Correlation of structure and superconducting properties in Nb(Cb)-Ti quaternary alloys
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S U P E R C O N D U C T I N G N b - T i alloys of v a r i o u s oxygen c o n t e n t s are p r e s e n t l y b e i n g used in high m a g n e t i c field dc solenoids. T h e u t i l i t y of these alloys depends on their ease of f a b r i c a b i l i t y , the c r i t i c a l value of m a g n e t i c field, Hr, n e c e s s a r y to d e s t r o y s u p e r c o n d u c t i v i t y , and the m a x i m u m c u r r e n t d e n s i t y , Jc, that the m a t e r i a l can c a r r y b e f o r e r e v e r t i n g to the n o r m a l state. It i s g e n e r a l l y true that a l l o y s of higher n i o b i u m c o n t e n t (45 to 60 wt pct Nb) a r e m o r e r e a d i l y f a b r i c a t e d and have higher v a l u e s of c r i t i c a l field. After optimum thermomechanical processing, however, h i g h e r t i t a n i u m content a l l o y s (35 to 45 wt pct Nb) show l a r g e r c r i t i c a l c u r r e n t d e n s i t i e s at i n t e r m e d i a t e m a g n e t i c fields (20 to 80 kg). T o o p t i m i z e the e c o n o m i c s of solenoid c o n s t r u c t i o n , it is t h e r e f o r e d e s i r a b l e to i) i n c r e a s e Jc i n high n i o b i u m - c o n t a i n i n g a l l o y s without l e s s e n i n g f a b r i c a b i l i t y or Hr, or ii) i m p r o v e the f a b r i c a b i l i t y and i n c r e a s e Hr in alloys of lower niobium content without d e c r e a s i n g Jc. R e u t e r , R a l l s , and Wulff 1 showed that i m p r o v e m e n t s of Jc in 60 wt pct Nb a l l o y s c a n be affected by i n c r e a s e s in oxygen content. The optimum t h e r m a l aging t r e a t m e n t for alloys c o n t a i n i n g about 2500 ppm O was found to be a p p r o x i m a t e l y 525~ In an e x t e n s i o n of this work, Rauch, C o u r t n e y , and Wulff z found that, for a l l o y s of this n i o b i u m l e v e l , the o p t i m u m aging t e m p e r a t u r e depended s t r o n g l y on oxygen content; the l e s s e r the i n t e r s t i t i a l l e v e l s the lower the o p t i m u m aging t e m p e r a t u r e . T h i s i n v e s t i g a t i o n f u r t h e r showed that the m a x i m u m o b t a i n a b l e v a l u e s of Hr d e c r e a s e d with i n c r e a s e s in oxygen content. R. L. RICKETTS,formerly Research Assistant, Department of Metallurgy and MaterialsScience, M.I.T., Cambridge,Mass., is Research Associate General Electric Company, Schenectady, N.Y.T.H. COURTNEY formerly Research Associate, Department of Metallurgy and Materials Science, M.I.T., is Associate Professor, Department of Mechanical Engineering,The University of Texas at Austin, Austin. Tex. L. A. SHEPARD formerly Research Associate, Department of Metallurgy and Materials Science, M.I.T., is Research Associate Army Materials Research Center, Watertown, Mass. J. WULFF is Professor Emeritus, Department of Metallurgy mad Materials Science and Center for Materials Science and Engineering, M.I.T. Manuscript submitted November 7, 1969. METALLURGICALTRANSACTIONS
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