Deformation stress state effects on the recrystallization kinetics of molybdenum

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L.J.

EBERT

Studies of the recrystaUization characteristics of cold worked pure molybdenumindicated a dependence upon the mode of deformation and a definite dependence on the manner used to describe the deformation. On the basis of a constant amount of deformation strain, molybdenumdeformed in pure compression exhibited slower rates of recrystallization, higher activation energies and coarser grain sizes than that deformed in simple tension. Deformation by rolling produced recrystallization effects resembling those of compression, while straining by drawing resulted in rates similar to those of tension. THE microstructural and property changes that accompany the annealing of cold worked metals have been extensively investigated in the past for many metals and under various conditions.1-s'~~In general, these investigations have been concerned with the time and temperature dependentmechanisms which are classified in the usual three stages'--recovery, recrystallization, and grain growth. The variables recognized by most investigators to be associated with the annealing behavior of cold worked metals are: prior thermal treatments, heating and cooling rates, grain size, composition, and amount of deformation. In most investigations, these variables have been controlled independently,or assumed to be constant, and therefore were neglected in the final analysis. The mconsistency of values for such paranleters as activation energy (associated with recrystallization) and grain growth rates found in the literature can usually be attributed to variations in these variables among the particular investigations. The most extensively investigated variable associated with annealing cold worked metals has been the amount of deformation. Reviews of the literature by Beck, 2 Burke, a and Mehl 5 offer a comprehensive pres-. e n t a t i o n of t h e m a n y i n v e s t i g a t i o n s m a d e i n t o t h e e f f e c t s of t h i s v a r i a b l e on a n n e a l i n g p h e n o m e n o n . G e n e r a l l y , m o s t of t h e s e i n v e s t i g a t i o n s h a v e p l a c e d m i n o r e m p h a s i s on t h e t y p e o r m o d e of d e f o r m a t i o n , o r n e g l e c t e d it e n t i r e l y . Beck and Polanyt ~ obtained some evidence which m d i c a t e d t h a t t h e m e t h o d of d e f o r m i n g a s w e l l a s t h e m a g n i t u d e of t h e d e f o r m a t i o n i s i m p o r t a n t . W h e n b e n t s i n g l e c r y s t a l s of a l u m i n u m w e r e s t r a i g h t e n e d , a r e d u c t i o n in t h e a b i l i t y of t h e c r y s t a l s to r e c r y s t a l l i z e after reversed deformation was noted despite the press e n c e of a g r e a t e r t o t a l a m o u n t of s t r a i n . T h i s s u g g e s t s t h a t d i f f e r e n t m o d e s of d e f o r m a t i o n m a y a l s o affect annealing behavior. K a i s e r mad T a y l o r , z on t h e o t h e r h a n d , h a v e p r e s e n t e d e v i d e n c e t h a t t h e m e t h o d of d e f o r m i n g i s u n i m p o r t a n t , p r o v i d e d t h a t t h

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