A transmission electron microscopic investigation of phase transformations in MP35N
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A Transmission Electron Microscopic Investigation of Phase Transformations in MP35N M. RAGHAVAN,
B. J. BERKOWITZ,
AND
R. D. KANE
High strength cobaR-nickel base multiphase (MP) alloys are characterized by an excellent combination of strength and corrosion resistance. The multiphase alloys, originally developed by G. D. Smith, t have 20 pct Cr, I0 pct Mo, and the balance made up of cobar and nickel. The MP alloys strengthen rapidly during cold working and further strengthening is obtained b y a g i n g t r e a t m e n t . ~~ D u r i n g r e c e n t i n v e s t i g a t i o n s o n t h e h y d r o g e n e m b r i t t l e m e n t s u s c e p t i b i l i t y of MP35N, transmission electron microscopy snowed n o d i f f e r e n c e s in m i c r o s t r u e t u r e t h a t c o u l d d i r e c t l y a c c o u n t f o r d i f f e r e n c e s in h y d r o g e n e m b r i t t I e m e n t s u s c e p t i b i l i t y . 6,v A l s o , it w a s n o t e d t h a t p r e v i o u s i n v e s t i g a t o r s a t t r i b u t e d t h e s t r e n g t h e n i n g of t h e M P a l l o y s t o t h e f o r m a t i o n of a h e x a g o n a l c l o s e p a c k e d e-phase from the parent fee y-phase during deformation, Strengthening during subsequent aging was s u g g e s t e d d u e t o t h e s e g r e g a t i o n of M o t o t h e e - p h a s e b o u n d a r i e s e v e n t u a l l y l e a d i n g t o f o r m a t i o n of a CoaMo c o m p o u n d , ~ A f t e r a d e t a i l e d l i t e r a t u r e s u r v e y on t h e s t r e n g t h e n i n g m e c h a n i s m of t h e M P 3 5 N a l l o y , it w a s r e a l i z e d t h a t d e f o r m a t i o n t w i n s c o u l d f o r m in t h i s aIloy which have the s a m e m o r p h o l o g y a s the e - p h a s e . Hence a more detailed investigation was initiated to e s t a b l i s h t h e s t r e n g t h e n i n g m e c h a n i s m of t h e M P 3 5 N alloy d u r i n g cold w o r k i n g and s u b s e q u e n t aging. M. RAGHAVAN and B. J. BERKOWITZ are with Exxon Research and Engineering Company, Linden, NJ 07036. R. D. KANE is with Battelle Houston Operations, Houston, TX 77020. Manuscript submitted April 26, 1979. METALLURGICAL TRANSACTIONS A
Fig. 1-MP35N alloy cold worked 59 pct; bright-field images showing (a) single set and (b) intersecting sets of deformation twins. Arrows in (a) indicate stacking fault fringes.
Fig. 2 MP35N alloy cold rolled 59 pct, typical [ 0 i l ] ~ selected area diffraction pattern showing twin reflections (compare with Fig. 3b)
Streaks run normal to the thin direction of the twins, along [ 111 ] 7"
ISSN 0360-2133 / 80/0111-0203500.75 / 0 9 1980 AMERICAN SOCIETY FOR METALS AND THE METALLURGICAL SOCIETY OF AIME
VOLUME 11A, JANUARY 1980-203
T o p o s i t i v e l y identify the s e c o n d p h a s e that f o r m s d u r i n g d e f o r m a t i o n and to c o n f i r m the p r e v i o u s T E M r e s u l t s , 6'v a c a r e f u l e l e c t r o n d i f f r a c t i o n s t u d y was r e q u i r e d . S a m p l e s of MP35N a l l o y (35 pct Co, 35 pct Ni, 20 pct Cr, and
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