The identification of second phases within bubbles in annealed doped tungsten wire
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S E V E R A L
i n v e s t i g a t i o n s of h e a v i l y - w o r k e d doped t u n g s t e n have d e m o n s t r a t e d that its highly c r e e p - r e s i s t a n t , r e c r y s t a l l i z e d s t r u c t u r e is due to the p r e s e n c e of r o w s of a d i s p e r s e d s e c o n d p h a s e a l i g n e d p a r a l l e l to the d i r e c t i o n of d e f o r m a t i o n . 1-4 C o n v i n c i n g e v i d e n c e h as b e e n p r e s e n t e d that t h e s e r o w s a r e c o m p o s e d of b u b b l e s , f o r m e d and s t a b i l i z e d by a v o l a t i l e m a t e r i a l within t h e m . 2-6 The o b s e r v a t i o n of m o v i n g liquid within such b u b b le s at n e a r - a m b i e n t t e m p e r a t u r e s s t r o n g l y s u g g e s t s that this m a t e r i a l is p o t a s s i u m . 7 This deduction is s u p p o r t e d by the o b s e r v a t i o n of d i s c r e t e a r e a s of p o t a s s i u m on f r a c t u r e s u r f a c e s of r e c r y s t a l l i z e d doped t u n g s t e n r o d by s e c o n d a r y - i o n m a s s s p e c t r o s c o p y , a The p r e s e n t i n v e s t i g a t i o n p r o v i d e s f u r t h e r c o n f i r m a t i o n that p o t a s s i u m is r e s p o n s i b l e f o r the f o r m a t i o n of the bubble r o w s in a n n e a l e d doped tungsten w i r e , u t i l i z i n g s e l e c t e d a r e a e l e c t r o n d i f f r a c t i o n f r o m thin f o i l s . Some p r e l i m i n a r y r e s u l t s of this study have b e e n p r e v i o u s l y r e p o r t e d f l
EXPERIMENTAL
w e r e u t i l i z e d f o r this i n v e s t i g a t i o n . This w i r e had b e e n p r o c e s s e d f r o m ingots s i n t e r e d in h y d r o g e n at a p p r o x i m a t e l y 3000~ by s t a n d a r d m a n u f a c t u r i n g p r o c e d u r e s . 1~ Short l en g t h s of both w i r e s i z e s w e r e a n n e a l e d by s e l f - r e s i s t a n c e h eat i n g at 3020~ f o r 6 min. in d r y h y d r o g en . O t h er s p e c i m e n s of the 0.18 m m w i r e w e r e f u r n a c e a n n e a l e d at 2250~ f o r one h in a v a c u u m of < 10 -s m m Hg. A c h e m i c a l a n a l y s i s c h a r a c t e r i s t i c of both a s - w o r k e d w i r e s is g i v e n by T a b l e I. Thin f o i l s w e r e p r e p a r e d f r o m longitudinal s e c t i o n s of the a n n e a l e d s p e c i m e n s by e l e c t r o p o l i s h i n g at 20~ in an aq u eo u s solution of s o d i u m h y d r o x i d e and g l y c e r i n e , n Bright field transmission electron micrographs were t ak en at 650 and 100 KV; d a r k f i el d and s e l e c t e d a r e a
PROCEDURE
Two sizes of commercially doped tungsten wire (General Electric Type 218), 2.1 and 0.18 m m diam., Table I. Chemical Analysis of Cleaned, As-Worked Commercially Doped Tungsten Wire
Element
Wt ppm
At ppm
K A1 Si Mo Fe Ni Cu Ca Sr Mn Sn Co Ti O N C H
82 + 2 5+5 4 +2 48 + 2 8 +-1
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