Creep fracture maps for 316 stainless steel
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1. INTRODUCTION P OLYCRYSTALLINE m a t e r i a l s may d e f o r m by s e v e r a l d i f f e r e n t m e c h a n i s m s when s u b j e c t e d to an applied s t r e s s , and it is c o n v e n i e n t to p r e s e n t these m e c h a n i s m s in the f o r m of a d e f o r m a t i o n m e c h a n i s m map. 1-3 S i m i l a r l y , p o l y c r y s t a l s may f r a c t u r e by s e v e r a l p o s s i b l e p r o c e s s e s , and the p r e c i s e mode of f r a c t u r e depends c r i t i c a l l y on the t e s t i n g conditions, such as s t r e s s and t e m p e r a t u r e , and on m a t e r i a l p a r a m e t e r s such as g r a i n size and the c o n c e n t r a t i o n of p r e c i p i t a t e s . W r a y 4 f i r s t suggested the p o s s i b i l i t y of d i s p l a y i n g f a i l u r e modes in the f o r m of a s c h e m a t i c d i a g r a m in s t r a i n r a t e - t e m p e r a t u r e space, and the concept was l a t e r i m p r o v e d and developed by Ashby and Raj 5 to give a f r a c t u r e map for c o p p e r . T h i s map plotted n o r m a l i z e d s t r e s s a g a i n s t homologous t e m p e r a t u r e , f r o m a b s o l u t e z e r o to the m e l t i n g point, and showed fields in s t r e s s - t e m p e r a t u r e space within which a p a r t i c u l a r f r a c t u r e m e c h a n i s m was d o m i n a n t . Ashby% 7 has d e s c r i b e d in d e t a i l the c o n s t r u c t i o n of f r a c t u r e maps of n o r m a l i z e d s t r e s s v s homologous t e m p e r a t u r e , and the r a p i d a c c e p t a n c e of this p r o c e d u r e is d e m o n s t r a t e d by the i n c l u s i o n of f r a c t u r e maps in s e v e r a l r e c e n t r e v i e w s 8-11 and the c o n s t r u c t i o n of maps of this type for a n u m b e r of d i f f e r e n t materials.12 iv The p r e s e n t work was u n d e r t a k e n with t h r e e specific objectives : 1) To develop a s i m p l i f i e d f o r m of f r a c t u r e map for the a n a l y s i s of c r e e p data at high homologous t e m p e r a t u r e s ; 2) T o use the t h e o r e t i c a l f r a c t u r e p r o c e s s e s to c o n s t r u c t c r e e p f r a c t u r e maps for 316 s t a i n l e s s steel; and 3) To make a d i r e c t c o m p a r i s o n b e t w e e n the p r e d i c t i o n s of the t h e o r e t i c a l maps and the b e s t a v a i l a b l e e x p e r i m e n t a l data. 2. FRACTURE MECHANISMS UNDER C R E E P CONDITIONS D u r i n g the high t e m p e r a t u r e c r e e p of a p o l y c r y s t a l l i n e m a t e r i a l , the s t e a d y - s t a t e c r e e p r a t e , ~, is DAVID A. MILLER, formerly Research Associate, Department of Materials Science, University of Southern California, is now Research Fellow, Department of MechanicalEngineering,University of Bristol, Bristol BS8 1TR, England. TERENCE G. LANGDONis Professor, Department of Materials Science, University of Southern California, Los Angeles,CA 90007. Manuscript submitted February 13, 1979. METALLURGICALTRANSACTIONSA
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