Mercury embrittlement of age-hardened cu-1.9wt Pct cobalt and Cu-3.6 wt Pct Titanium
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THE c a t a s t r o p h i c
effect of m e r c u r y on the s t r e n g t h of m e t a l s is well known. 1 R o s e n b e r g and Cadoff 2 have shown that g r a i n s i z e , c o m p o s i t i o n and a m o u n t of p r e s t r a i n have a s i g n i f i c a n t effect on the d e g r e e of e m b r i t t l e m e n t of copper solid s o l u t i o n s . They o b s e r v e d an i n c r e a s e in e m b r i t t l e m e n t with i n c r e a s i n g y i e l d s t r e n g t h obtained by s o l i d - s o l u t i o n alloying. Stoloff, e t a l . 3 have shown that m e r c u r y e m b r i t t l e m e n t of copp e r alloys i n c r e a s e s as the p r o p e n s i t y to c r o s s slip d e c r e a s e s . In light of the above effects of y i e l d - s t r e n g t h and mode of slip in s o l i d - s o l u t i o n a l l o y s , it was d e cided to i n v e s t i g a t e m e r c u r y e m b r i t t l e m e n t in a g e h a r d e n e d copper a l l o y s . In such a l l o y s , the type of slip and y i e l d - s t r e n g t h can be v a r i e d by heat t r e a t m e n t , while o v e r a l l alloy c o m p o s i t i o n r e m a i n s u n changed. C o p p e r - c o b a l t is an ideal candidate for t e s t i n g in a liquid m e t a l e n v i r o n m e n t . Its a g e - h a r d e n i n g c h a r a c t e r i s t i c s a r e well u n d e r s t o o d . 4-6 A c o b a l t - r i c h , fee, c o h e r e n t p r e c i p i t a t e f o r m s upon aging. Up to the peak s t r e n g t h , these p a r t i c l e s a r e s h e a r e d by moving d i s l o c a t i o n s , and a b y p a s s m e c h a n i s m is o p e r a t i v e beyond this point. C o h e r e n c y is not lost during n o r m a l t i m e t e m p e r a t u r e c o m b i n a t i o n s in aging. An additional a l loy, C u - T i , was c h o s e n b e c a u s e of its high s t r e n g t h and the l a r g e v a r i a t i o n s in m i c r o s t r u c t u r e s which can be obtained by a p p r o p r i a t e heat t r e a t m e n t . 7
EXPERIMENTAL
MATERIALS
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The Cu-1.9 wt pct Co alloy was supplied by Olin Corporation in the form of cold-rolled, 0.125 in. thick H. T. MICHELS, formerly Graduate Student, Department of Metallurgy and Materials Sciences,New York University, Bronx, N. Y., is now with The International Nickel Company, Inc., Paul D. Merica Research Laboratory, Sterling Forest, Suffern, N.Y.I.B. CADOFF and E. LEVINE are Professor and Associate Professor, respectively, Department of Metallurgyand Materials Sciences,New York University. This paper is based upon a thesis submitted by H. T. MICHELS in partial fulfillment of the requirements of the degree of Doctor of Philosophy at New York University. Manuscript submitted February 3, 1972. METALLURGICALTRANSACTIONS
s h e e t . The C u - 3 . 6 wt pet T i alloy p r e p a r a t i o n was d e s c r i b e d e a r l i e r .7 Heat t r e a t m e n t , t e n s i l e t e s t i n g and light and e l e c t r o n m i c r o s c o p y s a m p l e p r e p a r a t i o n w e r e c a r r i e d out on both alloys as p r e v i o u s l y d e s c r
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