The oxidation resistance of fine-grained sputter-deposited 304 stainless steel
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T h e a i r o x i d a t i o n of f r e e s t a n d i n g 0.1 c m t h i c k s p u t t e r - d e p o s i t e d and w r o u g h t 304 s t a i n l e s s s t e e l s p e c i m e n s was s t u d i e d and the long t e r m o x i d a t i o n weight g a i n s of the s p u t t e r d e p o s i t e d m a t e r i a l w e r e m u c h l e s s t h a n weight g a i n s f o r the w r o u g h t m a t e r i a l at 800, 900, and 1000~ T h e a m o u n t of s c a l i n g w a s a l s o m u c h l e s s on t h e s p u t t e r e d m a t e r i a l a n d a thin, a d h e r e n t oxide f o r m e d . T h e oxide on the s p u t t e r e d m a t e r i a l was m o r e unif o r m in c o m p o s i t i o n and was h i g h e r in c h r o m i u m and m a n g a n e s e c o m p a r e d to oxide on w r o u g h t s t a i n l e s s and e v e n t u a l l y f o r m e d MnCr204 a f t e r long p e r i o d s of e x p o s u r e . No s t r a t i f i e d oxide l a y e r s , a s t y p i c a l l y o b s e r v e d in wrought s t a i n l e s s s t e e l , f o r m e d on the f i n e - g r a i n e d s p u t t e r e d m a t e r i a l . T h e i m p r o v e d s c a l i n g r e s i s t a n c e of the s p u t t e r - d e p o s i t e d s t e e l was a t t r i b u t e d to a c o m b i n a t i o n of g r a i n b o u n d a r y e n h a n c e m e n t of c h r o m i u m diffusion, r e d u c e d s t r e s s e s in the oxide and m e c h a n i c a l k e y i n g of the o x i d e to c l o s e l y s p a c e d g r a i n b o u n d a r i e s . T h e s t a b i l i t y of g r a i n s i z e f o r the s p u t t e r e d m a t e r i a l ( g r a i n s i z e -< 6 /~m) a l s o c o n t r i b u t e d to the b e t t e r oxide a d h e r e n c e .
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f i n e - g r a i n e d s p u t t e r - d e p o s i t e d 304 s t a i n l e s s s t e e l f o r u n u s u a l p r o p e r t i e s , l i t t l e s c a l i n g was o b s e r v e d d u r i n g high t e m p e r a t u r e oxidation in a i r , F i g . 1. To d e t e r m i n e the m e c h a n i s m f o r the i m p r o v e d oxidation r e s i s t a n c e , s p e c i m e n s of both s p u t t e r - d e p o s i t e d and wrought 304 s t a i n l e s s w e r e o x i d i z e d at 800, 900 and 1000~ for p e r i o d s a s long a s 1000 h and weight g a i n s w e r e continuously m o n i t o r e d . T h e c o m p o s i t i o n s n e a r and in the v a r i o u s o x i d e s w e r e e x a m i n e d and the m o r p h o l o g y of o x i d e s w e r e c o m p a r e d to a s s e s s c h e m i c a l and s t r e s s e f f e c t s r e s p o n s i b l e for the i m p r o v e m e n t in o x i d a t i o n r e s i s t a n c e . The o x i d a t i o n of F e - C r - N i a l l o y s i n v o l v e s the a p p e a r a n c e of s e v e r a l o x i d e s i n c l u d i n g s p i n e l s , r h o m b o h e d r a l p h a s e s and s o l u t i o n s of t h e s e p h a s e s and often the s u r p r i s i n g a p p e a r a n c e of l a r g e a m o u n t s of oxide high in c o n c e n t r a t i o n of m i n o r a l l o y c o n s t i t u e n t s such a s m a n g a n e s e . The f o r m a
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