Determination of the elastic moduli of a directionally solidified nickel-based TaC eutectic
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T H E R E is, at the p r e s e n t t i m e , c o n s i d e r a b l e i n t e r e s t and effort in developing n i c k e l b a s e d a l l o y s with m e c h a n i c a l p r o p e r t i e s that a r e s u i t a b l e for s e r v i c e a s a i r c r a f t t u r b i n e b l a d e s at t e m p e r a t u r e s exceeding 1000~ The a l l o y s that a r e of p r i m e i n t e r e s t a r e the d i r e c t i o n ally solidified fcc (y) m a t r i x with s u f f i c i e n t alloying additions to f o r m d i s p e r s e d second a n d / o r t h i r d phases.1 The p r e s e n t work is b a s e d on a study of the e l a s t i c p r o p e r t i e s of one of these alloys, with d i s p e r s e d y ' ( N i ~ l ) and with T a C f i b e r s f o r m e d as a e u t e c t i c phase d u r i n g d i r e c t i o n a l p l a n a r front s o l i d i f i c a t i o n . Although the p r e s e n c e of the p a r a l l e l f i b e r s was one of the p o i n t s of b a s i c i n t e r e s t in u n d e r t a k i n g this study, the p r o c e d u r e s and r e s u l t s a p p e a r to have g e n e r a l a p p l i c a t i o n to most of the d i r e c t i o n a l l y s o l i d i f i e d a l l o y s , including the s u p e r a l l o y s . The p r o c e d u r e for d e t e r m i n i n g the e l a s t i c p a r a m e t e r s is unique in that the d i r e c t i o n a l s o l i d i f i c a t i o n conditions e n a b l e the d e t e r m i n a t i o n of the single c r y s t a l e l a s t i c moduli Cll and C44 to be made d i r e c t l y f r o m high f r e q u e n c y wave v e locity m e a s u r e m e n t s on p o l y c r y s t a l l i n e s a m p l e s . The e l a s t i c modulus C12 is then e v a l u a t e d f r o m the m e a s u r e ment of Y o u n g ' s modulus along the cube axes u s i n g a low f r e q u e n c y r e s o n a n c e t e c h n i q u e . F r o m a knowledge of the t h r e e s t i f f n e s s moduli, Cij , and the p r e f e r r e d o r i e n t a t i o n of the r e l a t i v e l y l a r g e g r a i n e d s a m p l e s , one can e a s i l y c a l c u l a t e the e l a s t i c c o n s t a n t s of a p o l y c r y s t a l l i n e t u r b i n e blade in d i r e c t i o n s t r a n s v e r s e and 45 deg to the d i r e c t i o n a l l y s o l i d i f i e d a x i s . 2 T h i s p r o c e d u r e should find a p p l i c a t i o n to other t y p e s of m a t e r i a l s with f i b e r t e x t u r e s , p a r t i c u l a r l y those with f i b e r a x e s . The specific r e s u l t s given h e r e a r e a l s o of m o r e g e n e r a l i n t e r e s t in that the a n i s o t r o p y and the t e m p e r a t u r e d e p e n d e n c e of the e l a s t i c moduli in this alloy have v a l u e s v e r y close to those for the s a m e p a r a m e t e r s in p u r e p a r a m a g n e t i c n i c k e l . 3 It t h e r e f o r e a p p e a r s that the e l a s t i c p r o p e r t i e s of other y / y ' a l l o y s , with or without the T a C f i b e r s t r e n g t h e n i n g , will differ p r i m a r i l y in the magnitude of the i n d i v i d u a l e l a s t i
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