X-ray study of the decomposition of metastable Al-rich Al-Fe solid solutions
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T H E t e c h n i q u e of r a p i d quenching of m e t a l s f r o m the liquid s t a t e developed by Duwez, W i l l e n s and K l e m e n t ~ has led to the f o r m a t i o n of new a m o r p h o u s and c r y s t a l line m e t a s t a b l e p h a s e s and a n e x t e n s i o n of s o l i d - s o l u b i l i t y l i m i t s in m a n y alloy s y s t e m s . Using ra~pid quenching t e c h n i q u e , Matyja, G i e s s e n and G r a n t , T o n e j c and Bonefa~id, 3 and J o n e s 4 have i n v e s t i g a t e d b i n a r y a l l o y s of a l u m i n u m with i r o n , Fig. 1. Matyja e t a l . w e r e c o n c e r n e d with the r e l a t i o n s h i p b e tween d e n d r i t e s i z e and cooling r a t e in A I - 1 at. pct F e a l l o y s , w h i l e T o n e j c and Bonefa~id p u b l i s h e d the l a t t i c e p a r a m e t e r s of m e t a s t a b l e s u p e r s a t u r a t e d A 1 - F e solid s o l u t i o n s up to 4.4 at. pct F e . J o n e s found that A 1 - F e a l l o y s , c o n t a i n i n g 4 to 20 wt pct F e , r a p i d l y solidified by the splat cooling t e c h n i q u e , c o n t a i n two d i f f e r e n t z o n e s , zone A and zone B . Zone A c o r r e s p o n d s to a n A 1 - F e s u p e r s a t u r a t e d solid s o l u t i o n , while zone B r e v e a l e d the m e t a s t a b l e A16Fe p h a s e . T h i s p h a s e w a s o b s e r v e d p r e v i o u s l y only in c o n t i n u o u s l y c a s t A1-2 wt pct F e B and in A1-1 wt pct F e 7 solidified with a cooling r a t e m o r e than 3~ p e r sec -1. A16Fe has a n o r t h o r h o m b i c (Ccmm) s t r u c t u r e and is i s o m o r p h o u s with o t h e r A18M type p h a s e s (AlsMn,8' 9 A16(Mn, Fe), 8 AI~(Mn, F e , Cu), 8 Al~Tc a n d A16Rel~ The l a t t i c e p a r a m e t e r s of a l l t h e s e compounds a r e w i t h i n +1.5 pct of 6.51, 7.55 and 8.90A. J o n e s a l s o c o n f i r m e d the r e s u l t s of T o n e j c and Bonefa~id about l a t t i c e p a r a m e t e r s of A 1 - F e solid s o l u t i o n s . In e x a m i n i n g the b e h a v i o r of a n A 1 - F e solid s o lution c o n t a i n i n g about 4 at. pct F e , and a f t e r a n n e a l i n g for a n hour at t e m p e r a t u r e s of up to 600~ J o n e s found that the solid s o l u t i o n d e c o m p o s e d at b e t w e e n 300 ~ and 400~ The A16Fe p a t t e r n b e c a m e d e t e c t a b l e at 400~ and in both zones was r e p l a c e d by A13Fe at 500 ~ and 600~ The p r e s e n t p a p e r g i v e s d e t a i l e d i n f o r m a t i o n on d e c o m p o s i t i o n of s u p e r s a t u r a t e d A1-3.6 at. pct F e solid solution d u r i n g i s o c h r o n a l and i s o t h e r m a l a n n e a l i n g . The s t a b i l i t y of m e t a s t a b l e A16Fe p h a s e and s o m e a s pects of the " t w o - p i s t o n " r a p i d cooling t e c h n i q u e a r e also d i s c u s s e d . A. TONEJC is Assistant in Physical Metallurgy, Institute of Physics of the University of Zagreb, Zagrcb, Yugoslavia. Manuscript submitted July 7, 1970. METALLURGICALTRANSACTIONS
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