Morphology of y’ and y” precipitates and thermal stability of inconel 718 type alloys
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The precipitation of the γ’ (Ll2) and γ" (DO22) phases has been studied in four alloys Fe-Ni-Cr-Ti-Al-Nb containing a higher Ti + Al/Nb ratio than that of the INCONEL 718 alloy. For these alloys, the precipitation microstructure varies rapidly with aging temperature and composition. Bct γ"particles have always been found to precipitate on γ’ phase. Moreover, by aging three alloys above a critical temperature, a “compact ntorphology” has been observed: cube-shaped γ’ particles coated on their six faces with a shell of γ" precipitate. This microstructure has proved to be very stable on prolonged aging. A thermal stability better than that encountered in nominal INCONEL 718 alloy can thus be achieved. The influence of composition and aging temperature on the conditions that bring about this “compact morphology” has been investigated. A minimal Ti + Al/Nb ratio between 0.9 and 1 has been determined, allowing the “compact morphology” to be obtained.
KeywordsMetallurgical Transaction Aging Time Aging Temperature Field Image Dark Field
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- 1.D. F. Paulonis, J. M. Oblak, and D. S. Duvall:Trans. ASM, 1969, vol. 62, p. 611.Google Scholar
- 2.I. Kirman and D. H. Warrington:J. Inst. Metals, 1971, vol. 99, p. 197.Google Scholar
- 3.0. H. Kriege and J. M. Baris:Trans. ASM, 1969, vol. 62, p. 195.Google Scholar
- 4.H. L. Eiseilstein:Amer. Soc. Testing Mater., Spec. Tech. Rpt., 1965, no. 369.Google Scholar
- 5.H. J. Wagner and A. M. Hall: DMIC Report, 1965, no. 217.Google Scholar
- 8.J. P. Michal:Mem. Sei. Rev. Met., 1971, vol. 11, p. 785.Google Scholar
- 9.G. R. Speich:Trans. TMS-AIME, 1962, vol. 224, p. 850.Google Scholar