Carbide reinforcement in two directionally solidified alloyed nickel eutectic alloys
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recently has been observed that directionally solidflied eutectlcs comprised of monocarbide fibers in a nlckel-base matrix have excellent elevated temperature tensile strengths. L e m k e y and Thompson, ~ for example, report tensile strengths on the order of 70,000 psi (482 m n / m z) at 760~ for a eutectic of NbC fibers in an unalloyed nickel matrix, while Bibring, Seibel, and Rabinovitch ~ r e p o r t at the s a m e t e m p e r a t u r e a value of approximately 140,000 psi (964 m n / m a) for a eutectic a l loy consisting of TaC fibers in a y (Ni solid solution)y ' [Ni s (A1, Tl)] superalloy matrix. Walter and Cllne s have shown, however, for two T a C - r e i n f o r c e d nickel alloys having a y - ? ' superalloy m a t r i x that the 1000~ tensile strengths a r e only 3600 and 12,000 psi (24.8 and 83.0 n m / m 2) g r e a t e r than those of two directionally solidified alloys having the s a m e nominal compositions as the m a t r i c e s of the two r e s p e c t i v e eutectic alloys. A study, therefore, was undertaken to evaluate the carbide fiber strengths and the degree of r e i n f o r c e ment in two directionally solidified alloyed nickel eutectics. This p a p e r p r e s e n t s the r e s u l t s of the m e chanical p r o p e r t y study, d e s c r i b e s the techniques used to determine carbide fiber breaking strengths, and e s tablishes that significant fiber strength differences exist for the two eutectic alloys at both room t e m p e r a t u r e and 1000~ Two alloyed nickel eutectics were chosen for evaluation. One alloy has a two-phase T-T~ matrix, while the second has a single-phase y matrix. Mechanical p r o p e r t i e s and m i c r o s t r u c t u r e s of these two eutectic alloys were compared to those of two directionally solidified alloys having the s a m e nominal m a t r i x composition but to which tantalum and carbon had not been added. Nominal compositions of the four a11oys are given in Table I.
EDWARD R. BUCHANAN and LEMUEL A. TARSHIS arc Metallurgist, Physical Metallurgy Branch, and Manager, Properties Branch, respectively, Corporate Research and Development Center, General Electric Company, Schenectady, N. Y. 12301 Manuscript submitted November 3, 1972. METALLURGICAL TRANSACTIONS
Table I.Nominal Compositions of Study Alloys (w/o) Identification
Ni
Cr
Al
Ti
Ta
C
TY' matrix pair; Eutectic alloy Matrix alloy
bal. bal.
10.0 11.9
5.0 6.0
1.O 1.2
14.9 0
1.1 0
7 matrix pair; Eutectic alloy Matrix alloy
bal. bal.
10.O 11.9
0 0
0 0
14.9 0
0
1.1
EXPERIMENTAL PROCEDURE A. Melting One pound heats of each alloy were vacuum-induction melted in an MgO crucible, poured into -~ in. (1.9 cm) diam copper molds, and subsequently r e m e l t e d and directionally solidified in a -~ in. (2.22 cm) diam alumina crucible at ~ in. p e r hr (0.635 cm p e r hr). The length of the final ingot was 4 to 5 in. (10 to 12.5 cm). Metallographlc examination of polished planes prepared parallel to the growth direction reveal four microstructuraUy distinct regions in both eutectic alloys.
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