On the equilibrium silicide in beta Ti-V alloys containing Si
- PDF / 699,200 Bytes
- 3 Pages / 612 x 792 pts (letter) Page_size
- 37 Downloads / 168 Views
G. W. FRANTI and D. A. KOSS are Postdoctoral Research Associate and Professor, respectively, Department of MetallurgicalEngineering, MichiganTechnological University, Houghton, MI 49931 Manuscript submitted February 14, 1977. METALLURGICALTRANSACTIONSA
typical selected area electron diffraction patterns obtained by t i l t i n g the s a m p l e to excite both p r e c i p i tate and m a t r i x r e f l e c t i o n s , S i m i l a r d i f f r a c t i o n patt e r n s have b e e n obtained f r o m s i l i c i d e p r e c i p i t a t e s in a T i - 3 0 V - 1 S i alloy aged for long t i m e s at 570~ 1~ A n a l y s i s of t h e s e and o t h e r p a t t e r n s y i e l d s i n t e r p l a n a r s p a c i n g s c o n s i s t e n t with those d e t e r m i n e d by X - r a y diffraction, Interplanar angles were measured and a g r e e with the c a l c u l a t e d a n g l e s to within one d e g r e e . T h e r e a r e no r e a d i l y i d e n t i f i a b l e m a t r i x p r e c i p i t a t e o r i e n t a t i o n r e l a t i o n s h i p s , although the f a c e t e d a p p e a r a n c e i n d i c a t e s at l e a s t s o m e d e g r e e of coherence, The p r e v i o u s l y r e p o r t e d t e t r a g o n a l Ti3Soi s i l i c i d e p h a s e has l a t t i c e p a r a m e t e r s of a = 10.39A and c = 5.17A, 5 which a r e n e a r those o b s e r v e d (a = 10,02/~ and c = 4.965/~)especially when one notes that v a n a d i u m has a s m a l l e r s i z e than that of t i t a n i u m . E n e r g y d i s p e r s i v e a n a l y s i s by X - r a y s shows that the p a r t i c l e s c o n t a i n a s u b s t a n t i a l a m o u n t of s i l i c o n but the exact c o n c e n t r a t i o n could not be d e t e r m i n e d , We thus conclude that the o b s e r v e d p a r t i c l e s a r e a t e t r a g o n a l s i l i c i d e , p r o b a b l y of the type " ( T i , V)3Si" in a g r e e m e n t with S c h u b e r t e t a l . ~ T h e r e a r e a n u m b e r of r e a s o n s why the t e t r a g o n a l p h a s e a p p e a r s to be the e q u i l i b r i u m s i l i c i d e in this alloy. The o b s e r v a t i o n that t h e s e p a r t i c l e s cause a d i s s o l u t i o n of the t r a n s i t i o n (Ti, V)xSiy (see Fig. 7 of Ref. 8) i n d i c a t e s that the t e t r a g o n a l s i l i c i d e is m o r e s t a b l e . The n u c l e a t i o n of " ( T i , V ) 3 S i " p a r t i c l e s at g r a i n b o u n d a r i e s is c o n s i s t e n t with the n u c l e a t i o n of e q u i l i b r i u m p h a s e s in o r d e r to r e d u c e t h e i r i n t e r f a c i a l e n e r g y t e r m . n No t e t r a g o n a l s i l i c i d e s w e r e s e e n a f t e r a g i n g at 450~ in T i - 3 0 V - 1 S i , which is c o m p a t i b l e with the fact that such p h a s e s a l s o have difficulty n u c l e a t i n g at low a g i n g t e m p e r a t u r e s where the d r i v i n g f o r c e s favor t r a n s i t i o n p h a s e s with s m a l l i n t e r f a c i a l f r e e e n e r g i e s . ~~ P e r h a p s most i m p o r t a n t is the o b s e
Data Loading...
