The effect of thermal cycling on the structure and properties of a Co, Cr, Ni-TaC directionally solidified eutectic allo

  • PDF / 2,224,298 Bytes
  • 6 Pages / 612 x 783.28 pts Page_size
  • 22 Downloads / 189 Views

DOWNLOAD

REPORT


T H E s u b s t a n t i a l i n c r e a s e in the efficiency of a gas turbine engine with i n c r e a s e d turbine inlet t e m p e r a ture has led to the c o n s i d e r a t i o n of composite m a t e r i a l s f o r use as turbine blade a l l o y s . The excellent high t e m p e r a t u r e strength and room t e m p e r a t u r e ductility1 of a d i r e c t i o n a l l y solidified eutectic (DSE) that p r o v i d e s a r e f r a c t o r y metal monocarbide fiber and a s u p e r a l l o y m a t r i x have made these m a t e r i a l s a t t r a c t i v e for engine applications. A cobalt alloy m a t r i x r e i n f o r c e d by TaC f i b e r s has the best p r o p e r t i e s above 1100~ of the r e f r a c t o r y m e t a l monocarbide s y s t e m s r e p o r t e d 1-5 and app e a r s to be among the most p r o m i s i n g for future f i r s t stage turbine b l a d e s . The l a r g e difference between the t h e r m a l expansion coefficients of the cobalt alloy m a t r i x (-18 x 10-6/~ 6 and the TaC phase (~6 x 10-e/~ has caused some concern for the s t a b i l i t y of these alloys under conditions of t h e r m a l fatiguefl '9 Breinan s has r e p o r t e d mechanical and m i c r o s t r u c t u r a l d e g r a d a tion in the s y s t e m Co, C r , Ni-TaC when cycled between 400 and 1120~ Bibring 1~ r e p o r t s the s a t i s f a c t o r y p e r f o r m a n c e of Co, C r , Ni-TaC and Ni, C r - T a C DSE a l l o y s cycled between 250 and 1070~ T e s t s by Benz 1. have shown that the Co, C r - T a C s y s t e m , which is unstabilized with r e s p e c t to the HCP ~ F C C t r a n s f o r m a t i o n of cobalt, s u f f e r s a degradation of elevated t e m p e r a t u r e m e c h a n i c a l p r o p e r t i e s a f t e r cycling b e tween 95 and 1093~ On the other hand, the alloy CoSOB3W, s t a b i l i z e d by the addition of g.5 pet nickel, actually showed an i n i t i a l i m p r o v e m e n t in s t r e s s rupture p r o p e r t i e s when cycled between 95 and 1093~ This investigation was d i r e c t e d at: a) studying the F. M. DUNLEVEY, formerly Graduate Student, Case Western Reserve University,is now with Gould Laboratories,Cleveland,Ohio. J. F. WALLACEis Professor of Metallurgy,Case Western ReserveUniversity, Cleveland,Ohio 44106. Manuscript submitted July 2, 1973. METALLURGICALTRANSACTIONS

effects of t h e r m a l fatigue on TaC r e i n f o r c e d DSE cobalt b a s e alloys in t e r m s of m i c r o s t r u c t u r a l changes and a l t e r a t i o n of m e c h a n i c a l p r o p e r t i e s , b) evaluating the suitability of TaC r e i n f o r c e d s u p e r a l l o y m a t r i x DSE alloys for use in gas turbine engines up to 1200~ EXPER/MENTAL PROCEDURE AND MATERIALS As an initial step, p r i o r to d i r e c t i o n a l solidification, the e l e m e n t a l m a t e r i a l s (all at l e a s t 99.5 pet pure) w e r e melted and c a s t into ingots that w e r e homogeneous and had a'convenient shape for the d i r e c t i o n a l solidification a p p a r a t u s . I n i t i a l melting was condu

Data Loading...