Strengthening of copper with tantalum (continuous) filaments
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S c = S f V f + (~n(1 - Vf)Vf > Vmin
[1]
where S c = the ultimate t e n s i l e s t r e n g t h of the c o m posite; Sf = u l t i m a t e t e n s i l e s t r e n g t h of the f i l a m e n t ; V f = volume f r a c t i o n of the f i l a m e n t ; g~n = s t r e s s in the m a t r i x at the s t r a i n ef at which the f i l a m e n t s r e a c h e d Sf, and Vmin is the volume f r a c t i o n of the f i l a m e n t which m u s t be exceeded before the s t r e n g t h e n i n g can occur. However, in the ductile fiber ( c o n t i n u o u s ) - d u c tile m a t r i x s y s t e m s like s t e e l - s i l v e r , 4 W-Cu (250~ s M o - C u , t u n g s t e n - b r a s s (90-10), 6 the e x p e r i m e n t a l v a l ues of the t e n s i l e s t r e n g t h s of the c o m p o s i t e s have a l ways been found to be higher than those p r e d i c t e d by Eq. [1]. Also, these c o m p o s i t e s f r a c t u r e d at a s t r a i n much l a r g e r than the f r a c t u r e s t r a i n of the f i l a m e n t s . F r o m his work on s t e e l - s i l v e r c o m p o s i t e s , P i e h l e r 4 explained this to be due to a h y d r o s t a t i c component of s t r e s s which could a r i s e from the l a t e r a l s t r e s s e s exe r t e d by the d e f o r m i n g m a t r i x which p r o v i d e d a r e s t r a i n t to continued n e c k i n g of the f i l a m e n t s . R e c e n t l y , Schoene 6 c o n f i r m e d this by his s t u d i e s on the W-(90-10) b r a s s c o m p o s i t e s in which, by d i s s o l v i n g a p a r t of the m a t r i x , the s u c c e s s i v e i n t e r n a l necking of the t u n g s t e n f i l a m e n t s , even r e m o t e from the f r a c t u r e s u r f a c e , was d e m o n s t r a t e d . To gain f u r t h e r insight into the b e h a v i o r of ductile f i l a m e n t - d u c t i l e m a t r i x s y s t e m , i n v e s t i g a t i o n s on the c o m p o s i t e s of T a f i l a m e n t - C u which r e p r e s e n t a ductile f i l a m e n t - d u c t i l e m a t r i x s y s t e m f a b r i c a t e d by the i n f i l t r a t i o n technique were conducted, the r e s u l t s of which a r e r e p o r t e d in the following. E X P E R I M E N T A L PROCEDURE Materials O x y g e n - f r e e high purity grade copper was p r o c u r e d f r o m Utility B r a s s and Copper Corp., N . J . , in the form of an ~-~ in. diam rod which was cut into s l u g s of des i r e d lengths. They were m e c h a n i c a l l y c l e a n e d p r i o r to loading in the mold. IQBAL AHMAD and J. M. BARRANCOare Chief, Physical Chemistry Laboratory and Physical Metallurgist,respectively, Maggs Research Center, U.S. Army WatervlietArsenal, Watervliet,N. Y. Manuscript submitted June 2, 1969. METALLURGICALTRANSACTIONS
F i l a m e n t s of high p u r i t y t a n t a l u m with d i a m e t e r s of 0.002, 0.003, 0.005, and 0.010 in. were obtained from the F a n s t e e l M e t a l l u r g i c a l Corp., Chicago Ill. In m o s t of the s p e c i m e n s , a 0.003 in. diam f i l a m e n t was used. A few contained 0.002 in. dia
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