长期时效条件下Cr、Mo、W对DD98M合金铸态组织与性能的影响

基于团簇加连接原子模型和镍基高温合金理想成分式,对DD98M合金进行成分解析和再设计,降低Cr/Mo/W元素含量,得到DD98MC合金。利用真空感应熔炼制备两种合金的母合金,并进行固溶时效和1273k下的长期时效。采用X射线衍射(XRD)、扫描电镜(SEM)、电子探针(EPMA)等测试方法对两种合金时效后的铸态组织进行研究,分析高温长期时效和Cr/Mo/W对合金铸态组织和性能的影响规律。结果表明,长期时效会引起γ"相的部分分解,促进元素扩散,加剧元素偏析。随长期时效时间的延长,γ"相粗化长大乃至出现筏化,硬度降低,错配度绝对值减小,γ"相立方度降低。随Cr/Mo/W元素含量降低,错配度绝对值减小,γ"相立方度降低,硬度降低。DD98M合金长期时效出现了γ"相筏化,在晶界和晶内有粗大的γ"相形成和大量的σ相析出。 DD98MC合金长期时效只在晶界处有σ相和MC型碳化物析出。与DD98M相比DD98MC有更好的组织稳定性和机械性能。

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

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.