Cu-Zr and Cu-Zr-Cr alloys produced from rapidly quenched powders
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450~ and w e r e s u b s e q u e n t l y c o m p a c t e d in c o p p e r c a n s (in a d r y box with 0.0003 vol pct w a t e r v a p o r ) . The c a n s w e r e e v a c u a t e d and hot e x t r u d e d , s e e T a b l e I. M e t a l l o g r a p h i c i n s p e c t i o n and s p e c i f i c g r a v i t y m e a s u r e m e n t s i n d i c a t e d that a l l a l l o y s w e r e e s s e n t i a l l y fully d e n s e a f t e r e x t r u s i o n . V a r i o u s t h e r m o m e c h a n i c a l t r e a t m e n t s w e r e u s e d in o r d e r to o p t i m i z e p r o p e r t i e s . T h e s e a r e l i s t e d in T a b l e II. The following p r o p e r t i e s w e r e then d e t e r m i n e d : 1) h a r d n e s s a s a function of a n n e a l i n g t e m p e r a t u r e ; 2) t e n s i l e p r o p e r t i e s at r o o m t e m p e r a t u r e , and a s a function of annealing t e m p e r a t u r e ; 3) s t r e s s - t o - r u p t u r e s t r e n g t h s at 400~ 650~ 4) e l e c t r i c a l c o n d u c t i v i t y . RESULTS
AND D I S C U S S I O N
Dendrite a r m spacing is a function of the degree of supercooling I and since the extent of supercooling depends on the cooling rate, one can expect a relationship between dendrite a r m spacing and cooling rate. Experimental evidence available indicates that dendrite a r m spacing in cast aluminum alloys is influenced only by cooling rate (or "local solidification time"). B o w e r et al.2 plotted data obtained from a n u m b e r of investigations with aluminum alloys, showing the relationship between secondary a r m spacing d and local solidifcation time 0f. Of the wide range of solidification rates examined, the dendrite a r m spacing measurements were found to correlate linearly with Of on loglog coordinates: Table I. Alloy Compositions and Fabrication Variables
Alloy
Zr, Wt Pct
Cr, Wt Pct
02, Wt Pct
Cu(bal) Wt Pct
ZA-2 ZA-3 ZA-8 ZAC-I
0.20 0.37 0.80 0.10
0.32
0.04 0.03 0.08 0.04
99.76 99.60 99.14 99.54
Extr. Ratio 25 25 25 25
to to to to
Extr. Temp, ~ 1 1 1 1
600 650 650 650
V O L U M E 3, A P R I L 1 9 7 2 - 8 7 5
d = 7.503 .39
[
T h i s r e l a t i o n s h i p was c o n f i r m e d for a n u m b e r of a l u m i n u m alloys over a wide r a n g e of cooling r a t e s by Matyja e t a l . 3 They plotted d e n d r i t e a r m s p a c i n g as a function of cooling r a t e , and obtained a s i m i l a r l i n e a r c o r e l a t i o n with a s l o p e of 0.32. Such a r e l a t i o n s h i p has b e e n obtained in this work for C u - Z r a l l o y s , F i g . 1. The slope of this c u r v e was found to be g r e a t e r (approximately 0.48) than that o b s e r v e d for a l u m i n u m a l l o y s (0.32). It was found that the m e t a s t a b l e e x t e n s i o n of the solid solubility l i m i t of z i r c o n i u m in copper can be i n c r e a s e d e x t e n s i v e l y by u t i l i z i n g cooling r a t e s of a p p r o x i m a t e l y 107 to 109~ Subsequent s t u d i e s by Ray 4 showed that the s o l u b i l i t y of z i r c o n i u m in copper could
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