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M. J. KLEIN and A. G. METCALFE are Research Staff Specialist and Associate Director of Research, respectively, Solar Division of International Harvester Co., San Diego, Calif. 92138. Manuscript submitted February 15, 1973. METALLURGICAL TRANSACTIONS

of t i m e (~ 5 h). A d e t e r m i n a t i o n of c r e e p s t r e n g t h by c o n v e n t i o n a l methods would r e q u i r e that a s e p a r a t e s p e c i m e n be t e s t e d at each t e m p e r a t u r e . T h e r e f o r e , a l a r g e n u m b e r of s p e c i m e n s and s e p a r a t e t e s t s would be needed to d e t e r m i n e the c r e e p s t r e n g t h of a single alloy over a l a r g e t e m p e r a t u r e span. Creep s t r e n g t h was d e t e r m i n e d over a r a n g e of t e m p e r a t u r e with the new method of m e a s u r e m e n t u s i n g only a single t e s t s p e c i m e n r a t h e r than a s p e c i m e n at each t e s t t e m p e r a t u r e . The s p e c i m e n was c r e p t at a high t e m p e r a t u r e , and the s t r e s s was a d j u s t e d until a s t e a d y - s t a t e c r e e p r a t e of a p p r o x i m a t e l y 10-5 p e r s was attained. The t e m p e r a t u r e was d e c r e a s e d , and the s t r e s s was i n c r e a s e d until the c r e e p r a t e was a g a i n about 10-5 p e r s. T h i s p r o c e d u r e was r e p e a t e d u n t i l the e n t i r e s t r e s s - t e m p e r a t u r e p r o f i l e had b e e n d e t e r m i n e d . All s p e c i m e n s were i n i t i a l l y held at 3000~ (1649~ for 30 m i n to allow the s t r u c t u r e to s t a b i l i z e before b e g i n ning the t e s t s . The t i m e r e q u i r e d to a t t a i n s t e a d y - s t a t e c r e e p after load a d j u s t m e n t s v a r i e d f r o m a l m o s t z e r o to about 60 m i n (3600 s). In g e n e r a l , the longer t i m e s were r e q u i r e d at the lower t e m p e r a t u r e s . S t e a d y - s t a t e c r e e p was m a i n t a i n e d for about 20 rain (600 s). T e s t s were conducted in a v a c u u m of 10 -7 to 10 -8 T o r r (1.3 • 10 -5 to 1.3 • 10 -6 N / m 2) and both s t r a i n and load were c o n t i n u o u s l y m e a s u r e d and a u t o m a t i c a l l y r e c o r d e d . The v a c u u m c r e e p t e s t i n g m a c h i n e was equipped with a h i g h - t e m p e r a t u r e s t r a i n e x t e n s o m e t e r and a F u l l m a n type l e v e r a r m . 1 The t r u e s t r e s s was d e t e r m i n e d f r o m the load by allowing for the r e d u c t i o n in s p e c i m e n c r o s s s e c t i o n induced by s p e c i m e n elongation. This t e s t t e c h nique is d e s i g n a t e d as " s i n g l e s p e c i m e n m e t h o d " in this p a p e r , and the c o n v e n t i o n a l method which r e q u i r e s a d i f f e r e n t s p e c i m e n and s e p a r a t e t e s t at each t e m p e r a t u r e is d e s i g n a t e d as " m u l t i p l e s p e c i m e n m e t h o d . " C o m p a r i s o n of Methods The single and m u l t i p l e s p e c i m e n methods were c o m p a r e d u s i n g