The constitution of metastable titanium-rich Ti-Fe alloys:An order-disorder transition
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EXPERIMENTAL
METHODS
AND
RESULTS
Experimental details regarding alloy preparation, the splat quenching process, and X-ray diffraction methods utilized follow those described previously, z~ The alloys were prepared from iodide grade titanium and iron of 99.95 pct purity. The splat cooling unit used has also been described in detail, z~ The estimated cooling rates 12 range from 106 to I08~ per sec. The compositions of the alloys studied are listed in Table I, together with their equilibrium structures, and the phases retained upon splat cooling to room temperature. The resulting metastable phases completely cover the composition range investigated. They are either a TiFe(Ti) solid solution or a ~-Ti(Fe) solid solution, as described below. Lattice parameters are given in Table I. A single phase TiFe(Ti) was retained in the splat R. RAY, formerly Research Assistant, Department of Metallurgy and Materials Science, Massachusetts Institute of Technology, Cambridge, Mass., is now Research Associate, Department of Mechanical Engineering and Department of Chemistry, Northeastern University, Boston, Mass. B. C. GIESSEN, formerly Research Associate, Department of Metal~urgy and Materials Science, Massachusetts Institute of Technology, is now Associate Professor, Department of Chemistry, Northeastern University. N. J. GRANT is Professor, Department of Metallurgy and Materials Science, Massachusetts Institute of Technology. Manuscript submitted December 14, 1970. METALLURGICAL TRANSACTIONS
cooled Ti-Fe alloys with compositions from about 37.5 t o 50 a t . p c t F e . X - r a y d i f f r a c t i o n a n a l y s i s s h o w e d t h i s to b e a m e t a s t a b l e , n o n s t o i c h i o m e t r i c s o l i d s o l u t i o n b a s e d on T i F e . L a t t i c e p a r a m e t e r v a l u e s of t h i s p h a s e a r e p l o t t e d a g a i n s t c o m p o s i t i o n in Fig. I. S p l a t c o o l e d T i - F e a l l o y s w i t h < 37.5 a t . p c t F e w e r e a l s o s i n g l e p h a s e a n d c o n s i s t e d e i t h e r of T i F e ( T i ) o r / 3 - T i ( F e ) . A d i s t i n c t i o n on t h e b a s i s of X - r a y d a t a w a s n o t p o s s i b l e d u e t o t h e a b s e n c e of s u p e r s t r u c t u r e l i n e s ; however, as shown below, it can be inferred that splat c o o l e d a l l o y s w i t h l e s s t h a n a b o u t 35 a t . p c t F e c o n s i s t of d i s o r d e r e d ~3-Ti(Fe). T h e l a t t i c e p a r a m e t e r v a l u e s of t 3 - T i ( F e ) a r e p l o t t e d in F i g . 1 ( s o l i d c i r c l e s ) ; they decrease uniformly with increasing iron content and lie on a smooth curve joining the lattice parameter v a l u e s of T i F e ( T i ) s o l i d s o l u t i o n s ( o p e n c i r c l e s ) . T h e l a t t i c e p a r a m e t e r of p u r e / 3 - t i t a n i u m a t 20~ also s h o w n in F i g . 1, w a s c a l c u l a t e d f r o m t h e v a l u e m e a s u r e d a t 9 0 0 ~ 8 L a t t i c e p a r a m e t e r s of f 3 - T i ( F e ) s o l i d s o l u t i o n s [ r e t a i n e d b y c o n v e n
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