The low cycle fatigue of three wrought nickel-base alloys
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r e c e n t y e a r s the low c y c l e fatigue (LCF) b e h a v i o r of m a t e r i a l s h a s r e c e i v e d a g r e a t d e a l of a t t e n t i o n . T h e r e i s c o n s i d e r a b l e i n t e r e s t in the L C F of n i c k e l b a s e s u p e r a l l o y s not only f r o m a f u n d a m e n t a l point of view, but a l s o the p r a c t i c a l one. It i s r e c o g n i z e d that in m a n y c a s e s the L C F p e r f o r m a n c e of n i c k e l - b a s e a l l o y s can be a l i m i t i n g f a c t o r in the s e l e c t i o n of an a l l o y in t u r b i n e e n g i n e s . A n u m b e r of p a p e r s have b e e n w r i t t e n c o n c e r n i n g the L C F of n i c k e l - b a s e a l l o y s a t both a m b i e n t and e l e v a t e d t e m p e r a t u r e s . Notable a m o n g t h e s e i s the w o r k of W e l l s and Sullivan x'~'3'4 and Gell and L e v e r a n t 5 and L e v e r a n t and Gell. 8 T h e s e a u t h o r s have e x a m i n e d in d e t a i l the L C F c h a r a c t e r i s t i c s of U d i m e t A l l o y 700* *Trademarkof SpecialMetals,Inc. and a e a s t alloy Mar*-M200. The g e n e r a l b e h a v i o r *Trademarkof MartinMariettaCorporation of n i c k e l - b a s e The p r e s e n t on the L C F of v a t i o n s on the loy, a l l o y 901,
a l l o y s h a s b e e n r e v i e w e d b y Gell e t a l . ~ p a p e r a d d s to the b o d y of i n f o r m a t i o n n i c k e l - b a s e a l l o y s and d e a l s with o b s e r b e h a v i o r of t h r e e w r o u g h t a l l o y s : W a s p a a n d a l l o y 718.
to allow c y c l i n g at c o n s t a n t t o t a l s t r a i n . D i a m e t r a l strain measurements were determined using a jig simi l a r to that e m p l o y e d by Coffinfl E l e v a t e d t e m p e r a t u r e t e s t s w e r e p e r f o r m e d b y induction h e a t i n g . The t e m p e r a t u r e was c o n t r o l l e d b y m e a n s of a t h e r m o c o u p l e s p o t w e l d e d onto the s p e c i m e n one q u a r t e r of an inch a b o v e the m i n i m u m d i a m e t e r . Two o t h e r t h e r m o c o u p l e s f o r r e c o r d i n g the t e m p e r a t u r e w e r e s i m i l a r l y a t t a c h e d above and below the m i n i m u m d i a m e t e r of the s p e c i m e n a t the s a m e d i s t a n c e , one q u a r t e r of an inch. F a t i g u e t e s t s w e r e c o m m e n c e d when the t e m p e r a t u r e s m e a s u r e d b y the t h e r m o c o u p l e s w e r e within 5~ to 10~ of each o t h e r . M e t a l l o g r a p h i c p r e p a r a t i o n of l o n g i t u d i n a l l y s e c t i o n e d t e s t e d s p e c i m e n s was conducted using s t a n d a r d t e c h n i q u e s . An a q u e o u s 10 p e t I-IsPO4 s o l u t i o n u s e d e l e c t r o l y t i c a l l y o r a 92 p c t HC1- 5 p c t H~SO4-3 p c t HNOz c h e m i c a l etch was e m p l o y e d to r e v e a l s t r u c t u r a l d e t a i l b y o p t i c a l m i c r o s c o p y . Thin f o i l s p e c i m e n s f o r transmission electron microscopy were prepared from d i s c s , c
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