Load-Signature analysis for pack rolling of near-gamma titanium aluminide alloys
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Ni 18.2 18.0
C-300 T-300
Co 8.8 --
Mo 2.9 2.4
Ti 0.7 2.2
Fe balance balance
Table II. Driving Forces (AG/RT) for Precipitation of Phases in C-300 and T-300 Maraging Steel Systems at 510 ~ Thermo-Caic ts~ Thermochemical Calculation Results*
Phase Ni3Ti Ni3Mo
(Fe, Co)2Ti Laves Fe7Mo6/.t, Fcc
Driving Force in C-300 0.95 0.64 -0.82 0.38 0.74
6. L. Kaufman: CALPHAD, 1984, vol. 8, pp. 25-66. 7. G.B. Olson: Northwestern University, Evanston, IL, private communication, 1992.
Driving Force in T-300 1.09 0.33 -0.24 0.42 0.67
*In our earlier calculations (Table X of Ref. 1), fcc austenite was included as a stable phase. The data presented here refer to the decomposition of a bcc matrix, with fcc austenite excluded, which is a more realistic model for the initial stage of decomposition of a maraging steel.
current calculation results and the earlier atom probe experimental analysis data, where Ni3Ti has the highest driving force and is always the phase first to precipitate out from the bcc matrix. The failure to observe Ni3Mo precipitation in C-300 steel is, at first, surprising. However, it should be noted from our earlier atom probe results tll that the initial clusters to form in C-300 were rich in both Ti and Mo. Naturally, kinetics must also play a part in the decomposition process. For example, the formation of austenite (fcc) is delayed until well after precipitation of intermetallics occurs in the case of C-300. In T-300, austenite does not form after very prolonged aging. We consider that the combination of thermochemical calculation with atomic-scale measurement of phase composition now provides a strong basis for future alloy development programs.
The atom probe research in Oxford was supported by the Science and Engineering Research Council (UK) under Grant No. GR/F/06111. WS is grateful to The British Council for financial support. The authors would like to thank Professor G.B. Olson for helpful discussions. REFERENCES 1. W. Sha, A. Cerezo, and G.D.W. Smith: Metall. Trans. A, 1993, vol. 24A, pp. 1221-32. 2. W. Sha, A. Cerezo, and G.D.W. Smith: Metall. Trans. A, 1993, vol. 24A, pp. 1233-39. 3. W. Sha, A. Cerezo, and G.D.W. Smith: Surf. Sci., 1991, vol. 246, pp. 278-84. 4. W. Sha, A. Cerezo, and G.D.W. Smith: J. Phys. Colloq., 1989, vol. 50-C8, pp. 407-12. 5. B. Sundman, B. Jansson, and J.-O. Andersson: Paper presented at ASM Meeting, Orlando, FL, 1986.
METALLURGICAL AND MATERIALS TRANSACTIONS A
Load-Signature Analysis for Pack Rolling of Near-Gamma Titanium Aluminide Alloys S.L. SEMIATIN and V. SEETHARAMAN Titanium-aluminide alloys based on the ordered equiatomic TiA1 phase are receiving increasing attention as candidates for advanced aerospace applications, t~1 Of greatest interest are the so-called near-gamma alloys, which contain a small amount (typically 10 to 20 pct) of the ordered alpha-two, or Ti3A1, phase. With proper control of the microstructure, such materials possess a good blend of elevated temperature strength and creep resistance and a modicum of ambient temperature ductility and frac
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