Segregation to an interface and brittle fracture of metals
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d a t a if t h e s e c o n d law of t h e r m o d y n a m i c s sidered, for
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L i a h a s a r g u e d t h a t ASo, w h i c h i s t h e c h a n g e in e n t r o p y a t 0~ is z e r o (the t h i r d law of t h e r m o d y n a m i c s ) . F r o m e x p e r i m e n t s it s h o u l d b e p o s s i b l e to m e a s u r e (~AH/OT)r* a n d (8Ab/OT)T* but t h e r e is a n e x p e r i m e n t a l l i m i t a t i o n in t e r m s of t h e t e m p e r a t u r e r a n g e o v e r w h i c h it i s p o s s i b l e to m e a s u r e AH a t c o n s t a n t 7 " . T h i s l i m i t a t i o n g e n e r a l l y is d u e to t h e l i m i t e d s t r a i n rate range over which measurements may be cond u c t e d . T h e r e h a v e b e e n a few m e a s u r e m e n t s of Ah' v s T a t c o n s t a n t r * a n d A b vs T a t c o n s t a n t r* a s s h o w n in F i g s . 1 to 3. It c a n b e s e e n t h a t AH i s i n d e p e n d e n t of t e m p e r a t u r e o v e r t h e t e m p e r a t u r e r a n g e i n v e s t i g a t e d , t h e r e f o r e , t h e c h a n g e in AS m u s t b e z e r o in t h i s t e m p e r a t u r e r a n g e . A l s o , A b i s i n d e p e n d e n t of t e m p e r a t u r e o v e r a g i v e n t e m p e r a t u r e r a n g e , F i g . 3, a n d a g a i n t h e c h a n g e in AS d u e to a c h a n g e in 7" m u s t be zero. In o r d e r to d e t e r m i n e AS it i s n e c e s s a r y to c o n s i d e r E q . [4]. H o w e v e r , d u e to t h e e x p e r i m e n t a l l i m i t a t i o n s it is n o t p o s s i b l e to d i r e c t l y d e t e r m i n e AS. If t h e d a t a in F i g . 2 i s c o n s i d e r e d , w h i c h s h o w s t h a t (OH/O T)r* is z e r o in a l l t h e t e m p e r a t u r e r a n g e s i n v e s t i g a t e d , t h e r e f o r e , it is l o g i c a l to a s s u m e t h a t b e t w e e n 0 ~ to 77~ (OH~aT)r* w i l t b e z e r o . If t h i s a s s u m p t i o n i s e m p l o y e d t h e n ~.S is z e r o . F r o m the a n a l y s i s of t h e available data AH = AG, o r if t h e s c a t t e r in t h e d a t a is c o n s i d e r e d t h e n ~ S c a n have a small negative or positive value. This experimental observation would suggest that the assumption m a d e by S c h o e c k is v a l i d , f o r h i s m o d e l p r e d i c t s a s i n a i [ T.~S. S i n c e A H ~ A G , t h i s f a c i l i t a t e s t h e c o m p a r i s o n of e x p e r i m e n t a l a n d c a l c u l a t e d a c t i v a t i o n p a MkTALLURGICAL TRANSACTIONS
r a m e t e r s a s s o c i a t e d w i t h p l a s t i c d e f o r m a t i o n in t h e above examined materials. T h e a u t h o r w i s h e s to a c k n o w l e d g e t h e h e l p f u l d i s c u s s i o n s w i t h D r s . J . C. M. L i a n d U. F . K o c k s . T h i s w o r k w a s s u p p o r t e d by t h e U n i t e d S t a t e s A t o m i c E n e r g y C o m m i s s i o n u n d e r C o n t r a c t No. A T - 4 0 - 1 - 3 6 1 2 . " 1. R. Becker:
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