Dynamic elastic moduli of the titanium aluminides
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E N G I N E E R I N G a p p l i c a t i o n s of the t i t a n i u m a l u m i n ides, Ti3A1 and TiA1, r e q u i r e a knowledge of how the e l a s t i c m o d u l i (namely Young's m o d u l u s and the s h e a r modulus) change with i n c r e a s i n g t e m p e r a t u r e . A d y n a m i c e l a s t i c t e s t technique is e s p e c i a l l y s u i t e d t o d e t e r m i n e t h e s e r e l a t i o n s h i p s b e c a u s e , being a nond e s t r u c t i v e t e s t method, r e l a t i v e l y few s p e c i m e n s need be m a n u f a c t u r e d . Also, the u s u a l e r r o r s i n h e r e n t in a m e c h a n i c a l m o d u l u s t e s t at e l e v a t e d t e m p e r a t u r e s c a n be e l i m i n a t e d , i.e., r e l a t i v e l a c k of s e n s i t i v i t y of the s t r a i n m e a s u r i n g s y s t e m and the effect of i n c r e a s i n g p r e - y i e l d m i c r o s t r a i n at the h i g h e r t e m p e r a t u r e s . 1 T h e o b j e c t of t h i s p a p e r i s to r e p o r t the e l a s t i c m o d u l i of TiA1, Ti3A1, and Ti3AI with 10 wt p c t Cb (Nb) o v e r a t e m p e r a t u r e r a n g e of 25 to 940~ The m o d u l i w e r e d e t e r m i n e d by m e a s u r i n g the sonic r e s o n a n t f r e q u e n c y for different vibrational modes. E x p e r i m e n t a l P r o c e d u r e . B a r s of the t i t a n i u m a l u m i n i d e s w e r e p r e p a r e d by canning p r e a l l o y e d p o w d e r in a t i t a n i u m b i l l e t , extruding, and then decanning. The m a t e r i a l w a s 100 pct d e n s e and w a s r e l a t i v e l y f r e e of i n t e r n a l oxide p a r t i c l e s . The c o m p l e t e p r o c e s s i n g s e q u e n c e i s the s a m e a s that p r e v i o u s l y r e p o r t e d . 1 C h e m i c a l c o m p o s i t i o n s a r e shown in T a b l e I and e x t r u s i o n p r o c e s s i n g p a r a m e t e r s a r e shown in T a b l e II. The r o d s u s e d in t h i s study w e r e r i g h t c i r c u l a r c y l i n d e r s , r a n g i n g in length f r o m 8.5 to 13.0 c m and in d i a m e t e r f r o m 8.0 to 11.0 m m . M e a s u r e m e n t s w e r e c o n d u c t e d on an E l a s t o m a t F M - 5 0 0 sonic t e s t e r , and a s s o c i a t e d a p p a r a t u s . The r o d s w e r e s u p p o r t e d in the t w o - p i e c e r e s i s t a n c e - w o u n d f u r n a c e on p l a t i n u m w i r e s at f u n d a m e n t a l t r a n s v e r s e f r e q u e n c y node points. P i e z o e l e c t r i c t r a n s d u c e r s w e r e u s e d to e x c i t e the r o d s and to p i c k - u p the r e s u l t a n t e l a s t i c wave e n e r g y . N i c h r o m e w i r e (0.10 m m d i a m ) w a s spot w e l d e d to the b a r and c o n n e c t e d to the t r a n s d u c e r c r y s t a l by m e a n s of n i c k e l e x t e n s i o n t u b e s which p a s s e d t h r o u g h the f u r n a c e lining. The w i r e w a s a t t a c h e d to the r o d at one of two l o c a t i o n s : a) the end of the rod, a p p r o x i m a t e l y 1 ram f r o m the c i r c u m f e
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