Direct observation of voids in doped tungsten by scanning electron microscopy
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increased precipitate concentration near longitudinal grain boundaries as observed by other investigators. ~'2'6 This is further evidence that diffusional creep has occurred. 1. R. L. Squires, R. T. Weiner, and M. Phillips: J: Nuel. Mater., 1963, vol. 8 , pp. 77-80. 2. W. Vickers and P. Greenfield: J. Nucl. Mater., 1967. vol. 24, pp. 249-60. 3. B. W. Pickles: J. Inst. Metals, 1967, vol. 95, pp. 333-37. 4 . A. Karim, D. L. Holt, and W.A. Backofen: Trans. TMS-AIME, 1969, vol. 245, pp. 2421-24. 5 . V. J. Haddrelh ,L Nucl. Mater., 1966, vol. 18, pp. 231-32. 6. J. E. Harris, R. B. Jones, G. W. Greenwood, and M.J. Ward: J. Aust. Inst. Metals, 1969, vol. 14, pp. 154-62. 7. A. Karim, D. L. Holt, and W.A. Backofen: Trans. TMS-AIME, 1969, vol. 245, pp. 1131-32. 8 . A. Karim: Ultrafine-Grain Metals, J. J. Burke and Volker Weiss, eds., pp. 295322, Syracuse University Press, Syracuse, N.Y., 1970.
Direct Observation of Voids in Doped Tungsten by Scanning Electron Microscopy G. D A S
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electron microscopy has been e m p l o y e d r e c e n t l y t o c h a r a c t e r i z e t h e s u b s t r u c t u r e of d o p e d a n d u n d o p e d p o w d e r m e t a l l u r g y (PM) t u n g s t e n o f v a r i o u s g e o m e t r i c a l f o r m s s u c h a s w i r e s , 1'2 r o d s ,1'3 s h e e t s ,4 a n d r i b b o n s .5 I n a n n e a l e d P M w i r e s ( 0 . 0 3 in. dicta) and ribbons (0.005 in. thick), a particularly i m p o r t a n t c o n s t i t u e n t of t h e s u b s t r u c t u r e c o n s i s t i n g o f r o w s of c i r c u l a r o r e l l i p t i c a l f e a t u r e s (100 t o 1 0 0 0 A i n d i a m ) l y i n g a l o n g t h e d i r e c t i o n of w o r k i n g h a s b e e n o b s e r v e d 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 a n d i n t e r p r e t e d a s v o i d s .~'5 It h a s b e e n p o i n t e d o u t by i n v e s t i g a t o r s ~'5 that t h e m o r p h o l o g y of t h e e l o n g a t e d g r a i n s t r u c t u r e t o g e t h e r w i t h p r e f e r e n t i a l distribution of extremely s m a l l v o i d s s h o u l d contribute t o the stability of lamp filaments d u r i n g t h e i r perf o r m a n c e . H o w e v e r , no q u a n t i t a t i v e s t u d y h a s b e e n r e p o r t e d y e t . O n e o f t h e p r i n c i p a l difficulties in t h i s G. DAS is Staff Metallurgist, Development Laboratory, IBM Components Division, East Fishkill, Hopewell Junction, N. Y. Manuscript submitted April 2 2 , 1971. METALLURGICAL
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r e s p e c t is t h e l i m i t e d m a t e r i a l a v a i l a b l e f r o m w i r e s o f less t h a n 0 . 0 1 i n . diam f o r p r e p a r a t i o n o f e l e c t r o n transparent s a m p l e s . In c o n t r a s t , 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 y w i t h i t s i n h e r e n t h i g h r e s o l u t i o n a n d d e p t h of f o c u s h a s t h e r e q u i r e d flexibility for handling s p e c i m e n s of v a r i o u s g e o m e t r i e s a n d e x t r e m e l y s m a l l s i z e s . It c a n t h u s be r e a d i l y
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