Diffusion in a unidirectional filament reinforced metal composite
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W. HERR~G
AND
DARREL
R. TENNEY
A t h e o r e t i c a l a n a l y s i s has been developed to d e s c r i b e c o m p o s i t i o n c h a n g e s r e s u l t i n g f r o m e x p o s u r e of a u n i d i r e c t i o n a l f i l a m e n t r e i n f o r c e d m e t a l composite to an e l e v a t e d t e m p e r a t u r e e n v i r o n m e n t . The a n a l y s i s was b a s e d on a s i m p l e s u p e r p o s i t i o n of f i n i t e - d i f f e r e n c e solutions of the diffusion equation, and was applicable to the case for which the f i l a m e n t and m a t r i x m e t a l s c o m p r i s e d an i s o m o r p h o u s b i n a r y alloy s y s t e m . The p o s s i b i l i t y of c h e m i c a l r e a c t i o n between f i l a m e n t s and m a t r i x was excluded. E x c e l l e n t a g r e e m e n t was o b t a i n e d b e tween c a l c u l a t e d c o n c e n t r a t i o n p r o f i l e s and r e s u l t s of q u a n t i t a t i v e e l e c t r o n m i c r o p r o b e a n a l y s e s of nickel f i l a m e n t r e i n f o r c e d copper s a m p l e s . However, the a g r e e m e n t was found to be quite s e n s i t i v e to the dependence of diffusivity on c o n c e n t r a t i o n . I F m e t a l m a t r i x c o m p o s i t e s a r e placed in e l e v a t e d t e m p e r a t u r e s e r v i c e for extended d u r a t i o n s , t h e r e will be i n t e r a t o m i c diffusion between f i l a m e n t s and m a t r i x . T h i s may cause a d e g r a d a t i o n of c o m p o s i t e p r o p e r t i e s which wilt v a r y in s e v e r i t y depending on the d e s i g n e n v i r o n m e n t and the n a t u r e of the m a t e r i a l s . Diffusion m a y r e s u l t in s i m p l e dilution of c o m p o n e n t s , c o m p l e x i n t e r m e t a l l i c r e a c t i o n s at i n t e r f a c i a l b o u n d a r i e s , or a c o m b i n a t i o n of these two effects. This p a p e r r e p o r t s the r e s u l t s of a r e s e a r c h p r o g r a m to p r o v i d e a m e a n s for p r e d i c t i n g the extent to which diffusion has r e s u l t e d in dilution of c o m p o n e n t s . The i n v e s t i g a t i o n w a s conceived and conducted a s an i n i t i a l a p p r o a c h to the o v e r a l l p r o b l e m of diffusion in f i l a m e n t a r y c o m p o s i t e s , and the p o s s i b i l i t y of i n t e r f a c i a l c h e m i c a l r e a c t i o n was d e l i b e r a t e l y excluded to s i m p l i f y the a n a l y t i c a l p r o c e d u r e . C o m p u t e r i z e d c a l c u l a t i o n s w e r e made, b a s e d on e x i s t i n g diffusion t h e o r y , which w e r e capable of m a p p i n g the c o m p o s i t i o n a l topography of an i d e a l i z e d c o m p o s i t e as a function of t i m e and t e m p e r a t u r e . The model c o m p o s i t e contained m e t a l f i l a m e n t s chosen so that the r e i n f o r c e m e n t m e t a l and the m a t r i x m e t a l c o m p r i s e d an i s o m o r p h o u s b i n a r y s y s t e m . E x p e r i m e n t a l v e r i f i c a t i o n of the p r
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