Dynamic oxidation behavior of TD-NiCr alloy with different surface pretreatments
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BECAUSE
of its r e p o r t e d high s t r e n g t h and good s t a t i c oxidation r e s i s t a n c e at high t e m p e r a t u r e , x-'~ Ni-20 pct C r - 2 pct ThOe alloy, supplied u n d e r the trade n a m e of T D - N i C r , has been c o n s i d e r e d for use in a d v a n c e d jet e n g i n e s and as a p a r t of a t h e r m a l p r o t e c t i o n s y s t e m for the space s h u t t l e . The addition of s u b m i c r o n ThO2 p a r t i c l e s to the N i - C r alloy i n h i b i t s g r a i n growth and s t a b i l i z e s the s u b s t r u c t u r e of the alloy, t h e r e b y r e t a i n i n g high s t r e n g t h at e l e v a t e d t e m perature.~-4 The addition of t h o r i a p a r t i c l e s also i m p r o v e s s t a t i c oxidation r e s i s t a n c e by p r o m o t i n g the s e l e c t i v e oxidation of C r to f o r m p r o t e c t i v e Cr203, and by d e c r e a s i n g the growth r a t e of CrzO~. 6-9 Surface p r e p a r a t i o n has a s i g n i f i c a n t i n f l u e n c e on the o x i d a tion b e h a v i o r of the alloy. Surface g r i n d i n g e n h a n c e s the f o r m a t i o n of Cr203 w h e r e a s e l e c t r o p o l i s h i n g p r o m o t e s the f o r m a t i o n of e x t e r n a l NiO and i n n e r Cr203 subscale.8-~a U n d e r high t e m p e r a t u r e , high speed flowing gas c o n d i t i o n s , a s u b s t a n t i a l i n c r e a s e in the oxidation rate has been o b s e r v e d as c o m p a r e d with the r e s u l t s of static t e s t i n g . G i l b r e a t h ~3'~4 has e m p h a s i z e d the i m p o r t a n c e of atomic oxygen which e x i s t e d in the r e e n t r y e n v i r o n m e n t , and h a s d e m o n s t r a t e d the a c c e l e r a t e d d e g r a d a t i o n of the alloy in d i s s o c i a t e d oxygen. Lowell e t a l ~s has i n d i c a t e d that the l o s s rate of m a t e r i a l in a 1 - a t m o s p h e r e , M a c h - 1 t u r b i n e gas s t r e a m at 1200~ was a p p r o x i m a t e l y 100 t i m e s g r e a t e r than that of s t a t i c t e s t s . E n h a n c e d oxidation in a C. T. YOUNG is with Bendix Research Laboratories, The Bendix Corporation, Southfield, MI 48076. D. R. TENNEY is with NASALangley Research Center, Hampton, VA 23665. H. W. HERRING is with NASA-MarshallFlight Center, Huntsville, AL 35812. C.T. Young and H. W. Herring were formerly Research Fellow and Materials Engineer, respectively, NASA-LangleyResearch Center, Hampton, VA. D. R. Tenney was formerly Assistant Professor of Metallurgical Engineering, Division of MineralEngineering, Virginia Polytechnic Institute and State University, Blacksburg, VA. Manuscript submitted February 15, 1974. METALLURGICAL TRANSACTIONS A
M a c h - 1 b u r n e r gas s t r e a m at 1093~ was also obs e r v e d by J o h n s t o n e t a l . 16 C e n t o l e n z i e t a l ~7'~8 has r e p o r t e d i n c r e a s e d oxidation in a M a c h - 5 a r c - j e t gas s t r e a m , but no d e t a i l e d m e c h a n i s m has been given. The oxidation b e h a v i o r of T D - N i C r ( b e l t - s a n
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