Dislocation production in alpha Fe-C alloys by rapid heating
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D I S L O C A T I O N loops a r e o b s e r v e d in r e l a t i v e l y p u r e ~ - F e after neutron irradiation, 1 intense electron i r r a diation, 2 ion b o m b a r d m e n t , 3 and cold work. 4'~ With the exception of the i o n - b o m b a r d e d iron, the p r i s m a t i c loops so f o r m e d lie on {111} p l a n e s with B u r g e r s v e c t o r s in 4111) d i r e c t i o n s and have a round or e l l i p t i c a l shape. Iron ion b o m b a r d m e n t p r o d u c e s s q u a r e - s h a p e d , e d g e - t y p e loops lying on {100} p l a n e s with s i d e s p a r a l l e l to 4100) d i r e c t i o n s . In c o n t r a s t to many other m e t a l s , only a few isolated d i s l o c a t i o n loops can be s e e n in p u r e i r o n a f t e r quenching f r o m a high t e m p e r a t u r e in the c~ r e g i o n , r S e c o n d - p h a s e p a r t i c l e s or i n c l u s i o n s c o n t a i n e d in an o t h e r w i s e d e f e c t - f r e e i r o n lattice can act as i n t e r n a l s o u r c e s for the g e n e r a t i o n of d i s l o c a t i o n s . Such s o u r c e s can be activated by h y d r o s t a t i c p r e s s u r e , 8 cold work, 7'9 o r by r a p i d cooling 9 to produce h e l i c a l d i s l o c a t i o n s , d i s l o c a t i o n loops, or c o m p l e x d i s l o c a t i o n t a n g l e s . In this p a p e r , we d e s c r i b e s o m e s t u d i e s of d i s l o c a tion p r o d u c t i o n (including loops) by rapid heating of i r o n c o n t a i n i n g m e t a s t a b l e c a r b i d e p a r t i c l e s . We b e l i e v e this to be the f i r s t r e p o r t e d i n s t a n c e of the f o r m a t i o n of w e l l - d e f i n e d loops d u r i n g an u p - q u e n c h t r e a t m e n t .
The r a t e of r a p i d heating was v a r i e d by u s i n g t h r e e d i f f e r e n t t e c h n i q u e s . The s l o w e s t r a t e was attained by u s i n g h e l i u m as an i n t e r m e d i a t e heat t r a n s f e r m e d i u m . This was done by i n s e r t i n g the s t r i p s a m p l e s into a 12 m m ID s t a i n l e s s s t e e l tube so that only the edges of the s t r i p s could make m e t a l - t o - m e t a l c o n t a c t with the tube. The tube was evacuated, r e f i l l e d with 200 t o r r of helium, then plunged into a m o l t e n lead bath. The heating was t e r m i n a t e d by r e m o v i n g the tube r a p i d l y and quenching in chilled w a t e r . A m o r e r a p i d heating r a t e was obtained by i m m e r s i n g s p e c i m e n s , e i t h e r b a r e or o i l coated, into m o l t e n lead. F i n a l l y , the m o s t rapid heating was done by exposing one s u r f a c e of a s p e c i m e n to a l a s e r b e a m . The m i l l i v o l t - t i m e r e c o r d from a c h r o m e l - a l u m e l t h e r m o c o u p l e attached to the r e v e r s e side of the s p e c i m e n was photographed on an e x t e r n a l l y t r i g gered o s c i l l o s c o p e . After r a p i d heating, the s p e c i m e n s w e r e e l e c t r o l y t i cally thinned at 20~ in ~ 30 m i n
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