Grain boundary embrittlement in a beta titanium alloy
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VOLUME6A, APRIL 1975-947
belief that the C and O concentration profiles are relat e d to s y s t e m c o n t a m i n a t i o n r a t h e r t h a n b e i n g a n i n h e r e n t c h a r a c t e r i s t i c of t h e s p e c i m e n u n d e r e x a m i n a l i o n . On t h i s b a s i s , o n l y t h e T i a n d C r e n r i c h m e n t a t t h e f r a c t u r e s u r f a c e c a n b e c o n s i d e r e d a s i n d i c a t i v e of the system presently under examination. A p r e v i o u s i n v e s t i g a t i o n b y t h e a u t h e r I2 h a s s h o w n that grain boundary segregation associated embrittlem e n t o c c u r r i n g d u r i n g s o l u t i o n t r e a t m e n t of m a r a g i n g steel may be virtually eliminated by either increasing the solution treatment temperature or increasing the
Fig. 1--Scanning Electron Micrograph of RMI 38644 solution treated at 927~ rain-air cooled. Initial impact velocity: 130 in. per s, I
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t r e a t e d at 927"C-30 r a i n - a i r cooled. 4
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Fig. 3 - - I n e r t - i o n s p u t t e r i n g s e g r e g a t i o n profile of v a r i o u s e l e ments on RMI 38644 g r a i n b o u n d a r i e s (solution t r e a t m e n t 927"C-30 r a i n - a i r cooled). 948-VOLUME 6A, APRIL 1975
Fig. 4--Scanning E l e c t r o n M i c r o g r a p h s of RMI 38644 solution t r e a t e d at (a) 927"C, (b) 1060~ and (c) I390"C for t h r and w a t e r quenched. Initial impact velocity: 130 in. p e r s. METALLURGICAL TRANSACTIONS A
currecl following general yield after solution treatment at 927~ and water quenching, i.e., PF > PGY, the dynamic fracture toughness in this e a s e has been d e t e r mined utilizing the "equivalent energy" c r i t e r i a ) 3 Subsequent fractography, Fig. 4, confirms the fact that increasing the cooling rate from the solution treatment temperature r e s u l t s in dimple, ductile fracture and completely s u p p r e s s e s the intergranular f r a c ture morphology previously observed in the air cooled condition. However, increasing the solution treatment temperature leads to increasing amounts of quasicleavage and cleavage fracture. In s u m m a r y , m a x i m u m dynamic fracture toughness in solution treated RMI 38644 is observed with lower solution treatment temperatures and faster cooling r a t e s . The lower treatme
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