Precipitation at coherency loss in Cu-0.35 wt pct Cr
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ing tl~at the m i c r o s t r u c t u r e c o n s i s t s of a m i x t u r e of c o h e r e n t p a r t i c l e s (about which t h e r e is t y p i c a l s t r a i n f i e l d c o n t r a s t ) and r o d s h a p e d p a r t i c l e s which a p p e a r to b e n o n c o h e r e n t . F i g . 2 i s a b r i g h t f i e l d p h o t o g r a p h of a foil aged 2 h at 600~ so a s to i n c r e a s e the n u m b e r of p a r t i c l e s r e l a tive to the s p e c i m e n a g e d 3 h and t i l t e d so a s to r e d u c e m a t r i x c o n t r a s t and whose o r i e n t a t i o n is a p p r o x i m a t e l y (111). A n a l y s i s b y s t e r e o g r a p h i c p r o j e c t i o n shows that the i m a g e s of the s m a l l r o d s l i e p a r a l l e l to (110) d i r e c t i o n s a s w e l l as in d i r e c t i o n s at r i g h t a n g l e s to t h e s e . F i g . 3 is a s e l e c t e d a r e a d i f f r a c t i o n p h o t o g r a p h of a f e l l of the above m a t e r i a l t i l t e d to S = 0 on the (110) zone and f o r which g = 004. E x t r a r e f l e c t i o n s o t h e r than those from the matrix are seen about the {111} and 9
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EXPERIMENTAL A Cu-0.35 wt pct Cr a l l o y was p r e p a r e d f r o m high p u r i t y m a t e r i a l b y m e l t i n g in an a l u m i n a c r u c i b l e and double c a s t i n g into a cold c o p p e r m o l d under a r g o n in a v a c u u m t y p e f u r n a c e . The r e s u l t a n t b a r s w e r e cold s w a g e d to 6 m m d i a m r o d and then h o m o g e n i z e d at 1000~ f o r 168 h in a r g o n . F o i l f o r e l e c t r o n m i c r o s c o p i c e x a m i n a t i o n was p r e p a r e d b y cold r o l l i n g the h o m o g e n i z e d r o d to 0.25 m m s t r i p . P r i o r to aging, the foil was solution t r e a t e d in a r g o n at 1000~ f o r 1 h and w a t e r quenched. RESULTS F o i l a g e d 3 h at 600~ was e x a m i n e d in the e l e c t r o n m i c r o s c o p e . F i g . 1 is a b r i g h t f i e l d m i c r o g r a p h s h o w Y. KOMEM is Lecturer, Department of Materials Engineering, Israel Institute of Technology, The Technion, Haifa, Israel. J. REZEK is Professor of Engineering Materials, University of Windsor, Windsor,
Ontario, Canada. Manuscript submitted August 16, 1974. METALLURGICAL TRANSACTIONS A
Fig. 1--Cu-0.35 wt pct Cr aged at 600~ for 3 h. The structure consists of a mixture of coherent particles about which there is strain field contrast and non-coherent rod shaped particles.
VOLUME 6A, MARCH t 9 7 5 - 5 4 9
Fig. 2--Cu-0.35 wt pct Cr aged at 600~ for 2 h. The foil orientation is almost (iii~ The foil has been tilted to reduce matrix c o n t r a s t a n d s h o w s r o d s h a p e d p a r t i c l e s in and
Fig. 4--Same area as ]:ig. 3 tltted to reduce matrix contrast. Particles markedx, yand z are in (111), (i12) and (113) directions respectively.
d i r e c t i o n s .
DISCUSSION Previous work on the Cu-0.15 pct Cr system by Knights and Wilkes a has shown that this alloy, when aged 4 h at 600~ produces a microstructure simila
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