Self-diffusion in aluminum at low temperatures
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T. R. RAMACHANDRAN
Values of the s e l f - d i f f u s i v i t y of p u r e a l u m i n u m in the t e m p e r a t u r e r a n g e 130 ~ to 200~ have been d e t e r m i n e d by m e a s u r i n g the r a t e of annealing of p r i s m a t i c and faulted d i s l o c a t i o n loops in thin foils of q u e n c h e d 99.999 pct A1 u si n g a d i f f u s i o n - c o n t r o l l e d c l i m b m o d e l due to Sei d m an and Balluffi m o d i f i e d to take into a c c o u n t e l a s t i c i n t e r a c t i o n b e t w e e n v a c a n c i e s and d i s l o c a t i o n s . Changes in line e n e r g y of p r i s m a t i c loops with o r i e n t a t i o n w e r e e v a l u a t e d and found to p r o d u ce a m a x i m u m e r r o r in D of 17 pct. O t h e r p o s s i b l e s o u r c e s of e r r o r w e r e e v a l u a t e d . The r e s u l t s give D = 0.19 + 0.06 exp - ( 1 . 2 8 + 0.04 ev)/kT sq c m p e r s e c . A d i r e c t m e t h o d of d e t e r m i n i n g the a c t i v a t i o n e n e r g y f o r s e l f - d i f f u s i o n f r o m p r i s m a t i c loop an n eal i n g r a t e s is p r e s e n t e d which m i n i m i z e s the e f f e c t s of many s o u r c e s of v a r i a t i o n in individual c l i m b r a t e s .
M E A S U R E M E N T of the a n n e a li n g k i n e t i c s of v o i d s and d i s l o c a t i o n loops in quenched m e t a l s u s in g 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 is a p o w e r f u l m e t h o d of studying v a c a n c y diffusion c h a r a c t e r i s t i c s , enabling d i f f u s i v i t i e s of ~10 -17 sq c m p e r s e c to be r e a d i l y m e a s u r e d . The t e c h n i q u e is p a r t i c u l a r l y u s e f u l f o r t h o s e m a t e r i a l s such as a l u m i n u m in which s t a n d a r d m e t h o d s a r e difficult. T r a c e r m e th o d s of m e a s u r i n g d i f f u s i v i t i e s a r e difficult to apply to a l u m i n u m with the r e s u l t that the data r e l a t i n g to a l u m i n u m s e l f - d i f fusion is l i m i t e d and its r e l i a b i l i t y q u e s t i o n e d . 1-3 N.M.R. t e c h n i q u e s have b e e n u s e d to s u p p l e m e n t t h e s e r e s u l t s . 4-6 The i n t e r p r e t a t i o n of the c o m b i n e d data in t e r m s of diffusion m e c h a n i s m s is the s u b j e c t of c o n t r o v e r s y . 3'7's F u r t h e r a c c u r a t e m e a s u r e m e n t s of a l u m i n u m s e l f - d i f f u s i o n a r e c l e a r l y d e s i r a b l e . Volin and Balluffi 1~ d ed u c e d a l u m i n u m diffusion r a t e s f r o m m e a s u r e d r a t e s of s h r i n k a g e of q u e n c h e d - i n v o i d s and an a s s u m e d value of the s u r f a c e e n e r g y . D i s l o c a t i o n loop an n eal i n g r a t e s can be m e a s u r e d with r a t h e r g r e a t e r p r e c i s i o n b e c a u s e loops a r e u s u a l l y s u b s t a n t i a l l y l a r g e r . A l s o loops a r e not subject to the c o m p l i c a t i n g influence of h y d r o g e n o c c l u s i o n . Loop a n ne al i n g r
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