Analysis of primary creep of molybdenum at high temperatures
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Analysis of Primary Creep of Molybdenum at High Temperatures R . H . ERICKSEN AND G. J. JONES The high t e m p e r a t u r e c r e e p b e h a v i o r of p o l y c r y s t a l l i n e m o l y b d e n u m was i n v e s t i g a t e d at 1720~ u s i n g c o n s t a n t s t r e s s t e s t s in an u l t r a - h i g h v a c u u m e n v i r o n m e n t . The s t r a i n d e p e n d e n c e of the d i s l o c a t i o n s u b s t r u c t u r e was e x a m i n e d u s i n g etch pit t e c h n i q u e s and t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y . S u b b o u n d a r i e s w e r e f o r m e d e a r l y in the t r a n s i e n t region of the c r e e p c u r v e , and the d e t a i l s of t h i s s u b s t r u c t u r e d e v e l o p m e n t a r e p r e s e n t e d . G r a i n growth o c c u r r e d d u r i n g t e s t i n g , and this p h e n o m e n a is d i s c u s s e d in t e r m s of d e v i a t i o n s f r o m p a r a b o l i c t i m e law b e h a v i o r . V a r i o u s t i m e laws w e r e applied to the data and the Li equation was found to give the b e s t fit. T h i s equation was s u b s e q u e n t l y used to evaluate a model for d i s l o c a t i o n r e m o b i l i z a t i o n . A LTHOUGH c r e e p has been i n v e s t i g a t e d for a n u m b e r of y e a r s , m a n y d e t a i l s of the c r e e p p r o c e s s have not b e e n r e s o l v e d , p a r t i c u l a r l y those c o n c e r n i n g t r a n s i e n t b e h a v i o r . S u b s t r u c t u r a l d e t a i l s m u s t be involved in any model for p r i m a r y c r e e p ; and, as such, it is i m p o r t a n t that the r e l a t i o n s h i p between the shape of the c r e e p c u r v e a n d the r e s u l t i n g m i c r o s t r u c t u r a l c h a n g e s b e u n d e r s t o o d . S e v e r a l efforts have been m a d e to obtain a c o r r e l a t i o n , and m o s t of the p e r t i n e n t i n f o r m a t i o n is found in the r e v i e w s by Garofalo ~ and B i r d et a l l R e cently, C l a u e r et al., 3'4 have i n v e s t i g a t e d the c r e e p b e h a v i o r and d i s l o c a t i o n s u b s t r u c t u r e of m o l y b d e n u m s i n g l e c r y s t a l s . The d i s l o c a t i o n s u b s t r u c t u r e which f o r m s in p o l y c r y s t a l l i n e m a t e r i a l s is influenced by the n u m b e r of slip s y s t e m s p r o d u c e d by complex i n t e r n a l s t r e s s fields and, a s such, m a y differ f r o m the s i n g l e c r y s t a l r e s u l t s . T h e r e f o r e , the p r e s e n t study was u n d e r t a k e n a s a logical e x t e n s i o n of the s i n g l e c r y s t a l work. M e t a l l o g r a p h i c e x a m i n a t i o n of s t r u c t u r e s f o r m e d d u r i n g c r e e p was m a d e u s i n g optical and t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y , and m e c h a n i c a l b e h a v i o r was c h a r a c t e r i z e d by m e a n s of s e v e r a l of the m o r e c o m m o n l y used t i m e laws. PROCEDURE C r e e p s p e c i m e n s having a gage d i a m e t e
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