Anisotropic ductility of a superplastic aluminum bronze
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Anisotropic Ductility of a Superplastic Aluminum Bronze G. L. D U N L O P ,
J.D. REID, A N D
D. M. R. T A P L I N
T H E p u r p o s e of t h i s c o m m u n i c a t i o n i s to p r e s e n t c e r t a i n u n u s u a l e x p e r i m e n t a l r e s u l t s o b t a i n e d in a s t u d y of of t h e h i g h t e m p e r a t u r e s u p e r p l a s t i c b e h a v i o r z'2 of a m i c r o d u p l e x a l u m i n u m b r o n z e . E l o n g a t i o n to f r a c t u r e and strain-rate sensitivity exponent, m,' were determ i n e d a s a f u n c t i o n of t h e a n g l e of t h e t e n s i l e a x i s to t h e r o l l i n g d i r e c t i o n in s h e e t s p e c i m e n s . T h e a l l o y (CDA 619) h a s a n o m i n a l c o m p o s i t i o n of C u - 9 . 5 p c t A14 pct Fe and was developed by Olin Corporation as a high strength oxidation resistant material. ~ Sheet mat e r i a l (1 m m t h i c k ) w a s s u p p l i e d a n d t e n s i l e s p e c i m e n s of g a g e l e n g t h 13.3 m m a n d 4 . 5 m m w i d t h w e r e c u t w i t h t e n s i l e a x e s a t 0, 4 5 , a n d 90 d e g to t h e r o l l i n g d i rection. Tensile testing was carried out on Instron m a c h i n e s i n a i r a t 800~ at constant engineering s t r a i n - r a t e s of 2.3 x 10 -2 m i n -1, 7.8 x 10 -2 m i n - t a n d 1.6 m i n - z V a l u e s of m w e r e d e t e r m i n e d b y t h e c h a n g e rate methodJ Prior to testing the specimens were ann e a l e d f o r 30 m i n a t 800~ i n t h e t e s t i n g a p p a r a t u s . A f t e r t h i s t r e a t m e n t o p t i c a l m e t a l l o g r a p h y of q u e n c h e d s p e c i m e n s s h o w e d a f i n e d u p l e x m i c r o s t r u c t u r e of (fcc) a n d / 3 ( b c c ) p h a s e s w i t h a r a n d o m a r r a y of 5 i r o n rich particles through both phases, Fig. l(a). The a v e r a g e s i z e of u a n d ~ p h a s e s w a s a p p r o x i m a t e l y 1 0 p m . E l e c t r o n m e t a l l o g r a p h y i n d i c a t e d (by t h e s e p a r a t i o n of p a r t i a l d i s l o c a t i o n s ) a low s t a c k i n g f a u l t e n e r g y f o r t h e a p h a s e a n d a v e r y f i n e d i s p e r s i o n of c o h e r e n t i r o n - r i c h p r e c i p i t a t e p a r t i c l e s i n t h e ;3 p h a s e , Fig. l(b). The large 6 iron-rich particles were obs e r v e d to " p i n " g r a i n b o u n d a r i e s , t h u s r e s t r i c t i n g g r a i n g r o w t h . A s i m i l a r c o m b i n a t i o n of p h a s e s in a c o a r s e m i c r o s t r u c t u r e w o u l d b e e x p e c t e d to p r o v i d e good creep strength but with the present fine grain s i z e a m a x i m u m e n g i n e e r i n g s t r e s s a s low a s 0 . 5 M N / m 2 (75 p s i ) w i t h a t o t a l e l o n g a t i o n e x c e e d i n g 700 pct may be obtained under optimum superplastic s t r a i n r a t e c o n d i t i o n s a t 800~ This alloy thus has potential in high temperature "creep-forming" appliG. L. DUNLOP, J. D. REID, and D. M. R. TAPLIN are Research Assistant, Undergraduate, and Associate Professor
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