Thermomechanical Manipulation of Precipitate Shape in a Titanium-Base Alloy
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Thermomechanical Manipulation of Precipitate Shape in a Titanium-Base Alloy J. K. TIEN, J. C. CHESNUTT, AND D. E. PEACOCK Fig. 10--Radialcracks on the equatorial plane of an iron specimen.
in s i n t e r e d n i c k e l s a m p l e s . A l e s s p r o n o u n c e d p l a t e a u in ez vs e~ i s noted. A t a hoop s t r a i n of 0.12, the r a d i a l s t r a i n r e v e r s e s s l o p e and d r o p s with a s l o p e of a p p r o x i m a t e l y - 1 . At a hoop s t r a i n of 0.15, the r a d i a l s t r a i n , Cr, or (-~z - co) r e a c h e s a p l a t e a u , and the a x i a l s t r a i n i n c r e a s e s again. At a hoop s t r a i n of 0.17 a s e c o n d p l a t e a u in a x i a l s t r a i n i s a p p r o a c h e d and this r a d i a l s t r a i n b e h a v i o r i s again r e p e a t e d . At f r a c t u r e , n i c k e l s a m p l e s r e v e a l s e v e r a l l a r g e v e r t i c a l c r a c k s which a p p e a r along with f i n e r h o r i z o n t a l c i r c u m f e r e n t i a l c r a c k s , Fig~ 6. The h o r i z o n t a l and v e r t i c a l c r a c k s a p p e a r to i n i t i a t e s i m u l t a n e o u s l y with the v e r t i c a l c r a c k s p r o p a g a t i n g and e n l a r g i n g at a f a s t e r r a t e . A s e c o n d type of f r a c t u r e , as s e e n in i r o n c o m p a c t s , F i g . 7, r e v e a l s c r a c k s p r o p a g a t i n g at i n c l i n e d a n g l e s (not n e c e s s a r i l y at 45 ~) to the v e r t i c a l with only a s m a l l p o r t i o n of the c r a c k p a r a l l e l to the v e r t i c a l d i r e c t i o n . S e v e r a l t r a n s v e r s e s e c t i o n s at the e q u a t o r i a l p l a n e w e r e cut and m e t a l l o g r a p h i c a l l y e x a m i n e d . Once a c r a c k has i n i t i a t e d , r a d i a l p r o p a g a t i o n in n i c k e l c o m p a c t s g e n e r a l l y o c c u r s along g r a i n b o u n d a r i e s , linking l a r g e p o r e s , F i g . 8. In i r o n c o m p a c t s , p r o p a g a t i o n is a l s o r a d i a l , however the mode m a y be t r a n s g r a n u l a r , depending on the p o r e d i s t r i bution, F i g s . 9 and 10. C o n s e q u e n t l y , the m e c h a n i s m of c r a c k p r o p a g a t i o n is dependent on the p o r o s i t y , as d e t e r m i n e d by the a s - r e c e i v e d p o w d e r , d e n s i t y and s i n t e r i n g p a r a m e t e r s . C o n c l u s i o n . S t r a i n i n s t a b i l i t i e s c h a r a c t e r i s t i c of fully dense materials during compressive upsetting were a l s o o b s e r v e d in s i n t e r e d c o m p a c t s . Although the p e r t u r b a t i o n is not a s p r o n o u n c e d , it is s u g g e s t e d that such a s t r a i n a n a l y s i s can p r o v i d e an i n s i g h t for fracture criteria for compressively upset sintered p o w d e r c o m p a c t s a s a p p l i c a b l e to powder p r e f o r m forgings. The a u t h o r s acknowledge p r o g r a m s u p p o r t under P r o j e c t THEMIS, P o w d e r M e t a l l u r g y P r o d u c t i o n of S t r u
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