Tensile properties of directionally solidified Al-Si eutectic
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A1-Si e u t e c t i c a l l o y s have been d i r e c t i o n a l l y s o l i d i f i e d in a h o r i z o n t a l r e s i s t a n c e h e a t e d f u r n a c e . The t e m p e r a t u r e g r a d i e n t , G, a h e a d of the s o l i d / l i q u i d i n t e r f a c e was kept f a i r l y c o n s t a n t at 80 C / c m , while the growth r a t e , R, was v a r i e d b e t w e e n 0.28 and 131 p m / s . M i c r o s t r u c t u r a l s t u d i e s show a definite a l i g n m e n t of the r o d - l i k e Si at low growth r a t e s . At growth r a t e s h i g h e r than 14 pan/s the m i c r o s t r u c t u r e s a p p e a r i r r e g u l a r , although s o m e p r e f e r e n t i a l o r i e n t a t i o n of the Si r o d s p a r a l l e l to the growth d i r e c t i o n can be obs e r v e d . T e n s i l e t e s t s show h i g h e r v a l u e s in both y i e l d and u l t i m a t e s t r e n g t h s than was found in p r e v i o u s i n v e s t i g a t i o n s , m o s t l i k e l y due to the c a r e f u l s a m p l e p r e p a r a t i o n p r i o r to t e s t i n g in the p r e s e n t work. The y i e l d s t r e n g t h i n c r e a s e s with the growth r a t e up to about 14 t a n / s , and only a s l i g h t i n c r e a s e is o b s e r v e d at h i g h e r r a t e s . The u l t i m a t e s t r e n g t h a l s o i n c r e a s e s with the g r o w t h r a t e , but shows l e s s t e n d e n c y t o w a r d s a t u r a t i o n . S u p e r p o s i t i o n of h a r d n e s s and y i e l d d a t a show e x c e l l e n t c o r r e l a t i o n , while c o m p a r i s o n b e t w e e n h a r d n e s s and u l t i m a t e s t r e n g t h shows h i g h e r h a r d n e s s than u l t i m a t e v a l u e s with d e c r e a s i n g growth r a t e s .
D I R E C T I O N A L s o l i d i f i c a t i o n of e u t e c t i c a l l o y s has b e e n widely a c k n o w l e d g e d a s a way to i m p r o v e the s t r e n g t h , t h e r m o d y n a m i c s t a b i l i t y , c r e e p and c o r r o s i o n r e s i s t a n c e s of m a t e r i a l s at both r o o m and e l e vated t e m p e r a t u r e s . T h e r e have been n u m e r o u s publ i c a t i o n s on d i r e c t i o n a l s o l i d i f i c a t i o n of e u t e c t i c s in r e c e n t y e a r s , s o m e of which e m p h a s i z e m e c h a n i c a l p r o p e r t i e s and can be found in the p r o c e e d i n g s of s e v e r a l c o n f e r e n c e s . 1-3 T h e m e c h a n i c a l p r o p e r t i e s of d . s . A N S i e u t e c t i c which is an i m p o r t a n t c o m m e r c i a l m a t e r i a l have b e e n r e p o r t e d in s e v e r a l i n v e s t i g a t i o n s , 4"6 but the r e s u l t s d i f f e r f r o m e a c h o t h e r . In t h i s p a p e r we a r e r e p o r t i n g t e n s i l e p r o p e r t i e s of d . s . A 1 - S i e u t e c t i c grown at d i f f e r ent r a t e s . Our r e s u l t s will be c o m p a r e d with t h o s e of the p r e v i o u s i n v e s t i g a t o r s . 4"6 We will a l s o c o m p a r e t h e m w
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