Some observations on the structure of Ti-11.5 Mo-6 Zr-4.5 Sn (Beta III) as affected by processing history
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Some Observations on the Structure of Ti-11.5 Mo-6 Zr-4.5 Sn (Beta III) as Affected by Processing History J . C. WILLIAMS, F. H. FROES, AND C. F . YOLTON There have been a number of a r t i c l e s written on the s t r u c t u r e and p r o p e r t i e s of the metastable b e t a titanium alloy T i - l 1 . 5 M o - 6 Z r - 4 . S S n (Beta III). 1-~* S e v e r a l of these have made sound contributions to the understanding of the s t r u c t u r e and p r o p e r t i e s of the alloy in the heat t r e a t e d conditions studied. Howe v e r , many have not a d d r e s s e d the questions of optimum p r o c e s s i n g and heat t r e a t m e n t as viewed f r o m an a p p l i c a t i o n ' s standpoint. Accordingly, the alloy has been v a r i o u s l y r e p o r t e d to have p o o r e r t e n s i l e ductility, 4'7 lower s t r e s s c o r r o s i o n r e s i s t a n c e , 5 and p o o r e r toughness than is typical when p r o p e r p r o c e s s ing conditions a r e used. F u r t h e r m o r e , in some c a s e s the d e t a i l s of the m i c r o s t r u c t u r a l a n a l y s i s a p p e a r to be in conflict and in other c a s e s the i n t e r p r e t a t i o n given to some of these r e s u l t s w a r r a n t s c l o s e r s c r u tiny with r e g a r d to t h e i r c o r r e c t n e s s and g e n e r a l a p p l i c a b i l i t y .%6,7 F o r example, Ganesan et al7 suggest J. C. WILLIAMS is Professor, Department o f Metallurgy and Materials Science, Carnegie-Mellon University, Schenley Park, Pittsburgh, PA ! 5213. F. H. FROES, formerly with Colt Industries, is now at Air Force Materials Laboratory, Wright-Patterson AFB, OH 45433. C. F. YOLTON, is Associate Engineer, Titanium Research and Development, Colt Industries/Crucible Materials Research Center, Pittsburgh, PA 15230. Manuscript submitted February 7, 1978. 3 5 6 - V O L U M E l l A , FEBRUARY 1980
that co-phase p r e c i p i t a t e s i n / 3 - g r a i n boundaries, yet many other studies have shown that w-phase o n l y is uniformly nucleated w h e r e a s a - p h a s e is always the heterogeneous nucleation product. 12'13 F u r t h e r , the effects that spontaneous r e l a x a t i o n in thin foils have on the a p p a r e n t m i e r o s t r u c t u r e a r e now well-known and have been extensively documented. 1%~5 Despite this, the latent effects of such thin foil a r t i f a c t s have been d e s c r i b e d in length 6 even though t h e r e a p p e a r s to be no c o r r e l a t i o n between these effects and bulk material behavior. The purpose of this communication is to d e s c r i b e the optimum p r o c e s s i n g for Beta III, to d e m o n s t r a t e the effect of such p r o c e s s i n g on m e c h a n i c a l p r o p e r t i e s and to c o r r e c t s e v e r a l e r r o n e o u s notions r e g a r d ing m i c r o s t r u c t u r a l d e t a i l s of the alloy. Since Beta HI is g e n e r i c a l l y known as a m e t a s t a b l e beta alloy, many i n v e s t i g a t o r s have been tempted to s t a r t with the alloy in the fully m e t a s
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