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Both m a c r o g r a p h i c e x a m i n a t i o n of the f r a c t u r e d s u r f a c e s and m e t a l l o g r a p h i c e x a m i n a t i o n of s e c t i o n e d s p e c i m e n s r e v e a l e d s t r u c t u r a l d e t a i l s . In plated s p e c i m e n s l a r g e voids were noted b e t w e e n rows of f i b e r s , and the i n t e r f i b e r spacing was f o r c i b l y i n c r e a s e d . The e l e c t r o p l a t e d s i l v e r was deposited in a c o n c e n t r i c m a n n e r , and fine p o r e s were n o t i c e d in the form of r i n g s . Both hot p r e s s e d and s i n t e r e d and cold p r e s s e d and s i n t e r e d s p e c i m e n s showed e x c e l l e n t m e c h a n i c a l bonding b e t w e e n the s i l v e r and the rough s u r f a c e s of the f i b e r s . F r a c t u r e s u r f a c e s were c r i t i c a l l y e x a m i n e d with a 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 e . Two m a j o r types of f i b e r f a i l u r e s were o b s e r v e d : 1) ductile f a i l u r e with r e d u c t i o n s in a r e a s as g r e a t a s 50 to 60 pct (the f r a c ture s u r f a c e showed the highly d i s t o r t e d and elongated t u n g s t e n g r a i n s in the f o r m of r e e d s ) ; and 2) b r i t t l e f r a c t u r e s were the usual types of f a i l u r e (the f a i l u r e m e c h a n i s m was by cleavage of the s u r f a c e and was noted to have fine p a r t i c l e s of p r e s u m a b l y b r o k e n t u n g s t e n c r y s t a l s on the f r a c t u r e d s u r f a c e , b u t there was no r e d u c t i o n in area). The f r a c t u r e s u r f a c e s r e v e a l e d e x t e n s i v e dimple f r a c t u r e of the s i l v e r m a t r i x , smooth pore i n t e r i o r s with v e r y fine s t r a i n m a r k i n g s , s e p a r a t i o n of g r a i n b o u n d a r i e s due to s t r a i n , and e x c e l l e n t bonding b e tween the s i l v e r and the t u n g s t e n f i b e r s u r f a c e .
AC KNOWLEDGMENT G r a t e f u l thanks a r e due to M r . R i c h a r d Schmidt of the Naval Air S y s t e m s C o m m a n d , Washington, D.C. for his e n c o u r a g e m e n t and s u p p o r t of this work. The help of Dr. O. Johari in taking the s c a n n i n g e l e c t r o n m i c r o g r a p h s is gratefully acknowledged.
REFERENCES 1. A. Kellyand G. J. Davies:Met. Rev., 1965,vol.10, pp. 1-77. 2. G. D. McAdam:J. Iron SteetInst., 1951,vol. 168,pp. 346-58. 3. L. J. Cohenand O. Ishai:J. CompositeMater., 1967,vol. 1, pp. 390-403. 4. G. A. Cooper:J. Mech. Phys. Solids, 1966,vol. 14, p. 103.
C o r r e c t i o n to M e t . T r a n s . , 1970, col. 1 D i s c u s s i o n by M. C. Jha and A. K. L a h i r i of " A Study of the F a c t o r s Which Influence the Rate M i n i m u m P h e n o m e non d u r i n g Magnetite R e d u c t i o n . " A u t h o r s ' Reply by P. K. Strangway and H. U. Ross. Page 335, Column 1, L i n e 1 Change Strangeway to Strangway. Page 336, Line 6 of A u t h o r s ~ Reply The p h r a s e " b u t not i n h e m a t i t e b r i q u e t t e s " was o m i
