 0 . 5 4 2 2 3 2 o 2 2 6 . 5 . 0 2 6 7 3 9 . 0 5 2 2 3 1 » 9 2 5 . 2 o 0 2 6 7 4 2 . 0 6 2 2 3 3 o 9 23 0 8 . 0 2 6 7 4 2 . 0 7 0 3 5 c 6 3 0 . 8 . 0 2 6 7 4 1 . 5 8 0 3 6 „ 1 3 4 . 4 . 0 2 6 7 4 0 . 0 9 0 3 8 . 1 3 8 . 1 . 0 2 6 7 4 1 . 0 1 0 0 3 9 » 5 3 9 . 5 . 0 2 6 7 4 0 . 0 1 1 - 2 0 3 7 o l 3 7 . 1 1 0 2 6 7 3 6 . 0 1 2 - 2 0 3 6 o 9 3 8 . 2 . 0 2 6 7 4 6 . 0 1 3 - 2 0 4 2 . 8 4 2 . 8 . 0 2 6 7 3 7 . 5 1 4 - 2 0 3 7 o 2 3 6 . 5 . 0 2 6 7 4 0 . 0 1 5 - 2 Q 3 5 o 7 3 5 . 0 . 0 2 6 7 3 0 . 5 1 6 - 2 0 3 5 c 7 3 5 ° 7 . 0 2 6 7 1 7 - 3 5 4 3 o O 4 3 .0 . 0 2 6 7 3 5 . 5 18 - 3 5 4 3 o O 4 3 . 0 o 0 2 6 7 3 4 » 0 1 9 - 4 0 4 6 0 2 4 6 . 2 . 0 2 6 7 3 2 . 5 2 0 - 4 0 4 4 o 4 4 4 0 4 . 0 2 6 7 4 1 . 5 2 1 - 4 5 4 0 o 5 4 0 . 5 . 0 2 6 7 3 5 . 5 2 2 - 4 5 4 3 o 2 4 3 0 2 . 0 2 6 7 3 7 . 0 2 3 - 4 5 4 4 . 0 4 4 . 0 . 0 2 6 7 3 3 . 0 2 4 - 4 5 4 1 . 5 4 1 . 5 . 0 2 6 7 — 2 5 - 5 0 4 2 . 2 4 2 . 0 . 0 2 6 7 2 9 . 0 2 6 - 50 4 6 . 3 4 6 . 3 . 0 2 6 7 3 6 . 0 2 7 - 5 0 4 7 . 4 4 7 . 4 . 0 2 6 7 2 9 . 0 28 - 5 5 5 2 . 5 5 2 . 5 . 0 2 6 7 1 6 . 0 2 9 - 5 5 4 7 . 0 . 4 7 . 0 . 0 2 6 7 3 0 - 5 5 5 3 o O 5 3 . 0 . 0 2 6 7 _ 3 1 - 5 5 4 8 . 7 4 8 . 7 . 0 2 6 7 — 3 2 - 60 4 7 . 0 4 7 . 0 . 0 2 6 7 2 4 . 0 3 3 - 60 4 7 . 8 4 7 . 8 . 0 2 6 7 3 2 . 5 3 4 - 6 0 5 0 . 4 5 0 . 4 . 0 2 6 7 3 2 . 0 3 5 - 7 0 4 7 . 2 4 7 . 2 . 0 2 6 7 2 2 . 0 3 6 - 7 0 5 4 . 3 5 3 . 6 . 0 2 6 7 1 2 . 7 3 7 - 7 0 5 0 . 2 5 0 . 2 0 O 2 6 7 — 3 8 -'80 51 . 6 5 1 . 6 . 0 2 6 7 2 0 . 0 3 9 - 80 4 9 . 0 4 9 . 0 . 0 2 6 7 8 . 0 4 0 - 9 0 5 9 . 0 5 9 . 0 . 0 2 6 7 1 2 . 7 4 1 - 9 0 5 4 . 0 5 4 o O . 0 2 6 7 1 3 . 3 4 2 - 1 0 0 5 7 . 6 5 7 . 6 . 0 2 6 7 9 . 0 4 3 - 1 0 0 5 8 . 8 5 8 . 8 . 0 2 6 7 — 4 4 - 1 0 0 6 6 . 2 6 6 . 2 . 0 2 6 7 4 . 5 THE'RESULTS OF TENSILE TESTS ON TANTALUM LOT IWC 7 9 Ultimate T e n s i l e Test Temp. °C Stress No, x lO-'p&i. 4 5 - 1 2 0 . 6 8o 5 4 6 - 1 2 0 . 6 5 o 5 4 7 - 1 2 0 7 0 . 8 4 8 - 1 3 2 7 2 . 2 4 9 - 1 4 0 6 9 . 6 5 0 - 1 4 0 3 5 . 0 5 1 - 1 9 5 1 0 7 . 0 5 2 - 1 9 5 1 0 8 . 5 53 1 0 0 3 5 . 0 5 4 2 2 3 8 . 0 5 5 2 2 3 6 . 2 5 6 0 4 1 . 8 5 7 0 4 1 . 7 5 8 - 2 0 4 9 . 8 5 9 - 2 0 5 5 . 8 6 0 - 4 0 5 5 . 5 6 1 - 4 0 5 6 . 0 6 2 - 60 5 8 . 8 6 3 - 6 0 60 .5 6 4 - 80 6 6 . 7 6 5 - 80 6 4 . 4 6 6 - 1 2 0 7 8 . 0 6 7 - 1 2 0 7 9 . 8 6 8 - 1 9 5 1 0 5 . 0 6 9 - 1 9 5 1 0 7 . 0 7 0 - 1 9 5 1 1 3 . 0 Upper Y i e l d S t r a i n S t r e s s Rate Percent x 10-^ ps't. ia/in/min. Elongation. 6 8 . 5 . . 0 2 6 7 4 . 5 6 5 . 5 . 0 2 6 7 7 0 . 8 . 0 2 6 7 3 . 0 7 2 . 2 . 0 2 6 7 2 . 5 6 9 . 6 . 0 2 6 7 2 . 0 8 5 . 0 . 0 2 6 7 2.0 1 0 7 . 0 . 0 2 6 7 < 1 108 .5 . 0 2 6 7 < 1 3 5 . 0 2 . 6 7 „ 3 8 . 0 2 . 6 7 4 6 . 0 3 6 . 2 2 . 6 7 3 9 . 0 4 1 . 8 2 . 6 7 4 1 . 7 2 . 6 7 3 5 . 0 4 9 . 8 2 . 6 7 1 0 . 0 5 5 . 8 2 . 6 7 3 . 0 5 5 . 5 2 . 6 7 — 5 6 . 0 2 . 6 7 6 . 0 5 8 . 8 2 . 6 7 _ 60 . 5 2 . 6 7 < 1 6 6 . 7 2 . 6 7 ^ 1 6 4 . 4 2 . 6 7 < 1 7 8 . 0 2 . 6 7 < 1 7 9 . 8 2 . 6 7 < 1 1 0 5 . 0 2 . 6 7 *L1 1 0 7 . 0 2 . 6 7 < 1 1 1 3 . 0 2 . 6 7 < 1 80 APPENDIX E TABLE XI THE RESULTS OF TENSILE TESTS ON TANTALUM LOT 2WG Ultimate Upper T e n s i l e Y i e l d S t r a i n Test Temp. °C Stre s s S t r e s s Rate Percent No. x 103psi. x 10-^ pei. i n / i n . / min. Elongation 1 100 4 0 o 7 28 = 8 = 0267 2 5 o 5 2 50 38 = 8 31 = 8 o 0 2 6 7 33 = 5 3 22 44 o 8 36 = 2 0 O 2 6 7 28 = 0 4 0 4 7 o 3 37 = 6 = 0267 33 = 0 5 - 20 50„2 50 = 2 0 O 2 6 7 29 = 0 6 - 40 5 2 o 2 51=5 o 0 2 6 7 29 = 0 7 - 60 6 3 o 6 63 = 6 = 0267 21 = 5 8 - - 80 6 4 o 7 64 = 7 = 0267 17=5 9 -100 7 0 o 0 70 = 0 = 0267 11 = 0 10 -100 68„3 68 = 3 = 0267 9 = 0 . 11 -120 9 0 o 4 90 = 4 = 0267 13 0 5 12 -126 7 9 o 4 79 = 4 = 0267 7 = 0 13 -140 82 = 2 82 = 2 o 0 2 6 7 60O 14 -195 122 o 5 122 = 5 = 0267 <1 15 -195 129 = 0 129 = 0 o 0 2 6 7 <1 APPENDIX F TABLE X I I THE RESULTS OF TENSILE TESTS ON TANTALUM LOT IWC BP TCH 1 Ultimate Upper T e n s i l e Y i e l d S t r a i n Test Temp, °C St r e s s Stress Rate Percent No. x lo -^psi. x 10-*p%». in/in/min. Elongation 1 1 0 0 8 5 . 8 80 . 4 . 0 2 6 7 1 6 . 2 2 2 2 9 9 . 4 9 8 . 2 . 0 2 6 7 1 2 . 5 3 0 1 1 2 . 0 1 0 9 . 0 . 0 2 6 7 1 0 . 5 4 - 2 0 1 0 3 . 2 1 0 2 . 5 . 0 2 6 7 1 1 . 5 5 - 4 0 1 2 1 . 0 1 2 1 . 0 . 0 2 6 7 8 . 0 6 - $ 0 1 2 6 . 5 1 2 6 . 5 . 0 2 6 7 — 7 - 7 0 1 2 1 . 0 1 2 1 . 0 . 0 2 6 7 8 . 5 8 - 9 0 1 3 6 . 5 1 3 6 . 5 . 0 2 6 7 8 . 5 9 - 1 1 0 1 4 5 . 0 1 4 5 . 0 . 0 2 6 7 2 . 0 1 0 - 1 3 0 1 5 1 . 5 1 5 1 . 5 0 O 2 6 7 4 . 0 1 1 - 1 9 5 208 . 0 208 . 0 . 0 2 6 7 2 . 0 1 2 - 1 9 5 1 9 9 . 0 1 9 9 . 0 . 0 2 6 7 3 . 5 TABLE X i n THE RESULTS OF TENSILE TESTS ON TANTALUM LOT ' 2WC BATCH 2 Ultimate Upper Temp. °C T e n s i l e Y i e l d S t r a i n Test S t r e s s S t r e s s Rate Percent No. X lO^psi. X lO^psi. i n / in/min. Elongation 1 1 0 0 7 9.8 7 6 . 5 . 0 2 6 7 2 3 . 0 2 5 0 9 2 . 3 9 0 . 1 . 0 2 6 7 2 0 . 0 3 2 2 1 0 2 . 0 1 0 2 . 0 o 0 2 6 7 2 4 . 0 4 - 60 1 3 1 . 5 1 3 1 . 5 . 0 2 6 7 2 0 . 0 5 - 6 0 1 2 4 . 0 1 2 4 , . 0 . 0 2 6 7 2 1 . 0 6 - 80 138 . 0 138 . 0 . 0 2 6 7 — 7 - 1 0 7 1 4 0 . 0 1 4 0 . 0 . 0 2 6 7 1 4 . 5 8 - 1 2 0 1 4 9 . 4 1 4 9 . 4 . 0 2 6 7 1 8 . 5 9 - 1 4 0 1 6 7 . 5 1 6 7 . 5 . 0 2 6 7 1 3 . 5 1 0 - 1 9 5 2 0 4 . 0 2 0 4 . 0 . 0 2 6 7 8 . 5 1 1 - 1 9 5 2 0 0 . 0 2 0 0 . 0 . 0 2 6 7 8 . 5 TABLE XIV THE RESULTS OF TENSILE TESTS ON TANTALUM LOT 2WC BATCH 3 Ultimate Upper Tensile Yield Strain Test Temp. °C Stress Stress Rate Percent No. x lO-^ psi. x lO-^psi. in/in/min. Elongation 1 22 45.5 44.6 .0267 24.0 2 0 53.5 53.5 .0267 18.0 3 - 20 60.0 60.0 .0267 18.0 4 - 40 61.5 61.5 .0267 26.0 5 - 60 61.0 61.0 .0267 13.0 6 - 80 71.7 71.7 .0267 12.0 7 -100 74.5 74.5 .0267 8.5 8 -103 78.2 78.2 .0267 9.0 9 -120 92.5 92.5 .0267 6.0 10 -132 — — .0267 8.5 11 -136 89.3 89.3 .0267 6.0 12 -195 122.0 122.0 .0267 2.0 TABLE XV THE RESULTS OF TENSILE TESTS ON TANTALUM LOT 2WC BATCH .4 Ultimate Upper Tensile Y i e l d Strain Test Temp. °C Stress Stress Rate Percent No. x 103p&\. x lO-^psi. i n / i n / min. Elongation 1 10Q 46.5 39.6 .0267 26 .0 2 51 50.6 4 8 . 4 .0267 26 .0 3 22 49.4 43 .2 .0267 30.5 4 0 50.0 47.7 .0267 3 0 . 0 5 - 20 53.2 53.2 .0267 25 .0 6 - 40 60.5 60 .5 .0267 21.0 7 - 60 67.3 67.3 .0267 14.5 8 - 80 73.4 73.4 .0267 17.5 9 -100 87.2 87 .2 .0267 8.0 10 -100 87.8 87.8 .0267 15 .0 11 -120 89.3 89.3 .0267 9 . 0 12 -133 96 .0 96 .0 .0267 8 .0 13 -137 94.4 94.4 .0267 6.5 14 -195 131.5 131.5 .0267 2 .0 TABLE XVI THE RESULTS OF TENSILE TESTS ON TANTALUM LOT 2WC BATCH 5 Ultimate Upper Tens i l e Y i e l d S t r a i n Test Temp. °C St r e s s Stress Rate Percent No. x 103psi. x 103psi. in./ in/min. Elongation 1 100 75.5 69.0 .0267 21.5 2 58 100.5 75.6 .0267 21.5 3 22 81.4 81.4 o 0 2 6 7 20.5 4 22 82.2 82.2 .0267 22.0 5 0 90.4 90.4 .0267 18.0 6 - 20 94.4 94«4 .0267 15.0 7 - 40 100.3 100.3 .0267 17.0 8 - 60 111.5 111.5 .0267 = , 9 - 60 116.0 116.0 .0267 17.0 10 - 80 114.0 114.0 .0267 13 0 5 11 -100 124.7 124.7 .0267 8.5 12 -120 134.2 134.2 .0267 10.5 13 -136 145.0 145.0 .0267 13.5 14 -195 184.0 184.0 .0267 9.0 15 -195 184.3 184.3 .0267 10.5 TABLE XVII THE RESULTS OF TENSILE TESTS ON TANTALUM LOT 2WC BATCH 6 Ultimate Upper T e n s i l e Y i e l d S t r a i n Test Temp. °C Stre s s Stress Rate Percent No. x 103psi. x 103p&'i, • in/in/min. E l o n g a t i o n 1 100 53.9 52.5 .0267 20.0 2 50 47.7 42.2 o 0 2 6 7 24.0 3 22 46.5 44.0 .0267 19.0 4 0 52.2 52.2 .0267 22.0 5 - 20 57.7 53.8 .0267 23.0 6 - 40 66.2 66.2 .0267 19.0 7 - 6 0 70.7 70.7 .0267 17.0 8 - 80 69.4 69.4 .0267 17.0 9 -100 81.6 81.6 .0267 10.5 10 -124 93.7 93.7 .0267 11.5 11 -140 96.2 96.2 .0267 - 12.0 12 -195 131.2 131.2 .0267 3.0 TABLE XVIII THE RESULTS OF TENSILE TESTS ON TANTALUM LOT 2WC BATCH 7 Ultimate Upper Tensile Yield Strain Test Temp. °C Stress Stress Rate Percent No. x 10-7>si. x lO-^ psi. • in/in,/min. Elongation 1 100 57.4 52.4 .0267 18.5 2 50 68.6 63.6 .0267 16.0 3 22 68.7 66.0 .0267 20.5 4 - 2Q 75.5 75.5 .0267 20.5 5 •- 4 0 83.4 81.7 .0267 19.0 6 - 60 88.0 88.0 .0267 1 9 . 0 7 - so 9 0 . 4 90.4 .0267 16.0 8 -105 1 0 7 . 2 1 0 7 . 2 .0267 12.0 9 -120 106.0 106.0 .0267 6.0 10 - 1 4 0 108.5 108.5 .0267 7.0 APPENDIX G 85 TABLE XIX THE RESULTS OF TENSILE TESTS ON TANTALUM LOT 2WC BATCH 8 Ultimate Upper Temp. °C Ten s i l e Y i e l d S t r a i n Test St r e s s S t r e s s Rate Percent No. x 10-^psi x 10-*p* in/in/min. Elongation 1 1 0 4 1 1 7 . 0 8 4 . 4 . 0 2 6 7 1 5 o 0 2 5 1 9 9 . 7 9 9 . 2 . 0 2 6 7 1 4 o 0 3 2 2 9 8 . 8 9 8 . 8 . 0 2 6 7 1 6 . 5 4 0 9 7 . 5 9 7 . 5 o 0 2 6 7 1 6 . 0 5 - 2 0 1 0 4 . 2 104 o 2 . 0 2 6 7 1 4 . 5 6 - 4 0 1 1 0 . 5 1 1 0 . 0 . 0 2 6 7 2 0 . 0 7 - 60 1 1 9 . 0 119.0 0 O 2 6 7 1 0 . 0 8 - 80 1 1 2 . 0 1 1 2 . 0 . 0 2 6 7 4 . 5 9 - 1 0 0 1 2 6 . 5 1 2 6 . 5 . 0 2 6 7 • 4 o 0 1 0 - 1 1 9 1 4 1 . 5 1 4 1 . 5 . 0 2 6 7 3 . 0 1 1 - 1 3 8 1 5 3 . 5 1 5 3 o 5 . 0 2 6 7 2 . 5 1 2 = 1 9 5 2 0 0 . 0 2 0 0 . 0 . 0 2 6 7 5 . 0 86 APPENDIX H  TABLE XX THE RESULTS OF TENSILE TESTS ON TANTALUM LOT 2WC BATCH 9 Ultimate Upper Temp„°C Te n s i l e Y i e l d S t r a i n Test Stress S t r e s s Rate Percent No, x IO^psi. x lO-^psi. i n . / i n / min. Elongation 1 1 0 3 4 3 o 7 2 8 . 3 .0267 2 3 . 0 2 22 4 0 o 2 4 0 »2 . 0 2 6 7 5 o 0 3 - 2 3 460 4 4 6 o 4 . 0 2 6 7 1.0 4 - 60 53.2 53.2 .0267 0 5 - 80 6 0 o 7 6 0 o 7 . 0 2 6 7 0 6 - 1 0 5 71.3 71.3 . 0 2 6 7 0 7 - 1 3 1 8O08 8 0 o 8 . 0 2 6 7 2.0 8 - 1 9 5 1 3 5 o 5 1 3 5 . 5 . 0 2 6 7 3 o 0 

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