Effect of Cr, Mo ,W on the as-cast microstructure and properties of DD98M alloy during long-term aging

Abstract:

Based on this "cluster plus connected atoms" model and the ideal composition formula of nickel-based superalloys, the element content of Cr/Mo/W of DD98M alloy was reduced, and the DD98MC alloy was obtained. The parent alloys of the two alloys were prepared by vacuum induction melting. Then they were subjected to solution aging and long-term aging at 1273k. The as-cast microstructure of the two alloys after aging was studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The effects of long-term aging at high temperature and Cr/Mo/W on the as-cast microstructure and properties of the alloys were analyzed. The results show that long-term aging causes partial decomposition of γ" phase, promotes element diffusion and intensifies element segregation. With the extension of long-term aging time, γ" phase coarsen or even becomes rafting, the hardness decreases, the absolute value of misfit decreases, and the cubic degree of γ" phase decreases. As the content of Cr/Mo/W elements decreases, the absolute value of misfit decreases, the cubic degree of γ" phase decreases and the hardness decreases. Under long-term aging, the γ" phase of DD98M alloy becomes rafting. Meanwhile, there are coarse γ" phase formation and a large moment of σ phase precipitation in grain boundaries and grains. Under long-term aging, for the DD98MC alloy, only σ phase and MC carbide precipitate in grain boundaries. Compared with the DD98M, the DD98MC has better structural stability and mechanical properties.

Key words:DD98M; cluster plus connected atom model; as-cast microstructure; long-term aging; Cr/Mo/W