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The influence of molybdenum on the γ/’phase in experimental nickel-base superalloys

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Abstract

The influence of 1, 3, and 5 at. pct Mo on the γ’precipitate has been studied in experimental wrought nickel-base superalloys containing about 14 at. pct Cr and 6-1/2, 9, or 12 at. pct Al, or 2 at. pct Al plus 4 at. pct Ti. Concentrations of all other elements were quite low to limit the observed effects to those of molybdenum alone. Molybdenum markedly increases the γ’ solvus temperature, as determined by the sensitive and relatively simple technique of differential thermal analysis; correspondingly, the weight fraction of γ’ increases with molybdenum additions for a given aging treatment. Molybdenum dissolves extensively in the γ’of the titanium-free alloys, but it dissolves to a considerably smaller extent in the γ’of the titanium-bearing alloys. Molybdenum substitutes for chromium in y’, but does not alter the aluminum or titanium contents of this phase. Lattice parameters of both the matrix and the γ’are increased markedly by molybdenum, in proportion to the molybdenum contents of these phases. The resulting effects on lattice-parameter mismatch correlate rather well with observed γ’morphology, which tends to change from spheroidal to cuboidal in titanium-free alloys, and from cuboidal to spheroidal in 2 at. pct Al-4 at. pct Ti alloys, as molybdenum is added to these alloys.

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J. W. Freeman was formerly Professor of Metallurgical Engineering, University of Michigan, Ann Arbor, Mich. (Deceased, November, 1970).

This paper is based upon a thesis submitted by W. T. Loomis in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Horace H. Rackham School of Graduate Studies, The University of Michigan.

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Loomis, W.T., Freeman, J.W. & Sponseller, D.L. The influence of molybdenum on the γ/’phase in experimental nickel-base superalloys. Metall Trans 3, 989–1000 (1972). https://doi.org/10.1007/BF02647677

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