Phase Equilibria in the Be-Al-Fe System Using High-Energy Ion Beams: II
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new a p p r o a c h to the study of the b e r y l l i u m a l u m i n u m - i r o n phase d i a g r a m , we r e c e n t l y r e p o r t e d s e v e r a l of the two and t h r e e - p h a s e points about the a - B e phase as obtained u s i n g high e n e r g y ion beams.1 That work, which will be r e f e r r e d to as MS-I, was motivated by the need for a b e t t e r u n d e r s t a n d i n g of the b e h a v i o r of dilute a l u m i n u m and i r o n i m p u r i t i e s in c o m m e r c i a l b e r y l l i u m . Room t e m p e r a t u r e ion i m p l a n t a t i o n of a l u m i n u m a n d / o r i r o n into b e r y l l i u m was used to c r e a t e a s u p e r s a t u r a t e d solution within the f i r s t ~-0.1 /zm of a b e r y l l i u m host, and the comp o s i t i o n of this r e g i o n was t a i l o r e d to c o r r e s p o n d to points of i n t e r e s t on the phase d i a g r a m . A n n e a l i n g then caused p r e c i p i t a t i o n of one or two second p h a s e s
in the o~-Be, and the solid solubilities of aluminum and iron in beryllium for the particular multiphase equilibrium were determined by ion backscattering analysis. The beryllium-rich region of the berylliumaluminum-iron phase diagram is shown schematically in Fig. I, highly distorted so as to exhibit all of the p e r t i n e n t b o u n d a r i e s . By u s i n g the above t e c h n i q u e s , the points n u m b e r e d 1, 2, and 3 were obtained in MS-I.' (The hcp phase of n o m i n a l c o m p o s i t i o n FeBe11, which was labeled 7 in MS-I, is h e n c e f o r t h t e r m e d X. T h i s change is i n t r o d u c e d to avoid confusion with 7-Fe.) The p r e s e n t study is an e x t e n s i o n of MS-I, m o s t notably to phase b o u n d a r i e s other than those which e n c l o s e the a - B e field of the phase d i a g r a m . The specific o b j e c t i v e s were to d e t e r m i n e point No. 4 in F i g . 1 and to m e a s u r e the a l u m i n u m to i r o n r a t i o s at points No. 5 and 6. The l a t t e r two i n t e r s e c t i o n s r e f l e c t the composition e x t r e m e s of the t e r n a r y 5 phase when it coexists with a - B e . Knowledge of t h e s e l i m i t s is i m p o r t a n t b e c a u s e the v e r y stable 5 phase s e r v e s to tie up a l u m i n u m as an i n t e r m e t a l l i c compound, t h e r e b y p r e v e n t i n g it f r o m e x i s t i n g as a lowm e l t i n g component at g r a i n b o u n d a r i e s which r e d u c e s s t r e n g t h and d u c t i l i t y . While o b s e r v e d v a r i a t i o n s in the lattice p a r a m e t e r of 5 have b e e n taken as evidence
of an a p p r e c i a b l e c o m p o s i t i o n range, 2 this r a n g e had not p r e v i o u s l y b e e n d e t e r m i n e d . 1. E X P E R I M E N T A L PROCEDURE Single c r y s t a l s of e l e c t r o p o l i s h e d b e r y l l i u m , with t y p i c a l d i m e n s i o n s of 10 )< 10 • 3 ram, were used as hosts for the i m p l a n t a t i o n e x p e r i m e n t s . The l a r g e face was p e r p e n d i c u l
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