The Ni–Co–Cr–W–Mo system is critical for the design of nickel-based superalloys. This system stabilizes different topologically close-packed (TCP) phases in many commercially superalloys with high W and Mo contents. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermodynamic calculations were applied to investigate the thermodynamics of the precipitates in two different W-contained Ni–Co–Cr–W–Mo superalloys (Alloy 1 and Alloy 2). Computational thermodynamics verifies the experimental observation of the μ phase formation as a function of temperature and alloy chemistry, but the kinetics for the precipitation of the M 6 C phase do not agree with the experimental findings. The major precipitates of Alloy 1 at temperatures of 700 °C and 750 °C during long-time exposure are M 23 C 6 , γ′ phase and MC; for Alloy 2, they are M 23 C 6 , γ′ phase, MC, M 6 C and μ phase. W addition is found to promote the precipitation of M 6 C and μ phase during exposure. M 6 C has higher W and lower Ni content than μ phase, whereas M 6 C is an unstable phase that would transform into M 12 C after 5000-h exposure at 750 °C. A great quantity of needle-like μ phases precipitated after exposure at 750 °C for 5000 h, which have no effect on the impact properties of Alloy 2.

中文翻译：

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不同钨含量的 Ni-Co-Cr-W-Mo 高温合金中析出物的演变

Ni-Co-Cr-W-Mo 系统对于镍基高温合金的设计至关重要。该系统稳定了许多具有高 W 和 Mo 含量的商业高温合金中的不同拓扑密堆积 (TC​​P) 相。应用扫描电子显微镜 (SEM)、透射电子显微镜 (TEM) 和热力学计算来研究两种不同的含钨 Ni-Co-Cr-W-Mo 高温合金（合金 1 和合金 2）中析出物的热力学。计算热力学验证了 μ 相形成随温度和合金化学变化的实验观察，但 M 6 C 相的析出动力学与实验结果不一致。合金1在700℃和750℃长期暴露时的主要析出物是M 23 C 6 、γ′相和MC；对于合金 2，它们是M 23 C 6 、γ'相、MC、M 6 C和μ相。发现W添加促进了M 6 C和μ相在暴露期间的沉淀。M 6 C 比 μ 相具有更高的 W 和更低的 Ni 含量，而 M 6 C 是一种不稳定相，在 750 °C 下暴露 5000 小时后会转变为 M 12 C。在 750 °C 下暴露 5000 h 后会析出大量针状 μ 相，这对合金 2 的冲击性能没有影响。