Low cycle fatigue behavior of inconel 718 at 298 K and 823 K
- PDF / 4,167,187 Bytes
- 11 Pages / 612 x 792 pts (letter) Page_size
- 45 Downloads / 193 Views
INCONEL
718 i s a high s t r e n g t h w r o u g h t n i c k e l b a s e a l l o y which was d e v e l o p e d f o r u s e at t e m p e r a t u r e s up to about 920 K. T h i s a l l o y is u s e d e x t e n s i v e l y in the gas t u r b i n e i n d u s t r y f o r a c e r t a i n n u m b e r of a p p l i c a t i o n s s u c h a s the f a b r i c a t i o n of d i s k s w h e r e the r e s i s t a n c e to low c y c l e fatigue (LCF) at e l e v a t e d t e m p e r a t u r e s (~-823 K) i s an i m p o r t a n t p r o p erty. Since the e a r l y w o r k by E i s e l s t e i n , 1 the p h y s i c a l m e t a l l u r g y of I n c o n e l 718 h a s b e e n f i r m l y e s t a b l i s h e d . The p r i m a r y s t r e n g t h e n i n g p h a s e has b e e n i d e n t i f i e d a s 7" (bct DO22 s t r u c t u r e ) . 2 The 7 " precipitates appear as coherent disc-shaped partic l e s and with the following o r i e n t a t i o n r e l a t i o n s h i p s : (001)7"//{001}and [20017"//(100). Moreover this a l l o y c o n t a i n s a l s o a s m a l l quantity of s p h e r i c a l 7 ' (L12 s t r u c t u r e ) p a r t i c l e s . Upon p r o l o n g e d a g i n g the 7" p h a s e i s r e p l a c e d by the e q u i l i b r i u m o r t h o r h o m b i c /3NiaNb p h a s e . In a N i - F e - C r - N b a l l o y , K i r m a n and W a r r i n g t o n showed that the f o r m a t i o n of the s t a b l e / 3 p h a s e is a c c e l e r a t e d by a p r e d e f o r m a t i o n b e f o r e aging. 3 T h i s was u s e d to r e v e a l the p l a s t i c zone s u r r o u n d i n g f a t i g u e c r a c k s in A l l o y 718. 4 Only a few s t u d i e s have b e e n p u b l i s h e d c o n c e r n hag the L C F p r o p e r t i e s of I n c o n e l 718 while the L C F c h a r a c t e r i s t i c s of o t h e r n i c k e l - b a s e a l l o y s s u c h a s U d i m e t 700 (Ref. 5) and M a r M200 (Refs. 6, 7) a r e b e t t e r d o c u m e n t e d . The g e n e r a l b e h a v i o r of n i c k e l b a s e a l l o y s h a s been r e v i e w e d by G e l l et al. 8 M o r e r e c e n t l y , M e r r i c k i n v e s t i g a t e d the L C F of t h r e e wrought n i c k e l b a s e a l l o y s : W a s p a l o y , A l l o y 901 and A l l o y 718. 9 T h i s a u t h o r h a s d e m o n s t r a t e d that f o r D. FOURNIER, formerly with Centre des Materiaux, is now with Turbomeca Company, Bordes, 64320 Pizanos and A. PINEAU is with the Centre des Matenaux de l'Ecole des Mines de Paris, BP. 87, 91003 Evry Cedex. Manuscript submitted October 7, 1976. METALLURGICAL TRANSACTIONS A
a given t o t a l s t r a i n r a n g e an i n c r e a s e in t e m p e r a t u r e f r o m 298 to 811 K l e a d s to a s u b s t a n t i a l r e d u c t i o n in fatigue l i f e . In this study, it was shown that Inconel 718 e x p e r i e n c e s a s h o r t p e r i o d of v e r y l i t t l e h a r d e n i n g followed by softening at 298 K. At 811 K no fatigue h a r d e n i n g was o b s e r v e d . M e r r i c k gave s o m e e v i d e n c e to r e l a t e the o b s e r v e d f a t i
Data Loading...
