Axial creep and stress-rupture of B-Al composites
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i r s t part involved c r e e p t e s t i n g of u n i a x i a l b o r o n and B o r s i c - 6 0 6 1 a l u m i n u m c o m p o s i t e s at 300 ~ 400 ~ and 500~ The second p a r t involved a study of the f r a c ture m e c h a n i s m in the composite u s i n g light m i c r o scopy and s c a n n i n g e l e c t r o n m i c r o s c o p y . In g e n e r a l , p r e v i o u s work has i n d i c a t e d that B-A1 c o m p o s i t e s behave a s expected, with little or no p l a s tic d e f o r m a t i o n p r i o r to f a i l u r e in the f i l a m e n t axis d i r e c t i o n . S'6 Only v e r y low p l a s t i c s t r a i n s , 0.003 to 0.08 pct, were m e a s u r e d in e x p e r i m e n t s using s t r a i n gages. Although the t e s t s e m p l o y i n g m e c h a n i c a l ext e n s o m e t e r s r e c o r d e d somewhat l a r g e r s t r a i n s the c o n t r i b u t i o n s of grip slippage and outer l a y e r m a t r i x s h e a r to these r e s u l t s have b e e n shown to account for the difference. The r e s u l t s of the p r e v i o u s i n v e s t i g a t i o n s i n d i c a t e d r u p t u r e t i m e s of the o r d e r of 7 to >100 h r for ~45 vol pct B-A1 c o m p o s i t e s t e s t e d at 260~ and 100,000 psi. C r e e p f a i l u r e m e c h a n i s m s have not b e e n explained in detail, although f a i l u r e does e v e n t u a l l y o c c u r with time at t e m p e r a t u r e at s t r e s s e s below the short time UTS at t e m p e r a t u r e . The f a i l u r e o b s e r v a t i o n s which have b e e n d i s c u s s e d in the l i t e r a t u r e will be included in the d i s c u s s i o n s e c t i o n .
EXPERIMENTAL Composite F a b r i c a t i o n . C o m p o s i t e s were f a b r i c a t e d by the p l a s m a - s p r a y m o n o l a y e r tape p r o c e s s , e The t a p e s e m p l o y e d c o n s i s t e d of B o r s i c f i l a m e n t , 0.004 in. n o m i n a l d i a m , wound at 185 t u r n s p e r in., s p r a y e d with 6061 a l u m i n u m alloy m a t r i x . The tapes were hot p r e s s e d in v a c u u m for 1 hr at 550~ and 5500 psi to form c o m p o s i t e p a n e l s 1 by 5 by 0.026 in., five l a y e r s , thick. All B o r s i c f i l a m e n t c o m p o s i t e s contained n o m i n a l l y 50 vol pct f i l a m e n t . A s e r i e s of 37 vol pct b o r o n f i l a m e n t c o m p o s i t e s was also f a b r i c a t e d in o r d e r to c o m p a r e the b o r o n and B o r s i c c o m p o s i t e s , and a l i m VOLUME 1,JANUARY 1970-93
ited n u m b e r of 38 vol pct SiC f i l a m e n t c o m p o s i t e s were a l s o f a b r i c a t e d and t e s t e d . A t r a n s v e r s e c r o s s s e c tion of a B o r s i c - A 1 composite f a b r i c a t e d from p l a s m a -
Fig. 1--Borsic-A1 composite fabricated from plasma sprayed monolayer tapes. Magnification 80 times.
s p r a y e d m o n o l a y e r tapes is shown in Fig. 1. C r e e p and S t r e s s Rupture M e a s u r e m e n t s . C r e e p and s t r e s s - r u p t u r e m e a s u r e m e n t s were made on c o m p o
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