The recrystallization of heavily-drawn
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B. SNOW
The r e c r y s t a l l i z a t i o n of 0.18 m m doped tungsten w i r e , s w a g e d and d r a w n to a t r u e s t r a i n of 7.7 at t e m p e r a t u r e s of < 0.47 Tin, was i n v e s t i g a t e d by light m i c r o s c o p y and by t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y . The a s - d r a w n s t r u c t u r e of the w i r e c o n s i s t e d of g r e a t l y e l o n g a t e d , r i b b o n - s h a p e d g r a i n s which had a p r o n o u n c e d (110) f i b e r t e x t u r e , T h e s e cont a i n e d w e l l - d e v e l o p e d , e l o n g a t e d c e i l s with few t r a n s v e r s e b o u n d a r i e s . The o n s e t of s u b b o u n d a r y and g r a i n b o u n d a r y m i g r a t i o n , t o g e t h e r with the f o r m a t i o n of p o t a s s i u m - c o n t a i n i n g bubbles in r o w s o r i e n t e d p a r a l l e l to the d r a w i n g d i r e c t i o n , was o b s e r v e d a f t e r a n n e a l i n g at 800~ for 1 h. At h i g h e r t e m p e r a t u r e s , the s p a c i n g and the m i s o r i e n t a t i o n of the l o n g i t u d i n a l s u b b o u n d a r i e s i n c r e a s e d , and new t r a n s v e r s e s u b b o u n d a r i e s w e r e f o r m e d . Both s u b b o u n d a r y and g r a i n b o u n d a r y m~gration w e r e s t r o n g l y i n h i b i t e d by the bubble r o w s , a s w e l l a s by the u n i f o r m i t y of the d e f o r m a t i o n and the w e l l - d e v e l o p e d t e x t u r e . At 2100~ t h e s e m e c h a n i s m s p r o d u c e d a f i n e - g r a i n e d , p a r t i a l l y r e c r y s t a l l i z e d s t r u c t u r e (1.2 ~ m a v e r a g e l o n g i t u d i n a l b o u n d a r y spacing) without change in the d e f o r m a tion t e x t u r e . A t 2150~ and above, l a r g e g r a i n s of high a s p e c t r a t i o , which a l s o r e t a i n e d the (110) d r a w i n g t e x t u r e , w e r e f o r m e d by e x a g g e r a t e d g r a i n growth. T h i s p r o c e s s was i n i t i a t e d by a v e r y s m a l l population of g r a i n s which had a c q u i r e d the n e c e s s a r y s i z e a d v a n t a g e d u r i n g the growth of the f i n e - g r a i n e d s t r u c t u r e .
DURINGthe
p a s t 15 y e a r s , c o n s i d e r a b l e e f f o r t has been devoted to the study of c o m m e r c i a l l y doped t u n g s t e n w i r e due to i t s t e c h n o l o g i c a l i m p o r t a n c e a s an i n c a n d e s c e n t l a m p f i l a m e n t m a t e r i a l . S p e c i a l a t t e n t i o n has b e e n d i r e c t e d t o w a r d the m e c h a n i s m s by which the, r e c r y s t a l l i z a t i o n and s u b s e q u e n t c r e e p r e s i s t a n c e of t h i s m a t e r i a l a r e influenced by s m a l l a m o u n t s of d e l i b e r a t e l y i n t r o d u c e d p o t a s s i u m , s i l i con, and a l u m i n u m (total n o m i n a l l y < 500 at ppm). R e cent s t u d i e s 1-3 have c o n f i r m e d t h a t a n n e a l e d d o p e d t u n g s t e n w i r e , f a b r i c a t e d by s t a n d a r d c o m
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