Copper diffusion in iron during high-temperature tensile creep
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c e n t s t u d i e s1'2 o f t h e e m b r i t t l e m e n t of p u r e i r o n by l i q u i d c o p p e r a t e l e v a t e d t e m p e r a t u r e s ( > 0 . 7 Tm o f i r o n ) , i t w a s a p p a r e n t that t h e m o s t i m p o r t a n t p a r a m e t e r s g o v e r n i n g t h e s e v e r i t y of t h e e m b r i t t l e m e n t i n c l u d e d : t h e dihedral a n g l e o f t h e copper-rich p h a s e at t h e a u s t e n i t e g r a i n b o u n d a r i e s ; t h e s o l u b i l i t y of c o p p e r i n a n s t e n i t e ; a n d t h e d i f f u s i v i t y o f c o p p e r a l o n g aust e n i t e g r a i n boundaries. S a l t e rs f o u n d a d i s t i n c t m i n i m u m v a l u e f o r t h e d i h e d r a l a n g l e at about 1150°C. A t this temperature t h e r e w a s a m a r k e d i n c r e a s e in t h e a m o u n t o f c o p p e r - r i c h p h a s e w h i c h w a s insoluble in a u s t e n i t e . M e a s u r e m e n t s of d i h e d r a l a n g l e a n d i n t e r f a c i a l e n e r g y f o r t h e F e - C u s y s t e m h a v e b e e n m a d e by V a n V l a c k .4 A t 1 1 0 5 ° C , t h e g r a i n b o u n d a r y e n e r g y 7austenite//Taustenite w a s c a l c u l a t e d t o be 850 e r g s p e r sq c m , w h i l s t t h e i n t e r f a c i a l e n e r g y 7 l i q u i d copper//Toustenite__ w a s c a l c u l a t e d t o be 430 e r g s p e r sq c m , c o n f i r m i n g t h a t l i q u i d c o p p e r does l o w e r t h e interracial e n e r g y of austenite g r a i n s . S e v e r a l w o r k e r s5,~ h a v e f o u n d t h a t i n a u s t e n i t e t h e d i f f u s i o n of c o p p e r i s i n t e r g r a n u l a r a t t e m p e r a t u r e s less t h a n l l 0 0 ° C a n d f r o n t a l at t e m p e r a t u r e s g r e a t e r than ll00°C. In the p r e s e n t w o r k , the relative amounts of g r a i n b o u n d a r y a n d s u r f a c e d i f f u s i o n of l i q u i d c o p p e r d u r i n g c r e e p have been determined for notched iron s p e c i mens containing different notch depths of copper. D i h e d r a l a n g l e s o f t h e copper-rich p h a s e at t h e p r i o r a n s t e n i t e g r a i n b o u n d a r i e s were m e a s u r e d f r o m s e l e c t e d c r e e p specimens. A comparison has been made of t h e s e m e a s u r e m e n t s w i t h t h e f r e e s u r f a c e w e t t i n g o f a u s t e n i t e by l i q u i d c o p p e r t h r o u g h s e s s i l e d r o p e x p e r i m e n t s , w h i c h d e t e r m i n e d t h e c o n t a c t a n g l e of d r o p l e t s a s a f u n c t i o n of t i m e a n d t e m p e r a t u r e .
1) P R O C E D U R E T h e experimental w o r k , part of w h i c h has been des c r i b e d e l s e w h e r e ,1 w a s c a r r i e d o u t a s o u t l i n e d . R. R. HOUGH and R. ROLLS are Research Assistant and Lecturer, respectively, Department of Metallurgy, University of Manchester Institute of Science and Technology,Manchester, United Kingdom. Manuscript submitted March 2 2 , 1971. METALLURGICAL
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