Directionality in a precipitation-hardened alloy
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the alloy c o r r e s p o n d e d to the B r i t i s h s p e c i f i c a t i o n LM 11 for c a s t i n g alloys, the i m p u r i t y l e v e l s b e i n g g e n e r a l l y lower than those in the u s u a l s t r i p s p e c i f i c a t i o n HS 15. The alloy was c a s t with a s l a b t h i c k n e s s of 63 m m , homogenized, hot r o l l e d and cold r o l l e d to a f i n a l t h i c k n e s s of 1.2 m m . The s t r i p was s o l u t i o n t r e a t e d at 525~ and cups were d r a w n in the heat t r e a t e d conditions s u m m a r i z e d below: AgingTreatment
P. JOBSONANDW. T. ROBERTS The d i r e c t i o n a l p l a s t i c b e h a v i o r of s i n g l e c r y s t a l and p o l y c r y s t a U i n e s a m p l e s of s i n g l e phase cubic m e t a l s is well documented, and the b e h a v i o r is p r e dicted by d e f o r m a t i o n m o d e l s b a s e d on the Bishop and Hill analysis.~ M o r e r e c e n t l y , a n i s o t r o p y in a cubic m e t a l with a second p h a s e in the f o r m of p l a t e lets on a specific type of c r y s t a l l o g r a p h i c plane in the m a t r i x has b e e n studied, e'3 Single c r y s t a l s of A14 pct Cu were t e s t e d in plane s t r a i n c o m p r e s s i o n a f t e r v a r i o u s heat t r e a t m e n t s . C r y s t a l s aged to cont a i n 0' p r e c i p i t a t e showed a s m a l l e r v a r i a t i o n of s t r e n g t h with o r i e n t a t i o n than c r y s t a l s in e i t h e r the s o l u t i o n t r e a t e d or the o v e r a g e d conditions. The o v e r aged c r y s t a l s b e h a v e d in a m a n n e r s i m i l a r to that of p u r e a l u m i n u m , i.e., when the data f r o m c r y s t a l s of d i f f e r e n t o r i e n t a t i o n s w e r e c o n v e r t e d to s h e a r s t r e s s / s h e a r s t r a i n plots u s i n g the a p p r o p r i a t e M f a c t o r , all the c u r v e s were within a n a r r o w band c o r r e s p o n d i n g to a single @y c u r v e . C r y s t a l s aged to c o n t a i n 0 ' p r e c i p i tate, on the other hand, showed a wide d i v e r g e n c e f r o m this b e h a v i o r , whilst the s u p e r s a t u r a t e d condition behaved in a m a n n e r i n t e r m e d i a t e b e t w e e n the o v e r a g e d and the 0' conditions. The d e p a r t u r e of the s u p e r s a t u r a t e d m a t e r i a l f r o m s i n g l e phase b e h a v i o r was a t t r i b u t e d to the f o r m a t i o n of 0" p r e c i p i t a t e d u r i n g deformation. The m o d e l for d e f o r m a t i o n of c r y s t a l s c o n t a i n i n g 0' involves the m a i n t e n a n c e of c o m p a t i b i l i t y between the m a t r i x and p r e c i p i t a t e p l a t e l e t s by both d e f o r m a t i o n and r o t a t i o n of the p l a t e l e t s . Shear s t r a i n s on {100} planes perpendicular to the habit plane are accommodated by rotations of the platelets. The analysis predicts that hard orientations tend to be strengthened less by the precipitate than soft orientations, in agreement with the observations. In polycryst
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