Working Paper Article Version 1 This version is not peer-reviewed

Effect of W on the Evolution of Precipitates in Ni-Co-Cr-W-Mo Super-Alloys

Version 1 : Received: 15 September 2019 / Approved: 16 September 2019 / Online: 16 September 2019 (01:22:39 CEST)

How to cite: Bao, H.; Gong, Z.; Chen, Z.; Yang, G.; Liu, Z. Effect of W on the Evolution of Precipitates in Ni-Co-Cr-W-Mo Super-Alloys. Preprints 2019, 2019090156 Bao, H.; Gong, Z.; Chen, Z.; Yang, G.; Liu, Z. Effect of W on the Evolution of Precipitates in Ni-Co-Cr-W-Mo Super-Alloys. Preprints 2019, 2019090156

Abstract

The Ni-Co-Cr-W-Mo system is critical for the design of nickel-based super-alloys. This system stabilizes different topologically close packed (TCP) phases in many of the commercially super-alloys with high W and Mo contents. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermodynamic calculations are applied to investigate the thermodynamics of the precipitates in two different W content Ni-Co-Cr-W-Mo super-alloys. Computational thermodynamics verified experimental observation of the f u phase formation as a function of temperature and alloy chemistry, but the kinetics for the precipitation of M6C phase do not agree with the experimental findings. The major precipitates of alloy 1 at temperatures 700 and 750 °C during long time exposure are M23C6, γ′ phase, and MC, and alloy 2 are M23C6, γ′ phase, MC, M6C and u phase. The W addition is found to promote the precipitation of M6C and u phase during exposure. The M6C has higher W and lower Ni content than that of u phase, meanwhile, M6C is an unstable phase would transform into M12C after 5000 h exposure at 750 °C. A great quantity of needle-like u phases precipitated after exposure at 750 °C for 5000h, which have no effect on the impact property of alloy 2.

Subject Areas

nickel-based super-alloys; M6C; u phase; long time exposure; M12C

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