Electron microscopic studies of martensitic transformations in iron alloys and steels
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IN o r d e r
to know the c r y s t a l l o g r a p h i c m e c h a n i s m of t r a n s f o r m a t i o n s , it i s n e c e s s a r y to c l a r i f y the s u b s t r u c t u r e s in the p r o d u c t a n d m a t r i x p h a s e s . H o w e v e r , the s u b s t r u c t u r e s a r e g e n e r a l l y so fine that they a r e not d e t e c t a b l e by c o n v e n t i o n a l optical m i c r o s c o p y . Thus, the e l e c t r o n m i c r o s c o p e has come into the l i m e light a s a r e s e a r c h tool in the field of phase t r a n s f o r m a t i o n a s well a s m a n y o t h e r f i e l d s . T h e etched a n d / o r u n e t c h e d s u r f a c e s of p e a r l i t e , b a i n i t e , and m a r t e n s i t e have b e e n o b s e r v e d f i r s t by the r e p l i c a t e c h n i q u e . In the 1950's, a new t e c h n i q u e was e s t a b l i s h e d w h e r e b y thin foils w e r e p r e p a r e d f r o m bulk s p e c i m e n s and exa m i n e d d i r e c t l y by t r a n s m i s s i o n in the e l e c t r o n m i c r o scope. The t r a n s m i s s i o n method e n a b l e s the m e r i t s of high r e s o l v i n g power and s e l e c t e d - a r e a e l e c t r o n d i f f r a c t i o n in the m o d e r n e l e c t r o n m i c r o s c o p e to be fully u t i l i z e d . It a l s o m a k e s p o s s i b l e the o b s e r v a t i o n of l a t t i c e d e f e c t s such a s d i s l o c a t i o n l i n e s and s t a c k i n g f a u l t s . F u r t h e r , the o b s e r v a t i o n s r e p r e s e n t a t h r e e d i m e n s i o n a l p i c t u r e of the m i c r o s t r u c t u r e . That i s , the t r a n s m i s s i o n method has m a n y a d v a n t a g e s o v e r the r e p l i c a method. T h e r e f o r e , a l m o s t all r e c e n t e l e c t r o n m i c r o g r a p h s a r e c a r r i e d out by the t r a n s m i s s i o n method. The p h e n o m e n o l o g i c a l c r y s t a l l o g r a p h i c t h e o r i e s of m a r t e n s i t e f o r m a t i o n l'z i n t r o d u c e d in the 1950's r e q u i r e t h r e e o p e r a t o r s : the Bain d i s t o r t i o n for the n e c e s s a r y l a t t i c e change, a l a t t i c e i n v a r l a n t i n h o m o g e n e o u s s h e a r which p r o v i d e s a n u n d i s t o r t e d habit plane, and a r o t a t i o n to i n s u r e that the u n d i s t o r t e d habit p l a n e i s a l s o u n r o t a t e d . The r e s u l t a n t of t h e s e t h r e e o p e r a t i o n s m u s t be e q u i v a l e n t to the total shape d e f o r m a t i o n a n d thus the o b s e r v e d s u r f a c e d i s t o r t i o n . It should be noted that the t h e o r y Js p h e n o m e n o l o g i c a l and does not d e s c r i b e how the pher, o m e n a c o r r e s p o n d i n g to the o p e r a t i o n s a c t u a l l y o c c u r . However, the t h e o r y i s not completely divorced from physical reality because the i n h o m o g e n e o u s s h e a r s r e q u i r e d in the t h e o r y have K. SHIMIZUis associated with the Institute of Scientific and Industrial Researc
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