Alloying element effects in metastable beta titanium alloys
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Alloying Element Effects in Metastable Beta Titanium Alloys C. F. YOLTON,
F. H. FROES,
AND
R. F. MALONE
T h i s c o m m u n i c a t i o n p r e s e n t s the r e s u l t s of a s t e p wise m u l t i p l e l i n e a r r e g r e s s i o n a n a l y s i s of the effect of c h e m i s t r y on the b e t a t r a n s u s t e m p e r a t u r e and the C - c u r v e nose t i m e and t e m p e r a t u r e for alpha p r e c i p i t a t i o n , for the m e t a s t a b l e b e t a c l a s s of t i t a n i u m a l l o y s . T h e data r e p o r t e d should allow the d e s i r e d t r a n s f o r m a t i o n c h a r a c t e r i s t i c s to be d e s i g n e d into new a l l o y s of this c l a s s . T h i s will i n s u r e adequate h a r d e n i n g in thick s e c t i o n s and c o m p a t i b i l i t y with t h e r m a l cycle e x p o s u r e . E x a m p l e s of the l a t t e r a r e f a b r i c a t i o n ( e . g . , i s o t h e r m a l forging, s u p e r p l a s t i c f o r m i n g , hot i s o s t a t i c p r e s s i n g ) and j o i n i n g ( e . g . , b r a z i n g , diffusion bonding). The a n a l y s i s was c a r r i e d out on s e v e n t y a l l o y s . The m a j o r i t y of t h e s e a l l o y s have c o m p o s i t i o n s which a r e c h a r a c t e r i s t i c of lean m e t a s t a b l e b e t a (Table I). Beta t r a n s u s t e m p e r a t u r e s were d e t e r m i n e d by the d i s a p p e a r i n g p h a s e method. I n this method, s a m p l e s a r e f i r s t aged to p r e c i p i t a t e alpha p h a s e . T h e y a r e then r e h e a t e d to v a r i o u s t e m p e r a t u r e s s e p a r a t e d by C. F. YOLTON and R. F. MALONE are Associate Engineer and Consulting Engineer, respectively, Colt Industries, Crucible Research Center, Pittsburgh, PA 15230. F. H. FROES formerly Manager, Titanium Research and Development at Crucible Research Center, is now Titanium Group Leader at the Air Force Materials Laboratory, Wright-Patterson Air Force Base, Dayton, OH 45433. Manuscript submitted May 2, 1978. 132-VOLUME 10A, JANUARY 1979
Table I. Characteristics of Alloys Investigated Parameters *
Alloy,st
Mean $
Min
Max
Mo Al Sn
63 62 25
7.7 2.5 4.5
2.0 1.0 2.0
13.0 6.0 11.0
Zr V Cr Mn Fe Si /~rr (~ Tn (~ t n (s)
20 25 14
3.7 6.8 4.0
2.0 3.0 2.0
6.0 12.0 6.0
2
1.4
1.0
2.0
3 5
1.6 0.3 825 575 43
1.0 0.2 720 455 2
2.0 0.5 940 800 600
-
*Alloy elements in wt pct. tNumber of alloys out of the total seventy alloys studied. :~Mean for alloys containing the element.
15~ i n t e r v a l s , held for 15 m i n at t e m p e r a t u r e and w a t e r quenched. The b e t a t r a n s u s t e m p e r a t u r e is then n o m o r e than 15~ above the highest t e m p e r a t u r e for which alpha phase was detected m e t a l l o g r a p h i c a l l y . T h i s 15~ i n t e r v a l can be f u r t h e r r e d u c e d somewhat by e s t i m a t i n g v o l u m e f r a c t i o n s of a phase. T a b l e I s u m m a r i z e s the b e t a t r a n s u s t e m p e r a t u r e s of the a l l o y s . T r a n s f o r
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