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

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EMBRITTLEMENT OF ZINC CRYSTALS BY MERCURY by" JYUNG-HOON KIM A THESIS SUBMITTED IN PARTIAL FULFILMENT , OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE IN THE DEPARTMENT OF METALLURGY We accept t h i s t h e s i s as conforming t o the standard r e q u i r e d from candidates f o r . the degree of MASTER OF APPLIED SCIENCE THE UNIVERSITY OF BRITISH COLUMBIA January, 1966. 1 I n p r e s e n t i n g 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 r e q u i r e m e n t s 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 that, the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r  m i s s i o n f o r e x t e n s i v e c o p y i n g 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 g r anted 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 . c o p y i n g 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 - n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n * Department of M e t a l l u r g y The U n i v e r s i t y of B r i t i s h Columbia, Vancouver 8 , Canada Date F e b r u a r y 15th, 1966  T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A V A N C O U V E R 8, C A N A D A D E P A R T M E N T OF M E T A L L U R G Y F e b r u a r y 11th, 1966. • C O M M E N T S ON T H E S I S " E m b r i t t l e m e n t of Z i n c C r y s t a l s by M e r c u r y " by Jyung-Hoon K i m A t the o r a l p r e s e n t a t i o n h e l d i n the D e p a r t m e n t of M e t a l l u r g y on Wednesday, J a n u a r y 26, 1966, i t was d e c i d e d that the t h e s i s s h o u l d be a c c e p t e d , but w i t h the f o l l o w i n g comments: 1. The q u a l i t y of the E n g l i s h c o m p o s i t i o n i s w e l l b e l o w the u s u a l s t a n d a r d n o r m a l l y e x p e c t e d of students whose n a t i v e language i s . E n g l i s h . H o w e v e r , by m a j o r i t y o p i n i o n , i t was a g r e e d that i n a ca s e where E n g l i s h i s not a student's m o t h e r language, i t i s p r e f e r a b l e that the t h e s i s be w r i t t e n i n i m p e r f e c t E n g l i s h a n d r e p r e s e n t the student's own w r i t i n g and t h i n k i n g , than to have p e r f e c t E n g l i s h a r i s i n g f r o m e x t e n s i v e r e w r i t i n g o r r e v i s i o n by the s u p e r v i s o r . The o v e r r i d i n g c o n s i d e r a t i o n , h o w e v e r , m u s t be that the t h e s i s s h a l l be s u f f i c i e n t l y w e l l w r i t t e n to a v o i d any a m b i g u i t y of thought o r m i s s t a t e m e n t s of f a c t . 2. It was f e l t that some of the d e t a i l e d c o n c l u s i o n s e x p r e s s e d i n t h i s t h e s i s w e r e u n w a r r a n t e d by the n a t u r e of the r e s u l t s . . H o w e v e r , i t was f e l t that t h i s c o u l d be due, i n p a r t , to the language p r o b l e m , and that i n any c a s e , the q u a l i t y of the w o r k g e n e r a l l y w a r r a n t e d i t s a c c e p t a n c e . i ABSTRACT A study has been undertaken t o i n v e s t i g a t e the l o s s of d u c t i l i t y and m o d i f i e d work hardening c h a r a c t e r i s t i c s of z i n c s i n g l e c r y s t a l s coated w i t h mercury. Important r e s u l t s of t e n s i l e t e s t s performed under f i x e d experimental c o n d i t i o n s are summarized t o be: (1) increase i n c r i t i c a l r e s o l v e d shear s t r e s s , and increase of work hardening slope i n stage A and stage B (2) decrease i n t r a n s i t i o n ' s t r a i n from stage A t o stage B (3) decrease i n f r a c t u r e s t r e s s and f r a c t u r e s t r a i n . The r e s u l t s have been i n t e r p r e t e d i n the context of the present understanding of deformation theory of C.P.Hex. metals. In a d d i t i o n , r e l e v a n t mechanisms f o r crack i n i t i a t i o n have been s t u d i e d w i t h the aid- of microscopic observations o f deformed c r y s t a l s . i i ACKNOWLEDGEMENT The author g r a t e f u l l y acknowledges the guidance of Dr. E. Teghtsoonian, the d i r e c t o r of t h i s research. He wishes t o thank the members of the f a c u l t y and f e l l o w graduate students of the Department of M e t a l l u r g y f o r t h e i r continued support and i n t e r e s t i n t h i s work. S p e c i a l thanks are extended t o Mr. R. R i c h t e r for. assistance, w i t h equipment and Mr. R..G. But t e r s f o r t e c h n i c a l advice. The author i s g r a t e f u l f o r f i n a n c i a l , a s s i s t a n c e • p r o v i d e d by the Research C o r p o r a t i o n , New York, the N a t i o n a l Research C o u n c i l of Canada,,and Canadian Western Pipe M i l l s of Port Moody,, B.C. i i i TABLE OF CONTENTS Page I . INTRODUCTION AND REVIEW OF THE LITERATURE ON EMBRITTLEMENT BY LIQUID METALS 1 A. INTRODUCTION 1 B. REVIEW OF THE LITERATURE ON "EMBRITTLEMENT BY LIQUID METALS 2 ( i ) The E f f e c t of L i q u i d Metal on the P l a s t i c Deformation of P o l y c r y s t a l l i n e M a t e r i a l 2 ( i i ) The E f f e c t of L i q u i d Metal on the P l a s t i c Deformation of S i n g l e C r y s t a l s • 4 ( i i i ) Survey of Embrittlement Couples 8 C . THE AIM OF PRESENT INVESTIGATION 9 I I . EXPERIMENTAL PROCEDURE 11 A. - MATERIAL 11 B. SPECIMEN PREPARATION 11 ( i ) Growth of S i n g l e C r y s t a l s 11 ( i i ) Surface Coating of t h e - S i n g l e C r y s t a l s w i t h Mercury 12 C . - TENSILE TESTING - 13 I I I . - EXPERIMENTAL RESULTS 15 A. . WETTING EXPERIMENT 15 ( i ) Zn-Hg System 15 ( i i ) ' W e t t i n g Experiment w i t h P o l y c r y s t a l l i n e Z i n c 16 ( i i i ) Wetting Experiment w i t h S i n g l e C r y s t a l Specimen - . . 16 B. TENSILE TEST OF UNCOATED CRYSTALS C. THE EFFECT OF TIME OF IMMERSION ON THE•WORK HARDENING CHARACTERISTICS 23 i v Table of Contents (cont'd) Page D. THE EFFECT OF EXPOSURE TIME IN AIR AFTER MERCURY COATING ON THE WORK HARDENING CHARACTERISTICS 29 E. THE EFFECT OF PRESTRAIN AND MERCURY COATING ON THE WORK HARDENING CHARACTERISTICS 29 F. THE EFFECT OF MERCURY COATING AND HIGH TEMPERATURE ON THE WORK . HARDENING CHARACTERISTICS . . . . . . 3^ G. • SUMMARY OF RESULTS 37 H. REPRODUCIBILITY OF THE RESULTS . . . 38 IV. METALLOGRAPHIC OBSERVATIONS . 39 V. DISCUSSION k6 A. WETTING CHARACTERISTICS AND DIFFUSION OF MERCURY IN ZINC 46 ( i ) Wetting C h a r a c t e r i s t i c s '. k6 ( i i ) The D i f f u s i o n of Mercury i n Zinc k6 B. THE EFFECT OF MERCURY COATING- ON THE-CRITICAL RESOLVED SHEAR STRESS OF ZINC SINGLE CRYSTALS . . . . . k& ( i ) D i s l o c a t i o n Egress E f f e c t . . . . . . . k$ ( i i ) Surface Drag E f f e c t k$ ( i i i ) Surface Anchoring E f f e c t 51 C. THE EFFECT OF MERCURY COATING ON THE WORK- HARDENING. OF ZINC SINGLE CRYSTAL 52 D. PROPOSED MECHANISM FOR CRACK INITIATION 55 VI. CONCLUSION 59 V I I . APPENDICES 60 A. THERMODYNAMICS OF THE SPREADING' OF LIQUIDS ON SOLID PHASE 60 •B. DISLOCATION PIPE DIFFUSION 62 V Table of Contents (cont'd) Page C. RESULTS OF. TENSILE TEST 65 D. . ESTIMATION OF ERRORS 70 REFERENCES . - 72 v i LIST OF FIGURES Page. F i g . 1. Mounting Apparatus ik F i g . 2. Dimensions of Mounted C r y s t a l Ik l F i g . 3. Hg-Zn System 15 F i g . k. .Weight Gained per U n i t Area of the Surface b y P o l y c r y s t a l l i n e Specimens 17 F i g . 5. Weight Gained p e r U n i t Area of the Surface by'Single C r y s t a l Specimens 18 F i g . 6. The Three Stage Shear S t r e s s - S t r a i n Curve f o r h.c.p. • S i n g l e ' C r y s t a l 20 F i g . 7- Shear S t r e s s - S t r a i n Curves for'Uncoated C r y s t a l s Tested i n Tension a t Room• Temperature 22 F i g . 8. Shear S t r e s s - S t r a i n Curves f o r Coated C r y s t a l s Te.sted i n Tension at Room Temperature (time of immersion i n a i r a f t e r c o a t i n g : 5 mins.) 26 F i g . 9« Shear S t r e s s - S t r a i n Curves f o r Coated.Crystals Tested.in Tension at Room Temperature (time of immersion i n a i r a f t e r c o a t i n g : 10 and 15 mins.) 27 F i g . 10. The E f f e c t of Exposure Time a f t e r Coating-on Fracture S t r a i n 29 F i g . 11. • S h e a r - S t r e s s - S t r a i n Curves f o r P r e s t r a i n e d and Coated C r y s t a l s Tested i n . Tension a t Room Temperature 31 (amount of p r e s t r a i n : 30$ ) F i g . 12. Shear S t r e s s - S t r a i n Curves f o r Prestrained-and Coated C r y s t a l s T ested-in Tension at Room Temperature . .32 (amount of p r e s t r a i n : . 100 and 105$) F i g . 13. -Shear S t r e s s - S t r a i n Curves f o r P r e s t r a i n e d and Coated C r y s t a l s Tested at Room Temperature ' 35 (amount of p r e s t r a i n : 162 and 165$) F i g . Ik. The E f f e c t of P r e s t r a i n and Mercury Coating on "tf'^- Tf'gp • • • 3^ F i g . 15. The E f f e c t of Mercury-Coating and Higher Temperatures on Fracture S t r a i n . . . . . . . 36 F i g . 16. Microphotograph of ZXI-I-3 • • • • kO F i g . 17. Microphotograph of ZXI-N-3 . . .- - . h0 • v i i L i s t of Figures (cont'd) Page F i g . 18. Microphotograph of ZXI-N-2 . . kl F i g . 19. -Microphotograph of ZXI-0-1+ . . . . . . . . . . . 1+1 F i g . 20. -Microphotograph of ZXI-M-2 1+2 F i g . 21. Microphotograph of ZXI-0-3 k2 F i g . 22. Microphotograph of ZXI-V-2 . . 1+3 F i g . 23. Microphotograph o f ZXI-V-1 . . . . 1+3 F i g . 2k. Crack I n i t i a t e d by Coalescence of D i s l o c a t i o n s on M a t r i x B a s a l Plane Propagates along B a s a l Plane i n Twin 1+1+ F i g . 25. Crack I n i t i a t e d a t Kink W a l l 1+5 F i g . 26. Crack I n i t i a t e d at T e n s i l e Kink ,1+5 F i g . 27. Cracks I n i t i a t e d at T e n s i l e Kinks - . . 1+5 F i g . 28. Mercury M i g r a t i o n t o Newly-Exposed B a s a l Plane During-Deformation 1+7 F i g . 29. F i s h e r Single-Ended Source 50 F i g . 30. Schematic P i c t u r e of Fanning Process at Both Ends of the Same S l i p Plane 53 F i g . 31- Geometry of Twin i n Zi n c . 55 F i g . 32. Zener's Model f o r the N u c l e a t i o n of Crack by D i s l o c a t i o n Coalescence as an A l t e r n a t i v e t o S l i p Propagation 56 P i g . 33. Schematic P i c t u r e of Bullough - Gilman - Rozhanskii Model f o r C r a c k ' I n i t i a t i o n i n Zi n c 58 v i i i LIST: OF TABLES ^  Page Table I . Embrittlement Couple 9 Table I I . The Values of Parameters Obtained by-Tensile T e s t i n g Uncoated -. C r y s t a l s 21 Table I I I . The E f f e c t of Immersion-Time on the Work Hardening C h a r a c t e r i s t i c s - .. .. 2k Table IV. The E f f e c t of Exposure Time i n A i r a f t e r Mercury. Coating on Work Hardening. C h a r a c t e r i s t i c s 28 Table V. The E f f e c t of P r e s t r a i n and Mercury Coating on Work Hardening C h a r a c t e r i s t i c s .- . . 31 Table V I . The E f f e c t of Mercury Coating and Preheating on Room Temperature Deformation C h a r a c t e r i s t i c s . . . . . . . . . . . 35 \ - 1 - I INTRODUCTION AND REVIEW OF THE LITERATURE ON EMBRITTLEMENT BY LIQUID METALS A. INTRODUCTION The e f f e c t s of surface environment on the p l a s t i c deformation of m a t e r i a l s have been observed f o r many years. According t o v a r i o u s i n v e s t i g a t i o n s , the m a t e r i a l s i n f l u e n c e d range from stone and g l a s s t o pure metals and a l l o y s i n environments which are e i t h e r gases or l i q u i d s . Many i n v e s t i g a t o r s have attacked t h i s f i e l d under a v a r i e t y of headings such as s t r e s s c o r r o s i o n , hydrogen embrittlement, c o r r o s i o n f a t i g u e , l i q u i d metal c o r r o s i o n and f a t i g u e . There are many s i m i l a r i t i e s evident i n a l l of the t o p i c s j u s t mentioned. However, i n t h i s paper, p a r t i c u l a r a t t e n t i o n w i l l be focussed on those i n v e s t i g a t i o n s r e l a t i n g t o l i q u i d metal embrittlement. The e f f e c t of surface a c t i v e media on the mechanical behavior of ma t e r i a l s has been s t u d i e d e x t e n s i v e l y i n the S o v i e t Union since the e a r l y work of Rehbinder i n 1931. L i q u i d metal embrittlement was considered w i t h i n the broad f i e l d of physicochemical mechanics whereby the surrounding media modify the p h y s i c a l and mechanical p r o p e r t i e s of m a t e r i a l s as a r e s u l t of the formation of adsorbed surface l a y e r s . P o s s i b l e surface a c t i v e media can be s o l i d , l i q u i d or gaseous. The main e f f e c t o f such a l a y e r i s to reduce the stren g t h and hardness of the m a t e r i a l w i t h increased d u c t i l i t y . In c o n s i d e r i n g l i q u i d metal embrittlement, we u s u a l l y observe d r a s t i c decrease i n d u c t i l i t y . A l s o the r o l e of d i s l o c a t i o n can not be over-- 2 - looked because some p l a s t i c deformation always precedes embrittlement by l i q u i d metals. Any d i s l o c a t i o n mechanism f o r crack i n i t i a t i o n presupposes some st a b l e o b s t a c l e s t o the motion of d i s l o c a t i o n s . With p o l y c r y s t a l l i n e m a t e r i a l s , t h i s f u n c t i o n i s u s u a l l y performed by a g r a i n boundary. However i t has been observed t h a t , i n some m a t e r i a l , cracks may be i n i t i a t e d i n the center of 1 2 grains . Studies on s i n g l e c r y s t a l s , p a r t i c u l a r l y cadmium , have provided good evidence t h a t both crack i n i t i a t i o n and propagation can be a s s i s t e d by the presence of a c t i v e l i q u i d metal atoms. Therefore i t i s q u i t e conceivable t h a t l i q u i d metal environments e i t h e r provide a b a r r i e r or s t a b i l i z e some p o t e n t i a l b a r r i e r t o d i s l o c a t i o n movement. B. REVIEW OF THE LITERATURE ON EMBRITTLEMENT BY LIQUID METALS ( i ) The E f f e c t of L i q u i d Metal on the P l a s t i c Deformation of P o l y c r y s t a l l i n e  M a t e r i a l s The l o s s of st r e n g t h and d u c t i l i t y of metals under s t r e s s and i n contact w i t h surface a c t i v e metals has been the subject of many i n v e s t i g a t i o n s . Reported r e s u l t s i n d i c a t e disagreement on the nature of the embrittlement and p r i n c i p a l mechanisms i n v o l v e d r e f l e c t i n g the complexity of the problems r e l a t e d w i t h l i q u i d metal embrittlement. To develop the p i c t u r e t h a t both s t r e s s and l i q u i d metals are necessary c o n j o i n t l y f o r the i n i t i a t i o n of embrittlement, Heyn 3, Rawdon 4, and Moor and B e c k i n s a l e 5 have done experiments w i t h brass wetted by mercury. I t was t h e i r b e l i e f t h a t the simultaneous e f f e c t s of i n t e r n a l s t r e s s e s i n the m a t e r i a l and the p e n e t r a t i o n of mercury deposited a t the g r a i n boundaries of - 3 - the brass caused i n t e r g r a n u l a r c r a c k i n g . I n v e s t i g a t i o n of elevat e d temperature e f f e c t s permitted the use of a wide range of l i q u i d metals i n a d d i t i o n t o mercury. M i l l e r 6 determined the t e n s i l e p r o p e r t i e s of 6o/kO and jo/30 brasses coated w i t h l i q u i d t i n , l e a d , and s o l d e r at temperature up t o 350°C, and found the embrittlement process was s i m i l a r t o t h a t of brass by mercury although h i g h s t r e s s e s were required f o r f r a c t u r e . Recently, Rosenberg and C a d o f f 7 pointed out t h a t the wide v a r i a t i o n i n r e s u l t s were due t o the wide v a r i e t y of experimental programs c a r r i e d out, and focussed i n t e n s i v e a t t e n t i o n t o a d e t a i l e d study of one system, copper a l l o y s , wetted w i t h mercury and mercury base s o l u t i o n s . They came t o f o l l o w i n g c o n clusions: (1) The e l o n g a t i o n of copper i n mercury i s grea t e r than t h a t of the Cu-Zn a l l o y , the l a t t e r being g e n e r a l l y considered a case of embrittlement. (2) The e f f e c t of g r a i n s i z e on y i e l d s t r e n g t h , f r a c t u r e s t r e n g t h , and l o s s of e l o n g a t i o n are t o be noted. The r e l a t i o n s h i p between f r a c t u r e s t r e s s versus g r a i n s i z e , D - 1/ 2 can be r e l a t e d by T f = T 0 f + K_D - 1 /2 l where Tof and K_ are constants o f the system. (3) The f r a c t u r e c h a r a c t e r i s t i c s of copper-aluminum, copper-gold, and copper- germanium a l l o y s wet w i t h mercury are s i m i l a r t o those described f o r the copper-zinc system. The s u s c e p t i b i l i t y t o embrittlement f o r a l l f o u r systems i s i n the order z i n c ^aluminum <germanium ^ g o l d . - k - (k) In copper-zinc system, the r e l a t i o n between the y i e l d s t r e s s " f y s and the g r a i n s i z e D 1/z i s given by -tys = T o y +K2 D* 1^ 2 where Toy and K 2 are constants of system. (5) The w e t t i n g a c t i o n a s s o c i a t e d w i t h changing the l i q u i d - m e t a l composition i s r e i n t r o d u c e d as a s i g n i f i c a n t v a r i a b l e . The concepts of surface energy alone do not appear t o e x p l a i n the wide v a r i a t i o n (an increase i n f r a c t u r e s t r e s s over t h a t obtained i n pure mercury) caused by changes i n the l i q u i d - m e t a l composition. The i n t e r a c t i o n of l i q u i d metal w i t h the s o l i d at the root of the s t a b i l i z e d or advancing crack i s necessary f o r a complete understanding of the problem. (6) The g r a i n s i z e dependence observed i n the p r e s t r a i n experiments i n d i c a t e s t h a t , f o r l a r g e g r a i n samples, the d i s l o c a t i o n p i l e - u p dependence on g r a i n diameter c o n t r o l s the f r a c t u r e and thus there i s g r e a t e r s u s c e p t i  b i l i t y at l a r g e r g r a i n s i z e s . (7) The measurements f o r f r a c t u r e boundaries appear t o be somewhat s c a t t e r e d at f i r s t glance, but c l o s e r i n s p e c t i o n shows that the angle between s l i p planes i n adjacent g r a i n s i s not of major s i g n i f i c a n c e , t h a t only coincidence of s l i p d i r e c t i o n i s necessary f o r the i n h i b i t i o n of mercury p e n e t r a t i o n . ( i i ) The E f f e c t of L i q u i d Metal on the P l a s t i c Deformation of S i n g l e C r y s t a l s Likhtman and Shchukin 3 i n v e s t i g a t e d the e f f e c t of a mercury c o a t i n g on the deformation c h a r a c t e r i s t i c s of z i n c s i n g l e c r y s t a l s . The c r y s t a l s of o r i e n t a t i o n X c = k8° were t e s t e d at room temperature. ( X Q = angle between - 5 - t e n s i l e a x i s and s l i p p l a n e ) . They found t h a t the shear s t r e s s and shear s t r a i n at f r a c t u r e were r e s p e c t i v e l y reduced from l^OKg/cm 2 and 260$ i n a i r t o 20Kg/cm2 and 10$ i n mercury. Shchukin et a l 9 s t u d i e d the o r i e n t a t i o n dependence of normal s t r e s s at f r a c t u r e T^r' and shear s t r a i n a t f r a c t u r e "ftp f o r amalgamated z i n c s i n g l e c r y s t a l s . They e s t a b l i s h e d a c r i t e r i o n f o r the b r i t t l e f r a c t u r e which approximates the constancy of the product of normal . and cleavage s t r e s s r e l a t i v e t o the b a s a l plane of d i f f e r e n t l y o r i e n t e d z i n c monocrystals. This constancy i s expressed by ^ F * F * K " 5 C if I l/2 where K = k ( /L) , k being a dimensionless constant of order u n i t y , G the shear modulus, 2f the s p e c i f i c f r e e energy and L the l e n g t h of s l i p plane. The e f f e c t of temperature and a l l o y l i q u i d metals w i t h v a r i o u s c o n c e n t r a t i o n were i n v e s t i g a t e d by Rehbinder, Kochanova, Bryukhanova and L a b z i n 1 0 " 1 2 . Zinc s i n g l e c r y s t a l s i n the form of 0.5mm wire were coated w i t h t i n , l e a d , a l l o y s o f t i n and l e a d i n v a r i o u s c o n c e n t r a t i o n , and mercury. With t i n - c o a t e d z i n c c r y s t a l s t e s t e d i n t e n s i o n at a temperature below the m e l t i n g p o i n t of the Zn/Sn e u t e c t i c , a s l i g h t increase i n t e n s i l e s t r e n g t h was observed. At higher temperature (350° and i4-00°C) the s t r e n g t h and d u c t i l i t y decreased remarkably. A l s o at the same temperature the nature of f r a c t u r e changed from a d u c t i l e type (uncoated) t o a b r i t t l e type (coated w i t h l i q u i d t i n ) . Both the f r a c t u r e s t r e s s and e l o n g a t i o n were reduced. This - 6 - was considered t o be r e l a t e d w i t h : (1) An increase i n the s o l u b i l i t y of z i n c i n l i q u i d t i n as the temperature was r a i s e d from 350 t o ^ O ' C ; 1 (2) A corresponding decrease i n the i n t e r f a c e surface t e n s i o n . However, Kamdar and Westwood 1 3 pointed out the f a c t t h a t the Russian work d i d not i n c l u d e an i n t e r p r e t a t i o n i n v o l v i n g the e x i s t e n c e or nature of s t a b l e o b s t a c l e s t o the motion of d i s l o c a t i o n s . They p a i d s p e c i a l a t t e n t i o n t o the object of r e v e a l i n g the nature of any s u i t a b l y s t a b l e obstacles t o s l i p . For t h i s purpose, the behavior of amalgamated s i n g l e and asymmetric b i c r y s t a l s were c a r e f u l l y s t u d i e d . They c l a s s i f i e d the s i n g l e c r y s t a l s i n t o three groups based on Xo, the angle between specimen a x i s and the (0001) b a s a l plane. In group I where XQ^'—15°* c r y s t a l s were deformed p r i n c i p a l l y by twinning and both p a r t i a l l y amalgamated and c h e m i c a l l y p o l i s h e d specimens f a i l e d a f t e r only a few percent s t r a i n by secondary cleavage on the (0001) planes of a t w i n . I t was suspected t h a t , under c e r t a i n circumstances, twin boundaries would serve as s t a b l e b a r r i e r s t o d i s l o c a t i o n motion. To examine t h i s hypothesis, they introduced twins i n t o c r y s t a l s of o r i e n t a t i o n X Q = 25° and by g e n t l y i n d e n t i n g the c r y s t a l s w i t h the b l u n t end of a needle. Then oxide f r e e specimens were amalgamated i n the v i c i n i t y of twins and l i g h t l y s t r a i n e d . Cleavage cracks were observed t o i n i t i a t e a t t w i n boundary and t o propagate along b a s a l planes of the m a t r i x c r y s t a l . - 7 - In group I I where 15° ( X 0 ( 70°, p a r t i a l l y amalgamated c r y s t a l s deformed i n a d u c t i l e manner and d i d not f r a c t u r e u n t i l shear s t r e s s e s of the order 600-1000g/mm2 and s t r a i n s of order 12,-250$ were a t t a i n e d . Fracture of both p a r t i a l l y coated and uncoated c r y s t a l s e v e n t u a l l y occurred a f t e r repeated twinning and u s u a l l y by secondary cleavage on the (0001) plane of a tw i n . O c c a s i o n a l l y , amalgamated specimens d i d f r a c t u r e at r e l a t i v e l y low s t r a i n s (20-60$) and examination o f these specimens revealed t h a t , i n a l l i n s t a n c e s , f r a c t u r e had i n i t i a t e d a t k i n k bands which formed i n the v i c i n i t y of the g r i p s during the t e n s i l e t e s t . In group I I I where X 0 ^ 70° > c r y s t a l s were s i g n i f i c a n t l y e m b r i t t l e d by mercury and f r a c t u r e occurred always at a ki n k band formed i n the amalgamated gauge s e c t i o n . They c a r r i e d out f u r t h e r experiments w i t h p a r t i a l l y amalgamated asymmetric b i c r y s t a l s and found t h a t cleavage cracks were i n i t i a t e d at the g r a i n boundary of b i c r y s t a l s , and propagated completely through the c r y s t a l s . T h e i r conclusions can be summarized as f o l l o w s : (1) Adsorption of the l i q u i d metal a t some s t a b l e obstacle t o s l i p i s a necessary c o n d i t i o n of l i q u i d metal embrittlement. Consequently, z i n c s i n g l e c r y s t a l s o r i e n t e d f o r s i n g l e s l i p and t e s t e d i n t e n s i o n are not e m b r i t t l e d unless the l i q u i d metals are adsorbed s p e c i f i c a l l y at k i n k bands formed near the g r i p s during deformation. (2) Experiments w i t h amalgamated b i c r y s t a l s provide convincing support f o r cleavage f r a c t u r e i n zi n c proposed by Likhtman-Shchukin and d e r i v e d from an a n a l y s i s by Gilman. - 8 - The e f f e c t of mercury on the cleavage f r a c t u r e energy of z i n c s i n g l e c r y s t a l s was a l s o i n v e s t i g a t e d by Westwood and KamdariA. They a p p l i e d Obreimov-Oilman cleavage technique i n which p a r t i a l crack was introduced by crack i n i t i a t i n g j i g and prevented from propagating completely through the specimen by the a p p l i c a t i o n of a s m a l l compressive s t r e s s p e r p e n d i c u l a r t o the d i r e c t i o n of propagation. They found the t o t a l energy i n v o l v e d i n the propagation of a crack, 0 can be expressed by the r e l a t i o n 0 -vr* k where 0^ i s the c o e f f i c i e n t of embrittlement which r e l a t e s the energy r e q u i r e d t o separate atoms at crack t i p i n the presence and absence of mercury, i s a dimensionless v a r i a b l e depending upon the degree of p l a s t i c r e l a x a t i o n at the crack t i p and independent of 7^  , and if o i s the t r u e surface energy of the f r a c t u r e plane. I n t h e i r work "0/o_;n(298oK) w a s determined t o be 87 ± 5 erg/cm 2 and ^ Zn-Hg ( 2 9 8°K) t o be 0.61 * 0.12. ( i i i ) Survey of Embrittlement Couples Pertsov and R e h b i n d e r 1 5 have s t u d i e d embrittlement couples w i t h the a i d of b i n a r y phase diagram. They found s e m i e m p i r i c a l r u l e s i n d i c a t i n g whether or not a given molten metal Mi i s s t r o n g l y surface a c t i v e i n regard t o another metal M 2 of higher m e l t i n g p o i n t . T h e i r r e s u l t s can be summarized as f o l l o w s ; (see Table I ) . (1) There i s considerable r e d u c t i o n i n s t r e n g t h and d u c t i l i t y i f metal Mi has a narrow, but f i n i t e , r e g i o n of s o l u b i l i t y i n the s o l i d s t a t e i n the metal M2. - 9 - (2) On the c o n t r a r y , no embrittlement e f f e c t i s normally observed i f t h i s s o l u b i l i t y r e g ion i s very wide or absent a l t o g e t h e r . TABLE I Embrittlement Couple Reduction i n s t r e n g t h of metal under the e f f e c t of a molten metal c o a t i n g No r e d u c t i o n i n s t r e n g t h of metal under the e f f e c t of a molten metal c o a t i n g Metal Studied Metal Coated Metal Studied Metal Coated Cadmium T i n Cadmium Mercury Cadmium Ga l l i u m Lead Mercury Zinc Mercury Copper Mercury Zi n c G a l l i u m Copper T i n Z i n c T i n Copper Zinc T i n Mercury Zi n c Lead T i n G a l l i u m - - Copper Bismuth - - C. THE AIM OF PRESENT INVESTIGATION Although v a r i o u s kinds of experiments on l i q u i d metal embrittlement have been c a r r i e d out t o e s t a b l i s h the exact mechanism and a s s o c i a t e d problems, none of them p a i d s p e c i a l a t t e n t i o n t o the work hardening c h a r a c t e r i s t i c s of s i n g l e c r y s t a l s i n the presence of surface a c t i v e media. - 1 0 - In t h i s present i n v e s t i g a t i o n , an attempt has been made t o e x p l a i n the l i q u i d metal embrittlement i n the context of the present understanding of deformation theory under the f o l l o w i n g experimental schemes. (1) The system s t u d i e d c o n s i s t s o f z i n c s i n g l e c r y s t a l s of f i x e d o r i e n t a t i o n wetted by mercury as a surface a c t i v e metal. (2) The amount of mercury used f o r c o a t i n g and time of immersion of c r y s t a l s i n mercury were f i x e d . (3) C r i t i c a l r e s o l v e d shear s t r e s s T c , work hardening slope i n stage A (0^ ) and stage B ( O g ) , t r a n s i t i o n s t r a i n from stage A t o B , A^_J_^  parameters t o compare the r e s u l t s obtained from d i f f e r e n t experimental c o n d i t i o n s . at which the shear s t r e s s s t r a i n curve f i r s t deviates from l i n e a r i t y because coated specimens under c e r t a i n experiment c o n d i t i o n s f a i l before the f u l l development of stage A making assessment o f the value rCc by e x t r a  p o l a t i n g stage A impossible. f r a c t u r e s t r a i n and f r a c t u r e s t r e s s T x were d e f i n e d as C r i t i c a l r e s o l v e d shear s t r e s s was determined from the s t r e s s - 11 - I I . EXPERIMENTAL PROCEDURE A. MATERIAL The z i n c used i n t h i s experiment was purchased from the Cons o l i d a t e d Mining and Smelting Company L i m i t e d , T r a i l , B.C., Canada. The p u r i t y of the z i n c was 9 9 - 9 9 9 Commercial grade of mercury was t r e a t e d w i t h concentrated mercuric n i t r a t e and o x i d i z e d so t h a t base metal i m p u r i t i e s can be removed. The mercury used i n t h i s experiment was mainly contaminated by z i n c , s o l d e r (specimen mounting a l l o y ) , and aluminum ( g r i p ) . During the o x i d a t i o n , a s i l v e r y f r o t h begins t o form and a g i t a t o r s c o n t i n u a l l y f o r c e the f r o t h through the mass of mercury. The f r o t h darkens and t h i c k e n s to a l a y e r . As the o x i d a t i o n proceeds f u r t h e r , a b l a c k powder forms on the surface and the f r o t h g r a d u a l l y disappears, l e a v i n g a l a y e r of dry, b l a c k powder f l o a t i n g on b r i g h t mercury. Oxidized mercury was f i l t e r e d by mercury f i l t e r which c o n s i s t s of a r e s e r v o i r w i t h discharge aperture at the bottom. Surrounding t h i s aperture i s a r i n g of g o l d , which i s the f i l t e r i n g element. F i n a l l y mercury i s f i l t e r e d by gold adhesion p r i n c i p l e . Conta minated mercury from w e t t i n g of z i n c c r y s t a l s i s p u r i f i e d using the above mentioned method. B. SPECIMEN PREPARATION ( i ) Growth of S i n g l e C r y s t a l s The s i n g l e c r y s t a l s were grown from melt by Bridgman's method. Extruded z i n c w i r e together w i t h seed c r y s t a l was charged i n t o pyrex g l a s s tube which has a cl o s e d sharp t i p at one end. The other end of the pyrex - 12 - mould was connected t o vacuum pump t o evacuate a i r i n i t and sealed o f f t o prevent o x i d a t i o n of z i n c during growth. The furnace used f o r growing c r y s t a l s i s a v e r t i c a l type w i t h Ni-Cr w i r e as heat element. A thermocouple was i n s e r t e d halfway of the furnace body and the temperature was c o n t r o l l e d by WHEELCO type c o n t r o l l e r . The temperature i n the v i c i n i t y o f the thermocouple was k^O"C. The v e r t i c a l t r a v e l l i n g r a t e of the charged mould i n the furnace was 35 mm/hr. A f t e r determining temperature d i s t r i b u t i o n of the furnace, the upper h a l f of the seed c r y s t a l was plac e d at melti n g zone so th a t the melt of p o l y c r y s t a l l i n e z i n c would t u r n i n t o monocrystal as the charge moves down. Four charged pyrex molds were t r e a t e d as a s i n g l e batch by above mentioned technique and as a r e s u l t , four long c r y s t a l s of about kOcm long were obtained at one time. To remove the c r y s t a l s from the mould without i n t r o d u c i n g undesired deformation, the g l a s s mould was d i s s o l v e d i n k&jo HF s o l u t i o n . The t h i n oxide f i l m formed during growth kept c r y s t a l s from a t t a c k i n g by HF s o l u t i o n . B a c k - r e f l e e t i o n Laue X-ray method was a p p l i e d t o determine the o r i e n t a t i o n of the grown c r y s t a l s . The o r i e n t a t i o n of a l l c r y s t a l s used i n t h i s i n v e s t i g a t i o n was X Q = h 6 ° * 3° and 9^ o = ^6° * h°, where X c i s the angle between the specimen a x i s and s l i p plane, a nd^o i - s "the angle between the specimen a x i s and s l i p d i r e c t i o n . This o r i e n t a t i o n i s such t h a t s l i p system operates along (0001) plane i n the d i r e c t i o n o f [1120]. ( i i ) Surface Coating o f the S i n g l e C r y s t a l s w i t h Mercury The specimens were p o l i s h e d by e l e c t r o p o l i s h i n g technique i n the mixture s o l u t i o n o f 25g C r 2 0 3 , 7cc H 2 0 and 133cc Cone. CH 3 C00H. - 13 - On removing oxide f i l m on the surface, the c r y s t a l was mounted i n aluminum g r i p s w i t h s o l d e r . Ordinary s o l d e r i n g f l u x pasted at the end of the c r y s t a l improved w e t t i n g of c r y s t a l s w i t h molten s o l d e r . MICROSTOP covered the exposed solder at the g r i p t o avoid contact between mercury and so l d e r . Then both ends of mounted c r y s t a l were wrapped w i t h polyethylene paper t o reduce the p o s s i b i l i t i e s of e a r l y f a i l u r e r e s u l t i n g from adsoption of mercury at the k i n k that appears f r e q u e n t l y i n the v i c i n i t y of g r i p during deformation. The mounted c r y s t a l w i t h p r o t e c t e d ends was pl a c e d i n a s t a i n l e s s s t e e l j i g h o r i z o n t a l l y and tightened very c a r e f u l l y by u s i n g two arms s t r e t c h e d out of the middle of the j i g . F i n a l l y , the j i g was immersed i n t o f i x e d amount of clean mercury contained i n a p l a s t i c boat, and the time of immersion was measured by stop watch. F i g . 1 shows the mounting apparatus and s t a i n l e s s s t e e l j i g which holds mounted specimen. The dimensions of a mounted specimen are shown i n Figure 2 . C. TENSILE TESTING A screw d r i v e n INSTRON t e n s i l e t e s t i n g machine was used f o r the' t e s t . The u n i v e r s a l g r i p p i n g heads were mounted below the cross head so th a t water bath can be attached i n the hi g h temperature t e s t . The gimbals g r i p s which have two r o t a t i o n a l a x i s were used t o achieve quick and smooth alignment of specimen t o the t e n s i o n a x i s . The s t r a i n r a t e and chart speed were f i x e d as 0.1"/min and 1.0"/min r e s p e c t i v e l y . The t e n s i l e t e s t r e s u l t s were recorded by autographic recorder i n the form of l o a d - e l o n g a t i o n curve. CT and C c e l l were used and before proceeding every t e s t , the lo a d system was c a l i b r a t e d t o o b t a i n c o r r e c t l o a d a p p l i e d t o specimens. - Ik F i g . 1. Mounting Apparatus and J i g . GRIP 1.0 2.5 3,2 0^32 SPECIMEN E p 1,25 L_ 0,8 POLYETHYLENE PAPER F i g . 2 . Dimensions of Mounted C r y s t a l . ( U n i t : cm) - 15 - I I I . EXPERIMENTAL RESULTS A. WETTING EXPERIMENT ( i ) Zn-Hg System The phase diagram of Zn-Hg system determined by E.A. Anderson i s shown i n F i g . Hg-Zn Merrury-Zi i ic B Y E . A . ANDERSON* 1 6 500 400 300 200 100 0 -100 Atomic Percentage Mercury io 20 30 AO 50 60 70 SO 90 • i 1 •MI—n L 1 a +1 - 1 1 1 - 1 1 p  _____ > r*a- a + f ft - its " 9 9 S t 6~ Z 600 BOO Boiling 400 200 -38.9' Zn 10 20 30 40 50 60 70 80 90 Hg Weight Percentage Mercury F i g . 3. Hg-Zn System (from Metals Handbook) The s o l u b i l i t y of mercury i n s o l i d z i n c has not been e s t a b l i s h e d a c c u r a t e l y , but i s probably l e s s than 1$ at room temperature. According t o Von S i m s o n 1 7 the |3 phase i s hexagonal w i t h an a x i a l r a t i o of 2 . 0 1 . The c r y s t a l s t r u c t u r e of "Zf phase, s t a b l e o nly below room temperature, has not been determined. - 16 - ( i l ) Wetting Experiment w i t h P o l y c r y s t a l l i n e Z i n c Mercury i s s t r o n g l y surface a c t i v e w i t h respect t o z i n c . As a f i r s t step t o e s t a b l i s h the r e l a t i o n a p p l y i n g t o the w e t t i n g of mercury over the surface of z i n c , two groups of p o l y c r y s t a l l i n e z i n c specimens w i t h d i f f e r e n t g r a i n s i z e were prepared by e x t r u s i o n a t two d i f f e r e n t temperatures. Each specimen of the same group had the same dimension. On p o l i s h i n g the s u r f a c e , each specimen was wetted i n lOcc c l e a n mercury and time of immersion was recorded by stop watch.' The weight gained per u n i t surface area of the specimen was determined by t a k i n g the weight d i f f e r e n c e between wetted and unwetted specimen and d i v i d i n g i t by t o t a l surface area. The r e s u l t i s given i n F i g . k. The specimens of sm a l l g r a i n s i z e (90yCt) revealed a maximum at 130 sees w i t h the weight gained, 1.05mg/cm2. On the other hand, the maximum weight gained by specimens of l a r g e r g r a i n s i z e (190>o) was s h i f t e d t o l e f t w i t h the value of 2.66mg/cm2 at 90 sees. The occurrence of maxima i n weight gained vs time o f immersion curve i n d i c a t e s the evidence of counter d i f f u s i o n between z i n c and mercury. A l s o the maxima revealed a t d i f f e r e n t immersion time i m p l i e s the importance of g r a i n boundary d i f f u s i o n . ( i i i ) Wetting Experiment w i t h S i n g l e C r y s t a l Specimen Two groups of s i n g l e c r y s t a l s grown by d i f f e r e n t growth r a t e were used i n t h i s experiment. The clea n and oxide f r e e surface was obtained by e l e c t r i c p o l i s h i n g i n the mixture s o l u t i o n of 25g C r 2 0 3 , 7 C CH_0 and 133cc cone. C H 3 C O O H w i t h 18 v o l t . Then the c r y s t a l s were coated i n 50cc - 18 - F i g . 5. Weight Gained per U n i t Area of the Surface by- S i n g l e C r y s t a l Specimens. - 19 - clean mercury and the weight gained per u n i t surface area determined by the same technique used f o r p o l y c r y s t a l l i n e specimens. The r e s u l t i s shown i n F i g . 5 . As the case of p o l y c r y s t a l l i n e specimens, weight gained per u n i t surface area vs time of immersion curves a l s o revealed maxima. The idea of preparing two groups of monocrystals by the d i f f e r e n t growth r a t e was t o detect the e f f e c t of d e n s i t y of s t r u c t u r a l defect (vacancy or d i s l o c a t i o n ) on w e t t i n g c h a r a c t e r i s t i c s . The discrepancy of maxima between these two groups of c r y s t a l s , however, appears t o be due t o the d i f f e r e n c e of surface c o n d i t i o n (degree of micro r e l i e f ) and not that of d e n s i t y of s t r u c t u r a l d e f e c t s . B. TENSILE TEST OF UNCOATED CRYSTALS The shear s t r e s s - s t r a i n curve produced by the s l i p on h.c.p. metal i s i l l u s t r a t e d by the w e l l known three stage i n F i g . 6. I n order t o i n v e s t i g a t e the e f f e c t of mercury c o a t i n g on the deformation c h a r a c t e r i s t i c s of z i n c s i n g l e c r y s t a l s , the f o l l o w i n g parameters were defined and s t u d i e d . (1) The c r i t i c a l r e s o l v e d shear s t r e s s ' f c> determined from the s t r e s s at which the shear s t r e s s - s t r a i n curve f i r s t deviates from l i n e a r i t y . (2) The t r a n s i t i o n s t r a i n Y A g> from stage A t o stage B determined by the s t r a i n at which the l i n e a r stage A ends. (3) The work hardening slopes and Qg which were measured from the slopes of the shear s t r e s s - s t r a i n curve i n stage A and B. (k) The f r a c t u r e s t r e s s 'Xt and s t r a i n "tfi a t which the specimen f a i l e d . - 2.1 - Three uncoated specimens were t e s t e d a r room temperature to obta i n standard values of above mentioned parameters and then compared w i t h the r e s u l t s of subsequent experiments. The resolved shear s t r e s s - s h e a r s t r a i n curves were obtained from the load - e l o n g a t i o n chart u s i n g the formula given by B o a s 1 8 . The r e l a t i o n s are given by T= l s i n X C io ( . / A f - S i n ^ Q ) . . . . - 5 A 1 ^ V K±Q> and where P i s t e n s i l e l o a d , A i s o r i g i n a l area of cross s e c t i o n , 1D i s i n i t i a l gauge l e n g t h , 1 i s gauge l e n g t h a f t e r deformation, X_ and have the same meaning as defined before. F i g . 7 shows r e s o l v e d shear s t r e s s - s t r a i n curves of uncoated c r y s t a l s f o r the t e n s i l e t e s t performed at room temperature w i t h a s t r a i n r a t e of 0.1"/min. The r e s u l t s are summarized i n Table I I . TABLE I I The values of parameters obtained by t e n s i l e t e s t of uncoated c r y s t a l s Spec. f c(Kg/cm 2) No, Q A(Kg / c m 2/i.s.) 1A-B(*) TA_B(Kg/cm2) 0 E ( K g / c m 2 / u < S o ) M i ) Tt( Kg/cm 2) zxs - x - i 1.71 zxs-c-3 1.69 ZX3-K-2 I.76 10.3 11.2 10.5 150 135 19 20 19 62.5 63.0 80.0 413 356 101 103 80 C. THE EFFECT OF TIME OF IMMERSION ON THE WORK HARDENING CHARACTERISTICS A s e r i e s o f experiments were done t o i n v e s t i g a t e the e f f e c t of immersion time on the work hardening c h a r a c t e r i s t i c s under the premise t h a t amount of mercury picked up by z i n c monocrystals increases w i t h immersion time. In t h i s s e r i e s of experiments, both ends of the c r y s t a l near g r i p s were not p r o t e c t e d and during the immersion, they were a l s o coated by mercury. The amount of mercury used was 50cc. The exposure time between w e t t i n g and t e s t i n g was f i x e d f o r 5 mins. Then, the coated specimens were t e s t e d at room temperature w i t h a s t r a i n r a t e of 0.1"/min. More than h a l f of the specimens f a i l e d at k i n k bands i n the v i c i n i t y of g r i p s . The mounting a l l o y ( s o l d e r ) exposed t o mercury during c o a t i n g adsorbed more mercury than c e n t r a l part of the c r y s t a l so that k i n k s formed near the g r i p s were i n more favourable c o n d i t i o n f o r heavy mercury c o a t i n g . Table I I I shows the t e s t i n g r e s u l t s when time of immersion changed from 2 sees t o 8 sees. F r a c t u r e s t r e s s and s t r a i n were not i n c l u d e d i n the t a b l e because unexpected e a r l y f a i l u r e of specimens at g r i p s revealed wide spreading r e s u l t s which have no value of comparison. The r e s u l t s can be summarized as f o l l o w s . (1) C r i t i c a l r e s o l v e d shear s t r e s s was increased by mercury c o a t i n g and dependent on time of immersion. (2) Work hardening slope i n stage A was increased compared t o the uncoated c r y s t a l s , but the increase was almost i n s e n s i t i v e t o time of immersion. (3) T r a n s i t i o n s t r a i n from stage A t o B had a decreasing tendency w i t h time of immersion. (k) The change of t r a n s i t i o n s t r e s s ''£''A-B 'was q u i t e random. (5) Work hardening slope i n stage B increased s l i g h t l y but e a r l y f a i l u r e of specimens w i t h an immersion time beyond 8 sees made i t obscure t o prove. - 24 - TABLE I I I The E f f e c t of Immersion Time on the Work Hardening C h a r a c t e r i s t i c s Specimen No. T c (Kg/cm 2) 9A(Kg/cm2/u.s.) *A-B(*) ?A_B(Kg/cm2) 0B(Kg/cm2^.s.) Time of Immersion (sees) ZXS-W-3 1.76 10.0 125 16 86 2 ZXS-H-2 1.25 12.2 125 23 70 2 ZNX-F-2 1.8 12.0 115 20 50 2 ZXS-J-1 1.77 10.0 115 16 75 4 ZXS-G-3 1.79 13.0 125 20 80 4 ZXII-E-1 l . 8 l 8.5 125 13 60 4 ZXS-W-2 1.83 11.4 110 16 - 6 ZXS-G-1 1.84 11.8 115 19 - 6 ZX0-E-2 1.82 11.0 125 17 85 6 ZXS-U-1 1.96 12.3 100 15 - 8 ZXS-D-1 2.0 12.0 - - - 8 ZXII-B-2 2.03 - - - - 8 D. THE EFFECT OF EXPOSURE TIME IN AIR AFTER MERCURY COATING ON THE WORK HARDENING CHARACTERISTICS. D i f f u s i o n i s a time dependent process. Therefore exposure of coated specimens i n a i r f o r a c e r t a i n time should i n t e n s i f y the e f f e c t of embrittlement i f the embrittlement i s due t o the d i f f u s e d surface a c t i v e l i q u i d metal i n t o the c r y s t a l s . - 25 - In t h i s experiment, hoth ends of the specimen near g r i p s were pr o t e c t e d by wrapping them w i t h polyethylene paper. At the same time, mounting a l l o y exposed at g r i p s was covered by MICROSTOP t o keep the a l l o y from mercury. Then, the specimens were coated w i t h mercury by immersing them i n t o 50cc clean mercury f o r 8 sees and t e s t e d at room temperature w i t h a s t r a i n r a t e of 0.1"/min„ F i g . 8-9 show the r e s u l t s when exposure time was increased g r a d u a l l y from 5 mins t o 15 mins'. The e f f e c t of exposure time i n a i r a f t e r c o a t i n g on the work hardening c h a r a c t e r i s t i c s is given i n Table TV-. The r e s u l t s can be summarized as f o l l o w s : (1) The mercury c o a t i n g increased "X c compared t o t h a t of uncoated specimens and the increase was dependent on time of exposure i n a i r a f t e r c o a t i n g . (2) Work hardening slope i n stage A was increased compared t o uncoated c r y s t a l s w i t h decreasing tendency t o a value s i m i l a r t o t h a t of uncoated crystals as the time of exposure i n c r e a s e s . (3) T r a n s i t i o n s t r a i n from stage A t o B was remarkably decreased w i t h time of exposure and the stage B was e l i m i n a t e d a f t e r 30 mins. exposure in a i r . F i g . 10 shows the r e d u c t i o n of f r a c t u r e s t r a i n w i t h the time of exposure i n a i r . (k) The t r a n s i t i o n s t r e s s T A _ g was i n the neighbourhood of that of uncoated specimen. However these values were g e n e r a l l y higher than the corresponding stresses of the same amount of s t r a i n i n uncoated specimens. (5) Work hardening slope i n stage B was a l s o increased compared to uncoated c r y s t a l s . 0 0,5 1,0 1,5 2,0 2,5 3,0 35 SHEAR STRAIN Y F i g . 8. Shear S t r e s s - S t r a i n Curves f o r Coated C r y s t a l s Tested i n Tension o at Room Temperature (Time of Exposure i n A i r a f t e r Coating: 5 mins) , 0 0,5 1,0 1,5 2,0 2,5 3,0 SHEAR STRAIN * F i g , 9. Shear S t r e s s - S t r a i n Curves f o r Coated C r y s t a l s Tested i n Tension at Room Temperature (Time of Exposure i n A i r a f t e r Coating: 10 and 15 mins. TABLE IV The E f f e c t of Exposure Time i n A i r a f t e r Mercury Coat i n g on Work Hardening C h a r a c t e r i s t i c s Specimen No. T c (Kg/cm 2) 6 A(kg/cm 2/u.s.) tfA-B(*) f A _ B ( K g / c m 2 ) f3B(Kg/cm2u.s.) If (Kg/cm 2) Time of Exposure (min) ZXI-N-3 2.00 13.3 110 17 95 104.1 304 5 ZXS-F-3 1.99 17.2 95 21 75 100.0 254 5 ZXS-F-2 1.95 17.2 100 22 70 97-6 267 5 ZXS-N-2 2.03 12.0 100 16 95 97-0 267 10 ZXI-0-4 2.03 16.0 90 21 70 59-0 173 15 ZXI-0-2 2.06 17.1 80 21 65 61.6 179 15 ZXI-M-3 2.07 12.6 - - - 13.2 62 30 ZXI-M-2 2.12 14.3 - - - 14.5 72 30 ZXI-L-4 2.12 13.6 - - - 8.7 33 60 ZXI-0-3 2.11 9.7 - --- - 6.1 38 60 - 29 0 10 2 0 3 0 4 0 5 0 6 0 7 0 EXPOSURE TIME (MIN) F i g . 10. The E f f e c t of Exposure Time a f t e r Coating on Fracture S t r a i n . E. THE EFFECT OF PRESTRAIN AND MERCURY COATING ON THE WORK HARDENING CHARACTERISTICS. The s t r u c t u r a l d e f e c t s increase as deformation proceeds. I f the i n t e r a c t i o n s between s t r u c t u r a l defects and d i f f u s e d surface a c t i v e l i q u i d metal causes the embrittlement, the amount of p r e s t r a i n should modify the work hardening c h a r a c t e r i s t i c s of z i n c monocrystal coated w i t h mercury. A f t e r clean c r y s t a l s were p r e s t r a i n e d up t o c e r t a i n amount of shear s t r a i n , they were removed from INSTRON and both ends of c r y s t a l s were protected - 30 - before mercury c o a t i n g . Then those specimens w i t h p r o t e c t e d ends were immersed i n 50cc mercury f o r 8 sees. Test was resumed a f t e r 10 min wrapping and subsequent 5)mm exposure i n a i r . F i g . 11-13 show the shear s t r e s s - s t r a i n curve w i t h g r a d u a l l y increased amount of p r e s t r a i n . The e f f e c t of p r e s t r a i n and mercury c o a t i n g on deformation parameters i s given i n Table V. The r e s u l t s can be summarized as f o l l o w s : (1) C r i t i c a l r e s o l v e d shear s t r e s s , T" , work hardening slope i n stage A, 0^ and t r a n s i t i o n s t r a i n "2^-15 were not a f f e c t e d since the t e s t s were performed under the same c o n d i t i o n s as those of uncoated c r y s t a l s . (2) P r e s t r a i n and mercury c o a t i n g a f f e c t e d the amount of e l o n g a t i o n markedly. I f 7f stands f o r the amount of p r e s t r a i n , the r e s u l t s show t h a t if „- "3V " ps r > f p S decreases w i t h p r e s t r a i n . The change of If r - if was not s i g n i f i c a n t up t o 100$ p r e s t r a i n but a f t e r t h a t dropped d r a s t i c a l l y . This r e l a t i o n i s shown i n F i g . Ik. - 31 - 0 0,2 0,4 0,6 0,8 1,0 SHEAR STRAIN F i g . 11. Shear S t r e s s - S t r a i n Curves f o r P r e s t r a i n e d and Coated C r y s t a l s Tested i n Tension a t Room Temperature. TABLE V. The E f f e c t o f p r e s t r a i n and Mercury Coating on Work Hardening C h a r a c t e r i s t i c s Specimen No. T C (Kg/cm 2) ©A(Kg/cm2/u.s.) TTA-B(*) T A_ B(Kg/cm 2) >Xf (Kg/cm 2) Amount($) of P r e s t r a i n ZXS-D-3 1.81 10.0 - - 16.2 81 30 ZXS-D-2 1.69 10.3 - - 16.3 91 30 ZXI-P-2 1.67 11.0 - - 19.2 151 100 ZXS-L-2 1.78 13.0 - - 26.2 153 105 ZXI-P-4 1.63 10.0 125 17.5 40.8 184 162 ZXI-P-3 I.65 10.0 i4o 18.0 37-7 191 165 40 O Z X I — P-2 SHEAR STRAIN F i g . 12. Shear S t r e s s - S t r a i n Curves f o r P r e s t r a i n e d and Coated C r y s t a l s Tested i n Tension at Room Temperature. ro SHEAR STRAIN TT F i g . 13. Shear S t r e s s - S t r a i n Curves f o r P r e s t r a i n e d and Coated C r y s t a l s Tested i n Tension a t Room Temperatures. 1 0 2 0 6 0 1 0 0 1 4 0 180 AMOUNT OF P R E S T R A I N Tf_ P ( % ) F i g . Ik. The E f f e c t of P r e s t r a i n and Mercury Coating ° n * f " ^ s p F. THE EFFECT OF MERCURY COATING AND HIGH TEMPERATURE ON THE WORK HARDENING CHARACTERISTICS. The importance of surface and l a t t i c e d i f f u s i o n i s evident from the experiments of exposure time and i t has become valuable t o e s t a b l i s h the e f f e c t of higher temperature. D i f f u s i o n processes w i l l be a c c e l e r a t e d at higher temperature and more d r a s t i c embrittlement should be r e s u l t e d . In order t o assess the e f f e c t of mercury c o a t i n g and higher - 35 - temperature on the work hardening c h a r a c t e r i s t i c s of z i n c monocrystals, the f o l l o w i n g experimental procedures were i n v o l v e d . The specimens w i t h p r o t e c t e d ends were coated w i t h mercury by immersing them i n t o 50cc cle a n mercury f o r 8 sees. A f t e r 5 mins exposure i n a i r , the coated specimen was brought t o INSTRON and hot water bath was placed around the specimen. The water bath was heated by v e r t i c a l type immersion heater by c o n t r o l l i n g the input power w i t h a v a r i a c . The temperature was measured w i t h mercury thermometer every three minutes. The temperature v a r i a t i o n was n e g l i g i b l e c o n s i d e r i n g short time of t e s t i n g r e s u l t i n g from e a r l y f a i l u r e of specimens. ( T = t° ± 1°). Coated specimens were h e l d at d e s i r e d h i g h temperature f o r 5 mins and then hot water bath was rep l a c e d by c o l d water bath t o c o o l the specimens down t o room temperature again. Then the specimens were p u l l e d by INSTRON w i t h a s t r a i n r a t e of 0.1"/min. The e f f e c t of mercury c o a t i n g and higher temperature on the work hardening c h a r a c t e r i s t i c s i s given i n Table V I . TABLE VI The E f f e c t of Mercury Coating and Preheating on Room Temperature Deformation C h a r a c t e r i s t i c s Specimen No. r c(Kg/cm 2) 0A(Kg/cm2/u.s.) *A-B(*) 0 B (Kg/cm 2 As.) r f(Kg ycm 2) rf($) Preheat Temp. °C ZXI-V-2 2.09 12.0 - - 13.4 85.7 50 ZXI-V-3 2.20 11.0 - - 13.2 89.7 50 ZXI-W-3 2.30 15.7 - - 7-5 30.0 75 ZXI-V-1 2.24 13.8 - - 9.3 44.0 75 ZXI-Y-3 2.52 - - - 4.6 6.7 95 ZXI-Y-2 2.46 - - - 5-5 9.8 95 - 36 - The r e s u l t s can be summarized as f o l l o w s : (1) The stage B was completely e l i m i n a t e d i n these, experiments i n d i c a t i n g severe embrittlement e f f e c t . C r i t i c a l shear s t r e s s ^ was increased as the temperature in c r e a s e d . (2) The f r a c t u r e s t r e s s and s t r a i n were decreased w i t h the temperature. F i g . 15 shows the e f f e c t of mercury c o a t i n g and h i g h temperature on f r a c t u r e s t r a i n . (3) There was a tendency such t h a t increases as the heat i n g temperature increased. However, the e a r l i e r f a i l u r e s resulting from 5 min. h o l d i n g at 95°C e l i m i n a t e d the s u f f i c i e n t appearance of stage A making assessment of the r e s u l t d i f f i c u l t . 20 40 TEMPERATURE 60 F i g . 15. The E f f e c t of Mercury Coating and Higher Temperatures on Fracture S t r a i n . - 37 - SUMMARY OF RESULTS The weight gained vs immersion time curves obtained from mercury c o a t i n g experiments show maxima i n both p o l y c r y s t a l l i n e and monocrystal specimens. This i m p l i e s the evidence of high counter d i f f u s i o n between z i n c and mercury when they are i n contact w i t h each other. In non-coated c r y s t a l s , the c r i t i c a l r e s o l v e d shear s t r e s s i s 1.72Kg/cm2 and — = 3'05 x 10 i s observed f o r the c r y s t a l o r i e n t a t i o n of X 0 = 46 * 3° and9\_ = 46 * 4° . The r e l a t i o n between 0 A and QB i s Qg = 60 A. ( XQ. = 1 - 8 Kg/cm 2 by J i l l s o n 1 9 ) . The mercury c o a t i n g increases c r i t i c a l r e s o l v e d shear s t r e s s ( T c = 1.99Kg/cm2 f o r 8 sees immersion and 5 mins exposure time i n a i r ) and the increase i s dependent of exposure time i n a i r a f t e r c o a t i n g . The work hardening slopes (0 A and ©g) are increased by mercury c o a t i n g and exposure i n a i r before t e s t i n g . Under the same experimental c o n d i t i o n s , t r a n s i t i o n s t r a i n ^ B i s decreased remarkably and the stage B i s e l i m i n a t e d a f t e r 30 mins exposure i n a i r . A l s o f r a c t u r e s t r e s s and s t r a i n are decreased w i t h exposure time i n a i r . The p r e s t r a i n and mercury c o a t i n g cause the e a r l i e r f a i l u r e of c r y s t a l s . The r e d u c t i o n of if ~- If ( = amount of p r e s t r a i n ) i s not s i g n i f i c a n t i sp sp up t o 100$ p r e s t r a i n and a f t e r t h a t drops d r a s t i c a l l y . When coated c r y s t a l s are t r e a t e d a t el e v a t e d temperatures, increased c r i t i c a l r e s o l v e d shear s t r e s s i s observed. A l s o h i g h temperature treatment e l i m i n a t e s stage B, and the f r a c t u r e s t r e s s and s t r a i n are reduced as the heating temperature i n c r e a s e s . H. REPRODUCIBILITY OF RESULTS T y p i c a l of experiments w i t h s i n g l e c r y s t a l s , the present r e s u l t s showed a s c a t t e r of * 1 5 $ i n most of the measured parameters. A c c o r d i n g l y , a minimum of two specimens were t e s t e d under given experimental c o n d i t i o n s , and the r e s u l t s quoted f o r each c o n d i t i o n are the a r i t h m e t i c mean of a l l t e s t s . - 39 - IV. METALLOGRAPHIC OBSERVATIONS An attempt has been made t o observe the s l i p markings of mercury- coated c r y s t a l s which were deformed under v a r i o u s experimental c o n d i t i o n s . F i g . 16 shows the s l i p l i n e s of an uncoated c r y s t a l deformed at room temperature. Wide deformation twin bands are observed. The wavy c h a r a c t e r i s t i c s of s l i p l i n e s are the evidence of dynamic recovery during the deformation r e s u l t i n g from the climb of edge d i s l o c a t i o n s . Small humps, which are t e n s i l e k i n k "embryos", are observed as at A i n F i g . 16. The causes of these humps may be e i t h e r the s t r e s s concentration on p i t s and trapped oxide or non-uniform d i s t r i b u t i o n of t e n s i l e s t r e s s across s l i p planes. F i g . 17-21 show the surface of deformed c r y s t a l s coated w i t h mercury when time of exposure i n a i r a f t e r c o a t i n g increases from 5 mins. t o 60 mins. At the beginning, the s i z e and number of embryos increases w i t h exposure time u n t i l the time reaches 15 mins. A f t e r t h a t we observe fewer and s m a l l e r embryos on the surface of deformed c r y s t a l s . This behaviour i s understandable since t e n s i l e k i n k embryos should occur a f t e r s u b s t a n t i a l s t r a i n , and the reduced d u c t i l i t y t h a t r e s u l t s from long exposure t o mercury l i m i t s t h e i r formation. F i g . 22-23 show the deformation markings of coated c r y s t a l s t e s t e d at room temperature a f t e r they were t r e a t e d a t elev a t e d temperature (50°C and 75°C). We observe w e l l developed embryos on the surface of the c r y s t a l which was t r e a t e d at the lower temperature. This c r y s t a l has a f a i r amount of d u c t i l i t y . However, F i g . 16. ZXI-I - 3 x 230 (Uncoated and Tested at Room Temperature). F i g . 17. ZXI-N-3 x 230 (Coated and Tested at Room Temperature • Time of Exposure i n A i r ; 5 mins.) - kl - F i g . 18. ZXI-N-2 x 230 (Coated and Tested at Room Temperature. Time of Exposure i n A i r : 10 mins.) F i g . 19. ZXI - 0 - 4 x 230 (Coated and Tested a t Room Temperature. Time of Exposure i n A i r : 15 mins.) - 1+2 - Fig. 20. ZXI-M-2 x 230 (Coated and Tested at Room Temperature. Time of Exposure in A i r : 30 mins.) Fig. 21. ZXI-0-3 x230 (Coated and Tested at Room Temperature. Time of Exposure in A i r : 60 mins.) - 43 - F i g . 22. ZXI-V-2 x 230 (Coated, 5 min. Exposure i n A i r , 5 min. i n 50°C Bath and Quench t o Room Temperature Room Temperature Test.) F i g . 23. ZXI-V-1 x 230 (Coated, 5 min. Exposure i n A i r , 5 min. i n 75°C Bath and Quench t o Room Temperature. Room Temperature Test.) - kk the r e d u c t i o n of d u c t i l i t y due t o the higher temperature treatment e l i m i n a t e s the formation of embryos compared t o lower temperature t r e a t e d one. Fracture surfaces were a l s o c a r e f u l l y examined under the microscope to detect any evidences of crack i n i t i a t i o n and propagation. F i g . 2k shows the i n i t i a t i o n and propagation o f crack developed i n the uncoated c r y s t a l . A crack was i n i t i a t e d on (0001) matrix and propagated along (0001) twin . F i g . 25-27 show cracks f o r coated c r y s t a l s which were i n i t i a t e d a t k i n k bands and propagated along b a s a l plane. Relevant mechanisms w i l l be considered i n the d i s c u s s i o n p a r t . F i g . 2k. Crack I n i t i a t e d by Coalescence of D i s l o c a t i o n s on M a t r i x Basal Plane Propagates along B a s a l Plane i n Twin x 230. Fig. 26. Crack Initiated at Tensile Kink. Fig. 27. Cracks Initiated at Tensile Kinks. - 46 - V. DISCUSSION A. WETTING CHARACTERISTICS AND DIFFUSION OF MERCURY IN ZINC Since the r e d u c t i o n of the mechanical s t r e n g t h and p l a s t i c i t y of z i n c monocrystals r e s u l t s from mercury c o a t i n g , i t has become necessary t o pay a t t e n t i o n t o the r o l e played by w e t t i n g and d i f f u s i o n . ( i ) Wetting C h a r a c t e r i s t i c s As a primary guide from the thermodynamics of the w e t t i n g of s o l i d surfaces by l i q u i d , we derive t h a t a necessary c o n d i t i o n f o r spreading i s r s > -3L 7 where if g i s the surface energy of s o l i d and }f*^ i s that of l i q u i d (see Appendix I ) . There i s sizeable d i f f e r e n c e of surface energy between mercury and z i n c (476 ergs/cm 2 f o r Hg 2° and 859 ergs/cm 2 f o r z i n c 2 1 ) , which s a t i s f i e s the c o n d i t i o n of w e t t i n g . ( i i ) The D i f f u s i o n o f Mercury i n Zinc The weight gained vs time of immersion curve f o r p o l y c r y s t a l l i n e specimens, when they are immersed i n t o f i x e d amount of mercury, i s q u i t e d i f f e r e n t from t h a t of monocrystals. This i m p l i e s t h a t s t r u c t u r a l d e fects p l a y important r o l e s i n d i f f u s i o n . The weight gained vs time of immersion curves f o r both p o l y c r y s t a l l i n e and monocrystal specimen have revealed maxima i n d i c a t i n g evident counter d i f f u s i o n between mercury and z i n c . At f i r s t the weight gained increased as the time of immersion up t o the maximum p o i n t . During t h i s p e r i o d , the weight gained i s l a r g e r than the l o s s of z i n c r e s u l t i n g from c o u n t e r d i f f u s i o n i n t o mercury. A f t e r the maximum, the l o s s of z i n c i n t o the mercury predominates over the weight gained. Considering the d e n s i t y d i f f e r e n c e between mercury and - 4? - z i n c , the occurrence of maxima i n w e t t i n g experiments proves the f a c t t h a t the d i f f u s i o n of z i n c i n t o mercury appears to be very f a s t . The w e t t i n g experiments w i t h s i n g l e c r y s t a l s have a l s o revealed maxima. However, the maxima occurred at e a r l i e r times of immersion than t h a t of p o l y c r y s t a l l i n e specimen. Various attempts designed t o e x p l a i n the d i f f e r e n c e s i n weight gained and maxima times were not s u c c e s s f u l because of the complicated v a r i a b l e s involved ( g r a i n boundary, concentration of s t r u c t u r a l defects and degree of micro r e l i e f e t c . ) . During the t e n s i l e deformation, microscopic surface steps w i l l appear on the surface of c r y s t a l due t o the s l i p r e v e a l i n g new surface of b a s a l planes. Mercury coated over the surface of c r y s t a l s w i l l migrate on the newly exposed b a s a l plane steps t o reduce the o v e r a l l surface energy (see F i g . 28). (a) (b) (c) F i g . 28. Mercury M i g r a t i o n t o Newly Exposed B a s a l Plane During Deformation, (a) Uniform Coating before Test (b) Exposure of New B a s a l Plane Free from Mercury (c) Mercury M i g r a t i o n t o Newly Exposed B a s a l Plane by Surface D i f f u s i o n . - 48 - This migration i s achieved by surface d i f f u s i o n . Pleteneva and Fedoseeva determined the c o e f f i c i e n t of surface d i f f u s i o n of mercury on z i n c by measuring the r a t e of moving f r o n t of mercury on the surface of v e r t i c a l l y clamped z i n c specimen. This measurement s a t i s f i e d a d i f f u s i o n a l r e l a t i o n i n which the height of mercury r i s e was d i r e c t l y p r o p o r t i o n a l t o the square root of the time. The determined value i s 2.48 x 1 0 2 cm 2/sec at 20°C which i s much f a s t e r than the c o e f f i c i e n t of bulk d i f f u s i o n i n z i n c (0.2.3 x 1 0 " 1 1 cm 2/sec at 20°C). In l a t t i c e d i f f u s i o n , s t r u c t u r a l d e f e c t s , ( d i s l o c a t i o n and sub-boundary) p l a y important r o l e . L o v e 2 3 has proposed an adequate model f o r d i s l o c a t i o n pipe d i f f u s i o n i n which d i f f u s i o n occurs along the l i n e of vacant s i t e s l y i n g adjacent t o the edge of e x t r a i n s e r t e d plane i n an edge d i s l o c a t i o n (see Appendix I I ) . Therefore mercury atoms coated over the surface w i l l d i f f u s e through d i s l o c a t i o n p i p e s . As the deformation proceeds more s t r u c t u r a l d e f e c t s can he evolved and enhanced d i s l o c a t i o n pipe d i f f u s i o n i s expected. B. THE EFFECT OF MERCURY COATING- ON THE CRITICAL RESOLVED SHEAR STRESS OF ZINC SINGLE CRYSTAL In c o n s i d e r i n g the cause of increased c r i t i c a l r e s o l v e d shear s t r e s s of amalgamated c r y s t a l s , the f o l l o w i n g three e f f e c t s are r e l e v a n t subjects t o be discussed. ( i ) D i s l o c a t i o n egress e f f e c t ( i i ) Surface drag e f f e c t ( i i i ) Surface anchoring e f f e c t - k9 - According t o the f o l l o w i n g arguments, the f i r s t two e f f e c t s can not account f o r the cause of increased c r i t i c a l r e s o l v e d shear s t r e s s . ( i ) D i s l o c a t i o n Egress E f f e c t A h a r r i e r r e s u l t i n g from the change of surface c o n d i t i o n would be expected t o have an e f f e c t on the motion of d i s l o c a t i o n s and we s h a l l c a l l t h i s e f f e c t the " d i s l o c a t i o n egress e f f e c t " . The image force tending t o p u l l an edge d i s l o c a t i o n out of the surface i s r e s i s t e d by the work done accompanying the formation of new surface area. This e f f e c t has been considered by F r a n k 2 4 when surfaces are c l e a n . He came to the c o n c l u s i o n t h a t , except f o r l e a d , most m e t a l l i c c r y s t a l surfaces should o f f e r no r e s i s t a n c e t o the egress of d i s l o c a t i o n s under t h e i r own image f o r c e . This idea was e s t a b l i s h e d by the f a c t t h a t the energy of a d i s l o c a t i o n l o c a t e d near the surface i s always greater than would be a s s o c i a t e d w i t h the newly exposed surface caused by egress of the d i s l o c a t i o n . I n the case of z i n c , the surface r e s i s t i n g f o r c e , if b i s I . 9 8 x 1 0 5 erg/cm ( if = surface energy and b= Burger's v e c t o r ) and the energy of a d i s l o c a t i o n a few atoms away from the surface i s 2 . 6 3 x 1 0 5erg/cm. In f a c t , the surface energy of a z i n c c r y s t a l was reduced by the mercury coa t i n g making i t e a s i e r f o r d i s l o c a t i o n s t o egress out of the surface. Therefore, mercury coatings should have reduced the c r i t i c a l r e s o l v e d shear s t r e s s i f we consider the d i s l o c a t i o n egress e f f e c t only. ( i i ) Surface Drag E f f e c t Any r e s i s t a n c e t o the formation of new surface or shear a t the surface would be expected t o have an e f f e c t t o the passage of the d i s l o c a t i o n s . This e f f e c t w i l l be termed the "surface drag effect'. Consider the p o s s i b l e e f f e c t - 50 of such a surface drag on the operation of a F i s h e r single-ended surface source as shown i n F i g . 2 9 . F i g . 29 . F i s h e r Single-Ended Source. At the c r i t i c a l s t r e s s OTQ t o operate a single-ended source of l e n g t h 1, the force a c t i n g at the drag p o i n t i s given by m b l Gb 2 c _ where G i s shear modulus and b i s Burger's v e c t o r . The surface drag f o r c e i s equal t o i f b where 7f i s the surface free energy of the c r y s t a l . The r a t i o , q, of the f o r c e a c t i n g at the drag p o i n t to the surface f r e e energy i s given by £ b 9 q. = V y ' — y Thus, when q i s l e s s than unity, the surface drag f o r c e exceeds the i n i t i a l f o r c e t o operate the surface source and d i s l o c a t i o n s w i l l be pinned unless the s t r e s s i s r a i s e d s u f f i c i e n t l y . For the case of z i n c q = 2.25 greater than u n i t y . When the surface i s c l e a n , mercury c o a t i n g reduces the surface energy f u r t h e r . - 51 - Therefore, we do not expect any surface drag e f f e c t from amalgamation of zinc monocrystals. ( i i i ) Surface Anchoring E f f e c t D i s l o c a t i o n s t h a t i n t e r s e c t the surface can be anchored as a consequence of s e l e c t i v e l a t t i c e d i f f u s i o n of surface a c t i v e atom along the d i s l o c a t i o n p i p e . There i s the a d d i t i o n a l p o s s i b i l i t y t h a t d i s l o c a t i o n s l o c a t e d near t o but not i n t e r s e c t i n g the surface may a l s o be pinned by s e l e c t i v e s o l u t e atmosphere or p r e c i p i t a t e formation. This e f f e c t w i l l be c a l l e d "surface anchoring e f f e c t " . Considering c r y s t a l s t r u c t u r e of z i n c and atomic s i z e of z i n c and mercury (Zn: I.38A and Hg = I.57S), which favours s u b s t i t u t i o n a l type of s o l u t i o n , p o s s i b l e i n t e r a c t i o n between d i s l o c a t i o n and d i f f u s e d mercury w i l l be Suzuki type r a t h e r than C o t t r e l l type. H. Suzuki has pointed out t h a t p a r t i a l d i s l o c a t i o n s w i t h a s t a c k i n g f a u l t i n between can i n t e r a c t w i t h impurity atoms w i t h a chemical form of i n t e r a c t i o n . The few atomic l a y e r s which c o n s t i t u t e the s t a c k i n g f a u l t show f . c . c . s t r u c t u r e ( i n f . c . c . s t a c k i n g f a u l t l a y e r s are C P . Hex.) i n s t e a d of hexagonal. Therefore the s o l i d s o l u b i l i t y of i m p u r i t i e s contained i n the m a t r i x can very w e l l d i f f e r " w i t h i n " the s t a c k i n g f a u l t and " o u t s i d e " . The d i f f e r e n c e i s a thermochemical nature and may c o n t r i b u t e t o an e f f e c t i v e energy of b i n d i n g of the i m p u r i t y atoms to the extended d i s l o c a t i o n . Once an extended d i s l o c a t i o n aquires i t s e q u i l i b r i u m amount of s o l u t e i t may be d i f f i c u l t t o move compared t o the free d i s l o c a t i o n . In view of foregoing argument, surface anchoring e f f e c t o r i g i n a t e d from s e l e c t i v e l a t t i c e d i f f u s i o n of mercury atom along the d i s l o c a t i o n pipe or Suzuki type l o c k i n g of d i s l o c a t i o n s surpasses the other two e f f e c t s showing an - 52 - e f f e c t on increased c r i t i c a l r e s o l v e d shear s t r e s s . Long exposure time a f t e r mercury c o a t i n g and short time h o l d i n g of coated c r y s t a l s at elevated temperatures confirm the anchoring e f f e c t of d i f f u s e d mercury atoms i n c r e a s i n g the c r i t i c a l r e s o l v e d shear s t r e s s . C. THE EFFECT OF MERCURY COATING ON THE WORK HARDENING OF ZINC SINGLE CRYSTAL The mercury c o a t i n g on the surface of z i n c s i n g l e c r y s t a l has brought remarkable changes i n the deformation c h a r a c t e r i s t i c s such t h a t c r y s t a l s were e m b r i t t l e d w i t h the f o l l o w i n g observed r e s u l t s . (1) Increased work hardening slope i n stage A. (2) Decreased t r a n s i t i o n s t r a i n , from stage A t o stage B. (5) Increased work hardening slope i n stage B. (4) Decreased f r a c t u r e s t r e s s and s t r a i n . In the deformation of z i n c s i n g l e c r y s t a l s , recovery processes are operative above ~30°0. M o t t 2 5 has proposed that s t a t i c recovery i s due t o the climb motion of edge d i s l o c a t i o n s and suggested t h a t dynamic recovery a l s o could be based on the same atomic process. Seeger and T r a u b l e 2 6 observed the fanning of s l i p l i n e s , shown s c h e m a t i c a l l y i n F i g . JO,which does not appear at lower temperature and came t o the co n c l u s i o n t h a t the t h e r m a l l y a c t i v a t e d recovery process i n z i n c i s due t o the climb motion of edge d i s l o c a t i o n s . This idea makes an a t t r a c t i v e c o n t r a s t i n r e l a t i o n s h i p t o the case of face centered cubic metals i n which cross s l i p by screw d i s l o c a t i o n s p l a y s an analogous r o l e f o r dynamic recovery. - 53 - L X .-tea F i g . 3 0 - Schematic P i c t u r e of Fanning Process at both ends of the same s l i p l i n e . Hi rath, et a l have shown t h a t h i g h l y mobile vacancies condense t o form a d i s l o c a t i o n r i n g . According t o t h e i r argument, the a n i s o t r o p i c nature of the hexagonal c r y s t a l s t r u c t u r e f o r c e s these d i s l o c a t i o n r i n g s to stay on the b a s a l plane and they are h i g h l y immobile because t h e i r Burger's vector i s p e r p e n d i c u l a r t o the b a s a l plane. Consequently, t h i s k i n d of vacancy or vacancy group condensation which occurs i n s t a t i c or dynamic recovery process enables us t o e x p l a i n the observed work hardening c h a r a c t e r i s t i c s of hexagonal metals. D i s l o c a t i o n r i n g s w i t h diameter l e s s than lOoS have no s u b s t a n t i a l e l a s t i c s t r e s s f i e l d because of t h e i r d i p o l e c h a r a c t e r i s t i c s 2 6 . However, these d i s l o c a t i o n r i n g s can act as short range obstacles r e s t r a i n i n g the motion of g l i d e d i s l o c a t i o n s . The number of vacancie i s p r o p o r t i o n a l t o the degree of deformation and as a consequence, the number of d i s l o c a t i o n r i n g s a l s o increases w i t h s t r a i n . The unbalance of counter compensating processes, namely, the formation of d i s l o c a t i o n r i n g s and t h e i r e l i m i n a t i o n through the climb motion provide the understanding of work hardenin i n hexagonal metals. Though the d i s l o c a t i o n r i n g s are e n e r g e t i c a l l y more stabl e than a t o m i c a l l y dispersed vacancies, they are not under thermodynamic equibrium. Therefore they can be annealed out by s t a t i c or dynamic recovery process. The t r a n s i t i o n from stage A t o B i s a t t r i b u t e d t o a c r i t i c a l concentration of d i s l o c a t i o n r i n g s r e s u l t i n g from the unbalance of the above mentioned counter compensating processes. The changes of work hardening c h a r a c t e r i s t i c s of coated c r y s t a l s can be explained by the i n t e r a c t i o n between d i s l o c a t i o n r i n g s and d i f f u s e d mercury atom. Microscopic examination t o detect the d i s t ance of d i f f u s i o n was not s u c c e s s f u l due t o the l a c k of a d i s t i n c t boundary r e s u l t i n g from the formation of any new phase or compound. D i f f u s i o n a l s o occurs during the deformation and increased number of s t r u c t u r a l defects a c c e l e r a t e the d i f f u s i o n process. The increased p e n e t r a t i o n of mercury atoms r e s u l t i n g from long exposure time or higher temperature treatment should cause more embrittlement, due to enhanced d i f f u s i o n of mercury atoms and hence an increased i n t e r a c t i o n w i t h the d i s l o c a t i o n r i n g s . Therefore a r e d u c t i o n of dynamic recovery r e s u l t s from the formation of s t a b l e short range o b s t a c l e s , causing s u b s t a n t i a l changes i n the work hardening c h a r a c t e r i s t i c s . From the arguments developed w i t h the a i d of deformation theory of hexagonal metals, we reach the f o l l o w i n g summaries. (1) The i n t e r a c t i o n between d i f f u s e d mercury atoms and d i s l o c a t i o n r i n g s i s r e s p o n s i b l e f o r increased work hardening slope i n stage A and decreased t r a n s i t i o n s t r a i n from stage A t o B. (2) Increased amount of p r e s t r a i n introduces more d i s l o c a t i o n r i n g s which can i n t e r a c t w i t h d i f f u s e d mercury atoms r e s u l t i n g i n e a r l y f a i l u r e of c r y s t a l s . (3) High temperature t e s t s support the r o l e of d i f f u s i o n i n l i q u i d metal embrittlement. High temperatures a c c e l e r a t e both surface and l a t t i c e d i f f u s i o n promoting the p o s s i b i l i t i e s of i n t e r a c t i o n between d i f f u s e d - 55 mercury atoms and d i s l o c a t i o n r i n g s . (k) The increase of work hardening slope i n stage B and decreased f r a c t u r e s t r e s s and s t r a i n can be exp l a i n e d by analogous argument as alr e a d y mentioned. D. PROPOSED MECHANISM FOR CRACK INITIATION severe twinning preceded the f r a c t u r e . C a r e f u l metallographic examination revealed that crack was propagated along the b a s a l plane i n twinned p a r t . The r e l a t i o n s h i p between the shear and the u n d i s t o r t e d plane which describes the twinning i n z i n c can be i l l u s t r a t e d by F i g . 31. In non-coated c r y s t a l s t e s t e d i n t e n s i o n at room temperature, (OOOl) In twin >i K 2 After "*f twinning Twinning Plane (I0T_) (0001) In matrix K (1012) In matrix F i g . 31* Geometry of Twin i n Z i n c . The common form of twin i n z i n c i s a compound t w i n i n Vwhich we have K x = (1012) K 2 = (1012) ^_ = [1011] -Jjfe = [1011] - 56 - where K_ = the twinning plane or the f i r s t u n d i s t o r t e d plane, K 2 = the second u n d i s t o r t e d plane 7£ 1 = shear d i r e c t i o n and = the d i r e c t i o n defined by the i n t e r s e c t i o n of the plane of shear w i t h K 2. The plane of shear i s the plane which i s mutually p e r p e n d i c u l a r t o Kx and K 2, and contains and ^  2 . A f t e r twinning, the angle between (0001) matrix and (0001) t w i n 2 S i s 94° and we can apply Zeners model f o r crack i n i t i a t i o n . I t i s conceivable that twin boundary performs the f u n c t i o n of st a b l e obstacle against the motion of d i s l o c a t i o n s and d i s l o c a t i o n s on a s l i p plane emanated from a Frank-Read source encounter a b a r r i e r (twin boundary) where they w i l l p i l e up e x e r t i n g considerable pressure on the few of them at the head of l i n e . As the pressure b u i l d s up, there are two a l t e r n a t i v e s , (1) the obstacle w i l l be overcome and s l i p w i l l continue, (2) the l e a d i n g d i s l o c a t i o n s w i l l be f o r c e d together t o form a crack nucleus. This idea i s i l l u s t r a t e d diagram<atically i n F i g . 32. F i g . 32. Zener's Model f o r the N u c l e a t i o n of Crack by D i s l o c a t i o n Coalescence as an A l t e r n a t i v e t o S l i p Propagation. - 57 Therefore, i f d i s l o c a t i o n s moving on the (0001) matrix p i l e up against t w i n boundary, a wedge-shaped v o i d normal t o the (0001) matrix and almost p a r a l l e l to (0001) twin can be formed. This i m p l i e s that crack can be nucleated from t h i s v o i d and propagated along (0001) twin (see F i g . 2k). When the exposure time a f t e r mercury c o a t i n g was short (5-15 mins) the c r y s t a l s f a i l e d by Zener type crack i n i t i a t i o n . Of course, f r a c t u r e occurred a t l e s s shear s t r a i n compared t o uncoated c r y s t a l s because of the shortening of stage A. When the time of exposure i n a i r a f t e r mercury c o a t i n g increased beyond 15 mins., a completely d i f f e r e n t type of f r a c t u r e appeared. The f r a c t u r e plane was the b a s a l plane of matrix c r y s t a l and specimens f a i l e d i n stage A before twins occur. This k i n d of f r a c t u r e was a l s o observed i n p r e s t r a i n e f f e c t and higher temperature e f f e c t experiments. The number of d i s l o c a t i o n r i n g s formed by the condensation of vacancies and then s t a b i l i z e d by d i f f u s e d mercury atoms could be increased under above mentioned experimental c o n d i t i o n s . Therefore, i t i s understandable that these r i n g s act as s h o r t - range obstacles against the motion of d i s l o c a t i o n s . 2 9 Gilman and Read have i n v e s t i g a t e d the formation of t e n s i l e k i n k w i t h v a rious shapes of zi n c monocrystals. They came t o the co n c l u s i o n t h a t both a x i a l t w i s t i n g and curvature of the surface r e s u l t i n g from t e n s i l e k i n k can occur i f the shear s t r a i n s due t o s l i p p i n g on a given b a s a l plane are heterogeneous across the b a s a l plane. They a l s o observed t h a t p l a t e d f i l m s of copper a f f e c t e d the appearance of the su r r a t e d surfaces by i n c r e a s i n g t h e i r i n t e n s i t y . This suggests t h a t the egress of d i s l o c a t i o n was d i s t u r b e d by p l a t e d copper f i l m s thereby i n t r o d u c i n g t e n s i l e k i n k s . During the t e n s i l e deformation of both coated and uncoated c r y s t a l s , s e r r a t e d surfaces w i t h a - 58 s e r i e s of small t e n s i l e k i n k s were observed and more embryos of t e n s i l e k i n k appeared i n coated and longer exposed specimens (see metallographic obser v a t i o n s ) . I n t e r a c t i o n between d i f f u s e d mercury atoms and d i s l o c a t i o n s or d i s l o c a t i o n r i n g s induced heterogeniety i n s l i p process r e v e a l i n g t e n s i l e kinks on the surface of c r y s t a l s . Frequent f a i l u r e of mercury coated c r y s t a l s at the k i n k bands suggest t h a t k i n k boundary can a l s o be a s t a b l e obstacle against d i s l o c a t i o n motion (see F i g . 25). Both increased number of s t a b i l i z e d d i s l o c a t i o n s r i n g s and k i n k boundaries perform the f u n c t i o n of s t a b l e obstacle f o r the p i l e up of d i s l o c a t i o n . In t h i s case, we can apply Bullough - Gilman - Rozhanskii model f o r crack i n i t i a t i o n shown i n F i g . 33- er O B S T A C L E ( 0001) F i g . 33- Schematic of Bullough - Gilman - Rozhanskii Model f o r Crack I n i t i a t i o n i n Z i n c . Under the a c t i o n of a t e n s i l e s t r e s s _> , the l a t t i c e i n the v i c i n i t y of a blocked group of d i s l o c a t i o n s bend about an a x i s p a r a l l e l t o the b a s a l plane and perpendicular t o Burger's v e c t o r . I f 6" i s s u f f i c i e n t l y large, a cleavage crack may be i n i t i a t e d along the b a s a l plane (see F i g . 26-27). - l>9 - V I . CONCLUSION (1) I n t e r a c t i o n between d i f f u s e d surface a c t i v e l i q u i d metal and o b s t a c l e s t o s l i p i s a p r e r e q u i s i t e f o r embrittlement during t e n s i l e deformation of z i n c s i n g l e c r y s t a l s o r i e n t e d f o r s i n g l e s l i p . (2) The p o s s i b l e o r i g i n s of s t a b l e o b s t a c l e s are considered t o be: (a) d i s l o c a t i o n r i n g s formed by vacancy condensation and s t a b i l i z e d by d i f f u s e d mercury atoms. (b) twin boundaries or t e n s i l e k i n k w a l l s r e s u l t i n g from non-uniform deformation across s l i p planes due t o the r e s t r a i n i n g of the motion of g l i d e d i s l o c a t i o n s by short-range obstacles ( s t a b i l i z e d d i s l o c a t i o n r i n g s ) . (3) The m o d i f i c a t i o n s of work hardening c h a r a c t e r i s t i c s of z i n c s i n g l e c r y s t a l s r e s u l t i n g from mercury c o a t i n g are summarized t o be: (a) increase i n c r i t i c a l r e s o l v e d shear s t r e s s , and increase of work hardening slope i n stage A and stage B. (b) decrease i n t r a n s i t i o n s t r a i n from stage A to B. (c) decrease i n f r a c t u r e s t r e s s and f r a c t u r e s t r a i n . (k) Cracks are i n i t i a t e d a t t e n s i l e kink w a l l s or twin boundaries, (depend on experimental c o n d i t i o n s ) . Relevant mechanisms f o r i n i t i a t i o n and propagation of cracks are considered t o be: (a) Zener-'s model f o r cracks i n i t i a t e d at twin boundaries. (b) Bullough - Gilman - Rozhanskii model f o r cracks i n i t i a t e d at k i n k w a l l s . APPENDIX A THERMODYNAMICS OF THE SPREADING OF LIQUIDS ON SOLID PHASE 3 0 The f r e e energy of a substance, at constant temperature, pressure and c o n c e n t r a t i o n i s defined as 1 ' P.T.N fre e surface energy per square centimeter where F = the f r e e energy of the substance and A = i t s surface area. ~if i s u s u a l l y expressed i n erg per square centimeter or dynes per centimeter. F i r s of a l l , the c o n d i t i o n f o r spreading t o occur i s t h a t f o r the e n t i r e system dF < 0 2 I t i s assumed t h a t i n the course of spreading of spreading of l i q u i d b on a surface a, the f o l l o w i n g area r e l a t i o n s are obtained. d A b = d A a b = " ^ a . .... 3 then \v ' p._ Let - ( b e designed as the f i n a l spreading c o e f f i c i e n t S°/ ' , V Q A J a then s b / a ' = ra< - (*v+ ..... 5 where P,T = constant and the surfaces s a t u r a t e d by the mutual components i s designated by the primes. For the s p e c i f i c case a t hand, component b i s the l i q u i d and a the s o l i d . We, t h e r e f o r e , redefine the spreading c o e f f i c i e n t s S L/ S = * s - ( * L + * L S ' ) ^ i t i a l 6 s L / S = 2TS - ( * L S ) s e m i - i n i t i a l ..... 7 s L4' = *Y " ( 2TL + 3L'S) F I N A L ••••• 8 As a primary guide from the above d i s c u s s i o n , we derive t h a t a necessary c o n d i t i o n f o r spreading i s - 62 - APPENDIX B DISLOCATION PIPE DIFFUSION 2 5 The term pipe d i f f u s i o n , which has f r e q u e n t l y been a p p l i e d t o d i f f u s i o n along d i s l o c a t i o n , might w e l l have been coined t o represent the l i n e of vacant s i t e s l y i n g under d i s l o c a t i o n l i n e . The core of the d i s l o c a t i o n may be defined as the l a s t l i n e of f i l l e d s i t e s i n the i n s e r t e d plane of an edge d i s l o c a t i o n together w i t h the l i n e of vacant s i t e s i n t o which t h a t plane would grow by negative climb. This i s i l l u s t r a t e d f o r a simple cubic l a t t i c e i n F i g . 1. An i n t e r s t i t i a l i n the d i s l o c a t i o n core may be defined as an atom i n the row of vacant, s i t e s i n the core; a vacancy, as an empty s i t e i n the l i n e of atoms i n the core ( F i g . 2 ) . INSERTED P L A N E \ /DISLOCATION LINE DISLOCATION LINE F i g . 1. Pare Edge D i s l o c a t i o n i n Simple Cubic L a t t i c e . F i g . 2. I l l u s t r a t i n g " I n t e r s t i t i a l and "Vacancy" i n Pure Edge D i s l o c a t i o n . - 63 - Consider a plane constructed p e r p e n d i c u l a r t o the d i s l o c a t i o n l i n e and not coincident w i t h a r e s t p o s i t i o n of an i n t e r s t i t i a l atom i n the d i s l o c a t i o n . The p r o b a b i l i t y of an atom jumping from l e f t t o r i g h t across t h i s plane can be w r i t t e n . J.i - 2 = a c j ^ 1 Where J _ - 2 i s the f l u x from l e f t t o r i g h t across the plane,p^, i s the jump frequency of an atom i n an i n t e r s t i t i a l p o s i t i o n , and ac_ i s the p r o b a b i l i t y t h a t the i n t e r s t i t i a l s i t e t o the l e f t of the reference plane i s occupied by a t r a c e r atom (a = l a t t i c e parameter). The p r o b a b i l i t y of a jump i n the reverse d i r e c t i o n across the plane is then given by J 2 - 1 = a T T ( c i + a " | | ) ..... 2 Where the distance between r e s t p o s i t i o n o f i n t e r s t i t i a l atom i s assumed t o be a, and i s the l o c a l g radient i n i n t e r s t i t i a l t r a c e r atoms. I f the f r e e energy required t o create an i n t e r s t i t i a l atom i n the d i s l o c a t i o n core i s /\ G-j, then the p r o b a b i l i t y of a given s i t e i n the core c o n t a i n i n g an i n t e r s t i t i a l atoms i s p = exp (- AGi/RT) ..... 3 The p r o b a b i l i t y t h a t any occupied s i t e contains a t r a c e r atom i s simply the l o c a l c oncentration of t r a c e r atom C 0. The combined p r o b a b i l i t y of an i n t e r s t i t i a l s i t e c o n t a i n i n g an atom which i s a l s o a t r a c e r atom i s , then, the product C_ = C c exp (- /RT) ..... k - 64 - The net t r a c e r f l u x can be obtained, from equations ( 1 ) , (2) and (4) and i s given by J n e t = " & 2 PT e x p < " ^ G i / R T ) 5 Comparison of equation 5 w i t h F i c k s f i r s t law i n d i c a t e s tha D = a 2 f exp(- A G i / R T ) 6 Further J~ -^ i s simply the product of the v i b r a t i o n frequency of an i n t e r s t i t i a l atom on the d i s l o c a t i o n core, ^ and the p r o b a b i l i t y t h a t the atom w i l l acquire s u f f i c i e n t energy to cross the b a r r i e r between neighbouring s i t e s . I f the b a r r i e r between neighbouring s i t e s has height A G m , the jump frequency becomes H r= J>exp(- ^ G > T ) ..... 7 and equation 6 may be w r i t t e n D = a 2 y exp[ -( A G i + AGm)/RT] ..... 8 I t i s assumed t h a t , as soon as an i n t e r s t i t i a l atom i s created and separated from i t s "parent" vacancy by a s i n g l e atomic d i s t a n c e , i t no longer i n t e r a c t s w i t h t h a t vacancy. APPENDIX C RESULTS OF TENSILE TEST T e n s i l e Test R e s u l t s (specimens w i t h p r o t e c t e d end) Specimen No. r c ( K g / c m 2 ) 6 A ( K g / c m 2 / u . s . ) r A _ B ( K g / c m 2 ) *A-B(*> e_.(Kg/cm2/u.s.) T F (Kg/cm 2) Experimental C o n d i t i o n ZXS-X-1 44° 46° 1.71 10.3 19 150 62.5 101.0 413 Non-coated R.T. t e s t . ZX3 -C -3 46° 48° 1.69 11.2 20 l 4 o 6 3 . 0 102.7 394 Non-coated R.T. t e s t ZXS-D-3 48c k9° l . 8 l 10.0 - - - 16.2 81 ^30$ p r e s t r a i n e d , coated and 5 min. exposure. R.T. test ZXS-D-2 48° 49° I . 6 9 10.3 - — - 16.3 91 30$ p r e s t r a i n e d , coated and 5 min. exposure. R.T.test ZXI-P -2 46° 48 1.67 11.0 - - - 19.2 151 100$ p r e s t r a i n e d , coated and 5 min. exposure. R.T.test ZX3-L-2 47 ° 47° 1.78 13.0 - — — 26.2 153 105$ p r e s t r a i n e d , coated and 5 min. exposure. R.T.test ZXZ-F-4 46* 48° 1.63 10.3 18 125 - 40 .8 184 162$ p r e s t r a i n e d , coated and 5 min. exposure. P.T.test ZXI-F -3 46c 48° 1.65 10.0 18 i 4 o - 37.7 191 165$ p r e s t r a i n e d , coated and 5 min. exposure. R.T.test ZXI-N-3 44 d 46° 2.00 13.3 17 110 95 i o 4 . i 304 coated and 5 min. exposure. R.T.test '8 sees i n 50ccHg Appendix I I I (cont'd) T e n s i l e Test R e s u l t s (specimens w i t h protected end) Specimen No. X 0 Tc(Kg/cm2) 9 A(Kg/cm 2/u.s.) ^ ( K g / c m 2 ) rA_Bm 0 B(Kg/cm 2/u.s.) ^(Kg/cm 2) r f(#) Experimental C o n d i t i o n ZXS-F-3 48° 49° 1.99 17.2 21 95 75 100.0 267 A coated and 5 min. exposure. R .T.test ZXS-F-2 48° 49° 1.95 17.2 22 100 70 97.6 254 coated and 5 min. exposure. R.T.test ZXI-N-2 44° 46° 2.03 12.0 16 100 95 97.0 267 coated and 10 min. exposure. R.T.test ZXI-0-4 42° 45° 2.03 16.0 21 90 70 59.0 173 coated and 15 min. exposure. R .T .test ZXI-0-2 42° 2.06 17.1 22 80 65 61.6 179 coated and 15 min. exposure. R . T .test ZXI-M-3 42° 44° 2.07 12.6 - - - 13.2 62 coated and 30 min. exposure. R .T .test ZXI-M-2 42° 44° 2.12 14.3 - - - 14.5 72 coated and 30 min. exposure. R . T .test ZXI-L-k 44° 46° 2.12 13.6 - - - 8.7 73 coated and 60 min. exposure. R . T .test ZXI-0-3 42° 1+5° 2.11 9.7 - - - 6.1 38 coated and 60 min. exposure. R . T .test. ZXI-V-2 46° 4 7° 2.09 12.0 13.4 86 coated, 5 min. exposure, 5 min i n 50°C bath and quench t o R.T. R.T. t e s t 8 sees i n 50ccHg , OA ON i Appendix I I I (cont'd) T e n s i l e Test R e s u l t s (specimens w i t h p r o t e c t e d end) Specimen No. Xc 9vo T C ( Kg/cm2) ©A(Kg/cm2/l.s.) ^ A _ B ( K g / c m 2 ) rA.B(^) © B (Kg/cm 2/i.s.) ^ ( K g / c m 2 ) rf(*) Experimental C o n d i t i o n ZXI-V-3 46° 2.20 11.0 — — 13.2 90 coated, 5 min. exposure, 5 min. i n 50°C bath and quench t o R.T. R.T. t e s t ZXI-W-3 47° 48° 2.30 15.7 7-5 30 coated, 5 min. exposure, 5 min. i n 75° bath and quench t o R.T. R.T. t e s t ZXI-V-1 46° 47° 2.24 13 .8 — 9-3 44 coated, 5 min. exposure, 5 min. i n 75°C bath and quench t o R.T. R.T. t e s t ZXI-Y-3 48° 49° 2.52 — — 4 .6 7 coated, 5 min. exposure, 5 min. i n 95° bath and quench to R.T. R.T. t e s t ZXI-Y-2 48° k9° 2.46 ft- ' 5-5 10 coated, 5 min. exposure, 5 min. i n 95° bath and quench t o R.T. R.T. t e s t 8 sees i n 50ccHg 1 ON. - J Appendix I I I (cont'd) Results of T e n s i l e Test (specimens w i t h non-protected ends) Specimen No. X 0 K r c (Kg/cm 2) © A(Kg/cm 2/u.s.) T A_ B(Kg/cm 2) *A-B(*) 6 B(Kg/cm 2/u.s.) Experimental C o n d i t i o n ZXS-K-2 49° 1+9° 1.76 10.5 19 135 85 non-coated. R.T. t e s t ZX3-I-2 k6° 48° 1.71 10.5 - - - M A 100$ p r e s t r a i n e d , coated and 5 min. exposure. R.T. t e s t ZXS-T-3 46° 48° 1.73 15.3 - 135 - 150$ p r e s t r a i n e d , coated and 5 min. exposure. R.T. t e s t ZXS-T-2 k6° 48° 1.72 12 .0 - 115 65 200$ p r e s t r a i n e d , coated and 5 min. exposure. R.T. t e s t ZXS-W-3 kh° k6° 1.76 10.0 16 125 86 2 sees i n 50ccHg and 5 min. exposure. R.T. t e s t ZXS-H-2 1+7° k9 1-75 12.2 23 125 70 2 sees i n 50ccHg and 5 min. exposure. R.T. t e s t ZNX-F-2 kT kQ° 1.82 12.0 20 115 50 2 sees i n 50ccHg and 5 min. exposure. R.T. t e s t ZXS-J-1 kk° 1+6° 1.77 10.0 16 115 75 k sees i n 50ccHg and 5 min. exposure. R.T. t e s t ZX3-G-3 kQ° 50° 1.79 13.0 20 125 80 k sees i n 5 0 c cHg and 5 min. exposure. R.T. t e s t ZXII-E - 1 47° 48° 1.81 8.5 13 125 60 k sees i n 50ccHg and 5 min. exposure. R.T. t e s t ZX3-W-2 kk" k6° I . 8 3 11. k 16 110 - 6 sees i n 50ccHg and 5 min. exposure. R.T. t e s t A k sees i n 50ccHg O N C O Appendix I I I (cont'd) R e s u l t s of T e n s i l e Test (specimens w i t h non-protected ends) Specimen No. Xo %o T c (Kg/cm2; 9 A(Kg/cm 2/u.s.) 0T A_ B(Kg/cm 2) *A-B<*> 9 B(Kg/cm 2/u.s.) Experimental C o n d i t i o n ZXS-G-1 48° 50° 1.84 11.8 19. 115 - 6 sees i n 50ccHg and 5 exposure. R.T. t e s t min. ZXII-E-2 1+7° 48° 1.82 11.0 17 125 85 6 sees i n 50ccHg and 5 exposure. R.T. t e s t min. ZXS-U-1 ky 45° 1.96 12.3 15 100 - 8 sees i n 50ccHg and 5 exposure. R.T. t e s t min. ZXS-D-1 48° 49° 2.02 12.0 - - - 8 sees i n 50ccHg and 5 exposure. R.T. te s t min. ZXII-B-2 46° 46° 2.03 8 sees i n 50ccHg and 5 exposure. R.T. t e s t min. I VO - 70 - APPENDIX D ESTIMATION OF ERRORS C r i t i c a l r e s o l v e d shear s t r e s s i s obtained from the r e l a t i o n r t c = — sin X 0 cosXo where P i s l o a d , A i s i n i t i a l cross s e c t i o n a l area and X o a n ( 3. ^ o have the same meaning as defined p r e v i o u s l y . By t a k i n g n a t u r a l logarithms and d i f f e r e n t i a t i n g equation (1), the t o t a l e r r o r i n v o l v e d i n c a l c u l a t i n g c r i t i c a l resolved shear s t r e s s i s S% ^P + JA + (T(sinX 0) + Jfcos9\0) % ' P A s i n X 0 cos9vo The p o s s i b l e u n c e r t a i n t i e s a r e : (1) the load value from the c h a r t , the d e v i a t i o n p o i n t from l i n e a r i t y would be determined t o w i t h i n at l e a s t 0.2 d i v i s i o n i n k, hence h. = 2 ^ = 0 > 0 5 p V (2) specimen cross s e c t i o n , the micrometer could be read t o 0.001cm i n 0.05 cm, hence J A = 2(0.001) = Q k A 0.05 (3) the c r y s t a l o r i e n t a t i o n could be determined w i t h i n ±1° us i n g the Wulff net, hence f o r X D = 46° <f(sinXc) = 0.012 = Q Q ± 7 s i n X 0 0.719 - 71 - and f o r *\ 0 = 46 COS 0.012 0.695 = 0.017 Therefore, t o t a l u n c e r t a i n t i e s i n v o l v e d i n c r i t i c a l r e s o l v e d shear s t r e s s i s 7=r- = 0.074 or 7.4$ The flow s t r e s s values i n v o l v e a d d i t i o n a l parameter, the gage l e n g t h , v a r i a t i o n i n cross s e c t i o n a l area along gage s e c t i o n and the amount of mercury coated. E s p e c i a l l y , the amount of mercury coated on the surface of c r y s t a l s depends on the surface c o n d i t i o n (degree o f micro r e l i e f and p o s s i b l e contaminations) and t h i s w i l l a f f e c t the parameters defined f o r comparison but there i s no relevant way t o estimate the r e s u l t i n g e r r o r . - 72 - REFERENCES 1. N i c h o l s , H., and Rostoker, W., Acta Met. 9, 504 (1961). 2. Goryunov, U.V., Pertsov, N.V., and Rehbinder, P.A., So v i e t Physics "Doklady", 4, 840 (i960). 3. Heyn, E., J . I n s t . Metals 12, 3 (1914). 4. Rawdon, H.S., Proc ASTM 18, 2, 189 (I918). 5. Moor, R., and B e c k i n s a l e , S., J . I n s t . Metals, 23, 225 (1920). 6. M i l l e r , H.J., J . I n s t . Metals, 37, 183 (1927). 7. Rosenberg, R., and Cadoff, I . , Fracture of S o l i d s , E d i t e d by D.C. Drucker and J . J . Gilman (I962). 8. Likhtman, V . I . , and Shchukm, E.D., So v i e t Physics "Uspekhi", I.91 (I958). 9. Shchikin, E.D., Perstov, N.V., and Goryunov, U.V., S o v i e t Physics ( C r y s t a l l o g r a p h y ) , 4, 800 (1959). 10. Labzin, V.A. and Likhtman, V . I . , "Doklady", Akad Nauk, SSSR 121, 778 (I958). 11. Rehbinder, P.A., Likhtman, V.I., and Kochanova, L.A., "Doklady", Akad Nauk, SSSR 111, 1276 (1956). 12. Likhtman, V.I., Kochanova, L.A., and Bryukhanova, L.S., "Doklady" Akad Nauk, SSSR 120, 757 (1958). 13. Kamdar, M.H., and Westwood, A.R.C., Embrittlement of Z i n c Monocrystals and B i c r y s t a l s by Mercury and G a l l i u m , RIAS, March (I965). 14. Kamdar, M.H ., and Westwood, A.R.C., Concerning L i q u i d Metal Embrittlement P a r t i c u l a r l y of Zinc Monocrystals by Mercury, RIAS, Dec. (I962). 15. Perstov, N.V., and Rehbinder, P.A., "Doklady", Akad Nauk, SSSR, 124, 307, (1959). 16. Anderson, E.A., Metals Handbook, (1948). 17. Simson, C.Von., Z. Physik Chem. 109, 192 (1924). 18. Boas, W., An In t r o d u c t i o n t o the Physics of Metals and A l l o y s , 67, (1947). 19. J i l l s o n , D.C, Trans. AIME, 188 (1950). - 73 - References (cont'd) 20. Harkins, W.D., P h y s i c a l Chemistry of Surface, Reinhold Pub. Co., N.Y. (1952). 21. F r i c k e , R., Z. Elektrochem. , 52, 72 (1948). 22. Pleteneva, N.A., and Fedoseeva, N.P., "Doklady", Akad Nauk, SSSR 151, 2 (1963). 23. Love, G.R., Acta Met. 12, 6 (1964). 24. Frank, F.C., Mathematical Theory of S t a t i o n a r y D i s l o c a t i o n , PhiL Mag. Suppl., July(1952). 25. Mott, N.F., P h i l . Mag. 43 (1952), P h i l . Mag. 44 (1953). 26. Seeger, A. Von., and T r a b l e , H., Z. Metalkunde (i960). 27. H i r s c h , P.B., S i l c o x , J . , Smallman, R.E., and Westmacott, K.H., P h i l . Mag. 3 897/(1958). 28. Zener, C , " F r a c t u r i n g of Metals", pp.3-31 ASM (1948). 29. Gilman, J . J . , Read, T.A., Trans. AIME 194, 875 (1952). 30. Bondi, A., Chem. Rev., 52, 427 (1953). 

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