Reinforcement of magnesium with boron and tantalum filaments
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m a c h i n e d to a d i a m e t e r of 0.5 in. and then cut into m e l t s l u g s of a p p r o p r i a t e lengths. The s l u g s w e r e c h e m i c a l l y c l e a n e d in a 10 p c t s o l u t i o n of n i t r i c acid. FILAMENTS B o r o n f i l a m e n t s (0.004 in. d i a m ) w e r e obtained both f r o m T e x a c o E x p e r i m e n t I n c . , R i c h m o n d , Va., and United A i r c r a f t , E a s t H a r t f o r d , Conn. T a n t a l u m f i l a m e n t s (0.010 in. d i a m ) w e r e p r o c u r e d f r o m F a n s t e e l Metallurgical Corp., Chicago, Ill. These filaments w e r e cut in a p p r o p r i a t e lengths and s t r a i g h t e n e d . T h e y w e r e then p l a c e d in a t a n t a l u m s u s c e p t o r and i n d u c t i v e l y h e a t e d in a v a c u u m of 10 -4 - 10-5 t o r r for 10 m i n at 700~ They e m e r g e d b r i g h t and c l e a n . THE MOLD T h e m o l d was m a d e f r o m high p u r i t y g r a p h i t e o b t a i n e d f r o m U l t r a C a r b o n C o r p . , Bay City, Mich. F A B R I C A T I O N OF COMPOSITES T h e a p p a r a t u s and p r o c e d u r e f o r the i n f i l t r a t i o n t e c h n i q u e u s e d to f a b r i c a t e the s p e c i m e n s had b e e n d e s c r i b e d in d e t a i l e l s e w h e r e 3. The g r a p h i t e m o l d was d e g a s s e d at 1200~ f o r ~ h u n d e r v a c u u m . The f i l a m e n t s , in p r e d e t e r m i n e d length and n u m b e r c o r r e s p o n d i n g to the r e q u i r e d v o l u m e f r a c t i o n , w e r e p l a c e d in the m o l d c a v i t y . The m a g n e s i u m s l u g s w e r e p o s i t i o n e d in the top s e c t i o n . A l o o s e l y fitting g r a p h i t e p i s t o n was a l s o p l a c e d o v e r t h e s e s l u g s . The whole a s s e m b l y was then t r a n s f e r r e d to the i n f i l t r a t i o n e n v e l o p e . The envelope was e v a c u a t e d and b a c k - f i l l e d with p u r i f i e d a r g o n . Heating was by induction. The m e l t i n g of the slug was i n d i c a t e d by the d r o p of the g r a p h i t e piston. The p o w e r was k e p t c o n s t a n t f o r about 3 rain b e f o r e being t u r n e d off. It i s e s t i m a t e d that the t o t a l t i m e f o r which the f i l a m e n t s r e m a i n e d in c o n t a c t with the m o l t e n m e t a l was a p p r o x i m a t e l y 5 m i n . F i g . 1 shows the m o l d b e f o r e and a f t e r infiltration. This fabrication process yielded cast s p e c i m e n s r e a d y for t e s t i n g a f t e r a m i n i m u m of m a c h i n i n g . Depending upon the d e s i g n of the m o l d , gage l e n g t h s b e t w e e n 1 and 2 in. and d i a m e t e r s of 0.12 and 0.25 in. could be obtained. The s o u n d n e s s of the c o m p o s i t e was f i r s t c h e c k e d v i s u a l l y o r with a low m a g n i f i c a t i o n light m i c r o s c o p e , and then by r a d i o g r a p h y . VOLUME 4, MARCH 1973-793
Table I. The AverageYield Strength, Ultimate Tensile Strength, Elastic Modulus, and Elongation of the Fi
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