The transverse tensile properties of boron fiber reinforced aluminum matrix composites
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T H E b o r o n - a l u m i n u m c o m p o s i t e s y s t e m is v e r y a t tractive as a structural engineering material because of its o u t s t a n d i n g m o d u l u s and s t r e n g t h r a t i o s . 1 F o r this r e a s o n e n g i n e e r i n g a p p l i c a t i o n s such as t u r b i n e engine fan b l a d e s , 2-4 r e i n f o r c e d stiffened p a n e l s and a i r f r a m e s t r u c t u r a l b e a m s , S have been developed. B o r o n - a l u m i n u m c o m p o s i t e s have a l s o been chosen b e c a u s e of the e x c e l l e n t high t e m p e r a t u r e (600~ p r o p e r t i e s 6 and j o i n a b i l i t y . 7 T h e s e excellent p r o p e r t i e s a r e b a s i c a l l y r e l a t e d to the r e i n f o r c i n g fiber p r o p e r t i e s while the s t r e n g t h in u n r e i n f o r c e d d i r e c t i o n s is m o r e c l o s e l y r e l a t e d to the m a t r i x p r o p e r t i e s . Although a u n i d i r e c t i o n a l 50 pct by v o l u m e b o r o n - a l u m i n u m c o m p o s i t e can exhibit a l o n g i t u d i n a l u l t i m a t e t e n s i l e s t r e n g t h of 200,000 p s i , the t r a n s v e r s e s t r e n g t h is g e n e r a l l y l e s s than o n e - t e n t h of this v a l u e . 1'~'s-ll T h i s is in c o n t r a s t to the r a t i o of a x i a l to t r a n s v e r s e e l a s t i c m o d u l i of l e s s than two to one. A method for c i r c u m v e n t i n g this s t r e n g t h p r o b l e m has been to c r o s s ply l a y e r s of c o m p o s i t e to p r o vide the a x i a l s t r e n g t h of f i b e r s in m o r e than one d i r e c t i o n . T h i s , however, is not a l w a y s a s a t i s f a c t o r y solution b e c a u s e of the r e s u l t a n t c o m p r o m i s e in p r o p e r t i e s . It has been the goal of this i n v e s t i g a t i o n to d e t e r m i n e the t r a n s v e r s e t e n s i l e p r o p e r t i e s of b o r o n a l u m i n u m c o m p o s i t e s and to elucidate c o m p o s i t e f a i l u r e m e c h a n i s m s to p e r m i t the d e v e l o p m e n t of a method for i n c r e a s i n g t r a n s v e r s e s t r e n g t h . Silicon c a r b i d e coated b o r o n f i b e r has b e e n used in this i n v e s tigation p r i m a r i l y b e c a u s e of its g r e a t e r c h e m i c a l s t a b i l i t y than uncoated b o r o n in a l u m i n u m m a t r i c e s ) ~
b o r o n onto a heated t u n g s t e n s u b s t r a t e . F i b e r s p r o duced u s i n g dc and r f heating t e c h n i q u e s w e r e both evaluated. The BORSIC f i b e r is f a b r i c a t e d by d e p o s i t ing a 0.1 to 0.15 m i l coating of s i l i c o n c a r b i d e onto the b o r o n . The s i l i c o n c a r b i d e f i b e r is also p r o d u c e d by deposition onto a t u n g s t e n s u b s t r a t e . The m a t r i x m a t e r i a l s used w e r e a l l a l u m i n u m b a s e a l l o y s . T h r e e heat t r e a t a b l e a l l o y s , 2024, 2219, and 6061 w e r e u s e d a s well a s t h r e e n o n h e a t t r e a t a b l e a l l o y s , 1
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