Fisheyes in rolled steel exposed to hydrogen at room temperature
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AlloyDesignation
CCoAI* CE*
Cco* WCoAI~PCo~PCoAI~ VCoAI82
Newlyestablished 81 90 90,48 93.11 0.2346 7~92 6.90 eutectac Newestablished 82.54 90.21 93.28 0.2858 7.96 6,94 eutectic-withmexperimentalerror to
26.0
31.5
maxlInlze VCoAI
Newlyestablished 81.26 90.75 92.94 0.1875 7.92 6,86 eutecac-w~tlm~experimentalerror to minimizeVCoAI Previouslyaccepted 89.0 90.0 92.0 0.6667 7,82 7.43 eutectlc
21.0
67 8
VcoAlas measuredexperimentally= 29 5 -+2 pct. *Compositionsin wt pct cobaltof CoAl,eutectm,or Co sohdsolutmn. tWelghtfractionof CoAlin a eutecticalloy. ~Densities(in gr/cm3) of constituentphases. '~Volumepct of CoAlin eutecnc. r e c t i o n a l l y s o l i d i f i e d 89 wt pct a l l o y which, a c c o r d ing to the p r e v i o u s l y published d i a g r a m , should have b e e n s i n g l e phase CoAl at the e u t e c t i c t e m p e r a t u r e . As can be s e e n , however, the m i c r o s t r u c t u r e is r e p r e s e n t a t i v e of an o f f - e u t e c t i c d i r e c t i o n a l l y s o l i d i fied alloy; the c o a r s e n e s s of the Co phase can only be a t t r i b u t e d to it f o r m i n g d u r i n g a liquid to s o l i d and not a solid to solid t r a n s f o r m a t i o n . F u r t h e r m o r e , the new c o m p o s i t i o n s c l o s e l y c o r r e s p o n d to the volu m e f r a c t i o n s of the p h a s e s e x p e r i m e n t a l l y o b s e r v e d . T h e newly r e p o r t e d c o m p o s i t i o n s can be c o n v e r t e d to volume f r a c t i o n s provided the l a t t i c e p a r a m e t e r s (and, t h e r e f o r e , d e n s i t i e s ) of the i n d i v i d u a l p h a s e s a r e known. Luo and Duwez 9 have m e a s u r e d l a t t i c e p a r a m e t e r s of r a p i d l y cooled fcc s t a b i l i z e d CoAl a l loys while the lattice p a r a m e t e r of s t o i c h i o m e t r i c CoAl is well e s t a b l i s h e d , l~ An e s t i m a t e of the l a t tice p a r a m e t e r of o f f - s t o i c h i o m e t r i c CoAl can be made by a s s u m i n g the v a r i a t i o n of effective a t o m i c s i z e with A1 content is the s a m e a s that o b s e r v e d in the cobalt solid solution. On p e r f o r m i n g t h e s e a n a l y s e s , s u m m a r i z e d in T a b l e I, the v o l u m e f r a c tion of the CoAl phase, b a s e d on the quoted a c c u r a c y in the i n v a r i a n t c o m p o s i t i o n s , should be 26.0 ~ ~5 pct which c o m p a r e s quite well with the m e a s u r e d v a l u e of 29.5 • 2 pct. In c o n t r a s t , the v o l u m e f r a c t i o n of CoAl should be 67.8 pct b a s e d on the p r e v i o u s l y r e p o r t e d c o m p o s i t i o n s (cf. T a b l e I). T h u s , it can be concluded that the c o m p o s i t i o n s r e p o r t e d h e r e i n a r e c o n s i d e r a b l y c l o s e r to the t r u e i n v a r i a n t c o m p o s i t i o n s than those r e p o r t e d p r e v i o u s l y . We a r e indebted to Sonny E. Knight for a s s i s t a n c e in the o r i g i n a l setup for o u r EDAX a n a l y s i s . T h i s work was s u p p o r
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