Effect of Cr,Mo and W on the As-Cast Microstructure and Properties of DD98M Alloy During Long-Term Aging
Based on the"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 1273 K.The as-cast microstructure of the two alloys after aging was studied by XRD,SEM and 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 coarsens 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,coarse γ'phases form and a large amount of σ phase precipitate 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.
DD98Mcluster plus connected atom modelas-cast microstructurelong-term agingCr/Mo/W
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