Porosity and anomalous recrystallization behavior in doped tungsten wire
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1900~ O t h e r s a m p l e s w e r e a n n e a l e d at 1300~ for 1 and 10 hr, and at 2100~ for 1 hr. The m i c r o s t r u c t u r a l c h a n g e s a p p a r e n t f r o m light m i c r o s c o p y w e r e c o r r e lated with m i c r o h a r d n e s s changes following these t r e a t . merits. Since it has been shown 7 that p r i o r r e c o v e r y a n n e a l ing at low t e m p e r a t u r e s can r a i s e the t e m p e r a t u r e f o r r e c r y s t a l l i z a t i o n , t w o - s t e p heat t r e a t m e n t s w e r e c o n ducted to d e t e r m i n e if this effect was s i g n i f i c a n t enough to a l t e r or s u p p r e s s the a n o m a l o u s r e c r y s t a l l i z a t i o n . W i r e s w e r e p r e a n n e a l e d at 500 ~ 800 ~ o r l l 0 0 ~ for 1 h r followed by a n n e a l s at t e m p e r a t u r e s in the range w h e r e core r e c r y s t a l l i z a t i o n n o r m a l l y o c c u r r e d . Supp r e s s i o n of the r e c r y s t a l l i z a t i o n r e a c t i o n was also a t t e m p t e d by the u s e of p r i o r heat t r e a t m e n t at t e m p e r a t u r e s above the a n o m a l o u s r e c r y s t a l l i z a t i o n t e m p e r a t u r e r a n g e , w h e r e the f i b r o u s m i c r o s t r u c t u r e was s t i l l retained. In addition to the u s e of optical m i c r o s c o p y , s p e c i m e n s heated to 1550~ for 3 h r (core r e c r y s t a l l i z e d ) , and at 1700~ f o r 3 h r (core fibrous) w e r e e x a m i n e d by two e l e c t r o n m i c r o s c o p i c a l r e p l i c a m e t h o d s . In one method, s the w i r e s a m p l e was m e c h a n i c a l l y polished to r e v e a l a l o n g i t u d i n a l s e c t i o n and then c h e m i c a l l y etched a f t e r which a c o n v e n t i o n a l t w o - s t a g e P a r l o d i o n c a r b o n r e p l i c a , shadowed with p l a t i n u m , was p r e p a r e d . 9 A second method e m p l o y e d a f r a c t o g r a p h i c r e p l i c a t i o n technique i n v o l v i n g c r i t i c a l shadowing to d i s t i n g u i s h between e l e v a t i o n s and d e p r e s s i o n s on a f r a c t u r e plane. B r i e f l y d e s c r i b e d , this was a o n e - s t a g e c a r b o n r e p l i c a p r e s h a d o w e d with p l a t i n u m at an oblique a n g l e . The p l a t i n u m shadow was applied d i r e c t l y to the f r a c t u r e d s u r f a c e of the s a m p l e and then a c a r b o n r e p l i c a was v a c u u m - d e p o s i t e d . In this technique the shadow of a r a i s e d f e a t u r e on a plane f a l l s outside the b o u n d a r y of the f e a t u r e . However, the shadow of a d e p r e s s e d f e n -
Table I, Chemical Analysis of 0.010 in. Diam Doped Tungsten Wire
Element
Analysis,ppm
K A1 Ca Fe Mg Ni Si
92 4.1 1.5 16
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