Solid solution softening and strain-rate sensitivity of Fe-Re and Fe-Mo alloys
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University of British Columbia, Vancouver, Canada. M. E. FINE is Professor, Dept. of MaterialsScience,Northwestern University, Evanston, IU. 60201. Manuscript submitted September 17, 1973. METALLURGICAL TRANSACTIONS
additions f i r s t i n c r e a s e d the strength but f u r t h e r a d d i tions r e s u l t e d in solid solution softening. By m e a s u r ing the s t r a i n - r a t e s e n s i t i v i t y as well as the flow s t r e s s , it was p o s s i b l e to divide the flow s t r e s s into a s t r a i n r a t e s e n s i t i v e p a r t and a n o n - s t r a i n r a t e s e n s i t i v e p a r t and it was shown that the solid solution softening o b s e r v e d at r e d u c e d t e m p e r a t u r e s was mainly a s t r a i n r a t e s e n s i t i v e phenomenon. It is the purpose of the p r e s e n t p a p e r to r e p o r t data concerning the F e - M o and F e - R e s y s t e m s to substantiate the r e s u l t s for F e - T i . Me and Re have different a t o m i c radii than Ti and diff e r e n t affinities for i n t e r s t i t i a l s . F u r t h e r , the a l l o y s were t r e a t e d with wet H 2 to r e m o v e i n t e r s t i t i a l i m p u r i t i e s and to t h e r e b y r e d u c e any effects due to scavenging.
EXPERIMENTAL
PROCEDURE
Six Fe-Mo and four Fe-Re alloys well within the solubility l i m i t s , 3.8 at. pct and 11 at. pet r e s p e c t i v e l y at 600~ were made in an a r c melting furnace using a cold copper h e a r t h and n o n - c o n s u m a b l e tungsten e l e c t r o d e . The s t a r t i n g m a t e r i a l was Glidden A104 Fe, F a n s t e e l Company Me w i r e and Spex I n d u s t r i e s Re. The compositions of the a l l o y s a r e given in Table I. The a t m o s p h e r e was p u r i f i e d argon purged by melting a titanium button b e f o r e each melting or r e m e l t i n g . To a s s u r e homogeneity each ingot was r e m e l t e d at l e a s t t h r e e t i m e s . The castings which weighed 20 to 40 g r a m s were cold r o l l e d to about 1 mm thickness, machined into s p e c i m e n s 3.2 mm wide and 25.4 mm gage length, c h e m i c a l l y cleaned in a solution of 5 ml HF, 80 ml H~O2, and 15 ml H20 maintained below 20~ in an ice bath and finally annealed for 7 h at 800~ in a dynamic wet hydrogen a t m o s p h e r e (2 cubic feet p e r h flow) to r e d u c e the i n t e r s t i t i a l content. Unalloyed iron s a m p l e s were p r e p a r e d by the s a m e technique. The Fe and a l loys so t r e a t e d did not show s t r a i n aging. The final g r a i n s i z e in the s a m p l e s was 60 • 15/z, m e a s u r e d on four s e c t i o n s of each alloy. The t e n s i l e t e s t i n g was done at a s t r a i n r a t e , 4, of 3.3 • 10-S/sec. The yield s t r e s s , ay, was computed f r o m the load at the i n t e r s e c t i o n of the s t r a i g h t lines e x t r a p o l a t e d f r o m the e l a s t i c and p l a s t i c portions of the l o a d - e l o n g a t i o n c u r v e s . When a yield point o c c u r r e d , as o c c u r r e d with low Ti, F e
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