Deformation characteristics of Ti-6Al-4V alloy under isothermal forging conditions
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J. E. COYNE
An i n v e s t i g a t i o n was u n d e r t a k e n to d e t e r m i n e the i n f l u e n c e of forge t e m p e r a t u r e , r a m r a t e , and s t a r t i n g m i c r o s t r u c t u r e on the d e f o r m a t i o n c h a r a c t e r i s t i c s of i s o t h e r m a l l y f o r g e d Ti-6A1-4V alloy. Both y i e l d i n g and f i n i s h forge p r e s s u r e s w e r e m e a s u r e d i n the p r a c t i c a l r a n g e of forge t e m p e r a t u r e s and r a m r a t e s . With the a b s e n c e of d i e - c h i l l i n g , the r e s u l t s obtained can be q u a n t i t a t i v e l y r e l a t e d to the hot d e f o r m a t i o n p r o p e r t i e s . The y i e l d i n g and f i n i s h forge p r e s s u r e s and the s t r e s s - s t r a i n r e l a t i o n s h i p a r e s t r o n g l y dependent on forge t e m p e r a t u r e , r a m r a t e , and i n i t i a l m i c r o s t r u c t u r e . Although the forge p r e s s u r e s do not v a r y s i g n i f i c a n t l y with s t r a i n , an a p p a r e n t y i e l d - d r o p was o b s e r v e d , p a r t i c u l a r l y in the/3 p r e f o r m s . On the b a s i s of the above e x p e r i m e n t a l f i n d i n g s and the a c t i v a t i o n a n a l y s i s , the r a t e - c o n t r o l l i n g d e f o r m a t i o n p r o c e s s u n d e r i s o t h e r m a l f o r g i n g s is d i s c u s s e d with r e s p e c t to the d y n a m i c s o f t e n i n g . A d d i t i o n a l o b s e r v a t i o n was made on d y n a m i c r e c r y s t a l l i z a t i o n in the t e m p e r a t u r e r a n g e of 1500°F (1089 K) to 1650°F (1172 K). S t r u c t u r a l f e a t u r e s and t e n s i l e p r o p e r t i e s of i s o t h e r m a l l y forged m a t e r i a l a r e also p r e sented.
IN r e c e n t
y e a r s , one of the m o s t i m p o r t a n t a c h i e v e m e n t s for the f o r g i n g technology has b e e n the d e v e l o p m e n t of i s o t h e r m a l h o t - d i e t e c h n i q u e s for p r o d u c i n g net or n e a r - n e t f o r g i n g s . 1-4 The m a j o r c o n t r i b u t i o n of the i s o t h e r m a l f o r g i n g is to r e d u c e or to e l i m i n a t e the influence of die c h i l l i n g and m a t e r i a l s s t r a i n h a r d e n i n g . As a c o n s e q u e n c e , b e t t e r u t i l i z a t i o n of m a t e r i a l , s u b s t a n t i a l r e d u c t i o n of m a c h i n i n g cost, and r e d u c e d n u m b e r of f o r g i n g o p e r a t i o n s could be achieved. In the case of t i t a n i u m alloy f o r g i n g s , c o n s i d e r a b l e effort has b e e n d i r e c t e d at the p r a c t i c a l methods of i s o t h e r m a l forging, 1-4 but little c o n c e r n has b e e n made on the n a t u r e of the d e f o r m a t i o n p r o c e s s u n d e r i s o t h e r m a l conditions. T h i s u n d e r s t a n d i n g i s of t e c h n o l o g i c a l i m p o r t a n c e b e c a u s e the m a n u f a c t u r i n g capab i l i t y for i s o t h e r m a l p r o c e s s i n g r e q u i r e s the knowledge o
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