Transformation of the Fcc structure to the hexagonal structure in alpha brass subjected to cold work
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r a t e in s p e c i m e n s p r e s t r a i n e d 10.2 pct ; the i n c r e a s e in the d e n s i t y of t h e s e p r e c i p i t a t e s with cold work offs e t s the i n c r e a s e of d i s l o c a t i o n d e n s i t y . The effect of i n - s i t u s t r a i n i n g on the e v o l u t i o n of c h r o m i u m p r e c i p i t a t i o n in the n i c k e l - r i c h l a m e l l a e is i l l u s t r a t e d in Fig. 2 which c o m p a r e s the s t r u c t u r e in the s h o u l d e r s e c t i o n to that in the gage s e c t i o n of a c r e e p s p e c i m e n t e s t e d at 760~ and e x p o s e d to t e m p e r a t u r e for 10 h r . It is quite c l e a r that the c o r m a l p r o c e s s of c e l l u l a r p r e c i p i t a t i o n in the n i c k e l - r i c h l a m e l lae was d i s r u p t e d , and was r e p l a c e d by d i s c r e t e p a r t i cles of a c h r o m i u m - r i c h p h a s e . E x a m i n a t i o n of s p e c i m e n s exposed to c r e e p d e f o r m a t i o n for t i m e s as long as 2000 h r and at v a r i o u s s t r e s s l e v e l s showed that the r e p l a c e m e n t of c e l l u l a r p r e c i p i t a t e s b y d i s c r e t e p a r t i c l e s of a c h r o m i u m - r i c h p h a s e was a g e n e r a l p h e n o m e n o n . F u r t h e r m o r e , it was e v i d e n t that the p r e c i p i t a t i o n of c h r o m i u m in the gage s e c t i o n was g o v e r n e d by a d i f f e r e n t m e c h a n i s m t h a n that which c o n t r o l s the c e l l u l a r p r e c i p i t a t i o n . W h e r e a s the c l a s s i c a l growth and c o n g l o m e r a t i o n of p a r t i c l e s o c c u r r e d in the gage s e c t i o n a f t e r a long e x p o s u r e to t e m p e r a t u r e v e r y little change was e v i d e n t in the c e l l u l a r s t r u c t u r e . This p r o g r a m was supported by the Advanced R e s e a r c h P r o j e c t s Agency u n d e r C o n t r a c t No. DAHC 1567-C-0176. 1. Ram Kossowsky: Met. Trans., 1970, vol. l, pp. 1623-27. 2. Ram Kossowsky: Semi-Annual Report, ARPA order 981, Contract DAHC 15-67-C-0176, December 1969, pp. 33-65; also, Met. Tran~, 1970, vol. 1, pp. 1909-19. 3. D. Turnbull and M. N. Treaftis: ActaMet., 1955, vol. 3, pp. 43-54. 4. R. Kossowsky, W. C. Johnston, and B. J. Shaw: Trans. TMS-AIME, 1968, voL 245, pp. 1219-25. 5. D. Turnbull: ActaMet., 1955, vol. 3, pp. 55-63. 6. B. L. Averbach: Trans. ASM, 1949, vol. 41, pp. 262-66. 7. G. R. Speich: Trans. TMS-AIME, 1968, vol. 242, pp. 1359-67.
(b) F i g . 2 - - ( a ) S h o u l d e r s e c t i o n of c r e e p s p e c i m e n , R - 6 9 - 4 , l a m e l l a r e u t e c t i c N i - 5 1 C r , T a b l e II, R e f . 2, t e s t e d at 15,000 p s i a n d 760~ T e s t i n t e r r u p t e d a f t e r t o t a l s t r a i n of 1.5 p c t d u r a t i o n of t e s t 10 h r . T w o - s t a g e c a r b o n r e p l i c a . (b) G a g e s e c t i o n of s a m e s p e c i m e n . M a g n i f i c a t i o n 2425 t i m e s .
be s u f f i c i e n t to a c c o u n t for the o b s e r v e d i n c r e a s e in the gr
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