Composition design, phase transitions of a new polycrystalline Ni-Cr-Co-W base superalloy and its isothermal oxidation dynamics behaviors at 1300°C

Publication date: 5 September 2017
Source:Materials & Design, Volume 129
Author(s): Yubi Zhang, Xiaoyang Hu, Changrong Li, Weiwei Xu, Yongtao Zhao
The composition, phase transitions and isothermal oxidation dynamics of a new polycrystalline Ni-Cr-Co-W base superalloy are investigated using CALculation of PHAse Diagrams (CALPHAD), Differential Scanning Calorimetry (DSC), ThermoGravimetric analysis (TG/dTG), Scanning Electron Microscope and Energy Dispersion Spectrum (SEM/EDS) methods. The microstructure of the designed alloy shows a uniform γ matrix with the precipitates of rich-Ti cellular η and rich-Nb acicular platelet δ phase, and no Topologically Close-packed Phases (TCPs) observed, and the oxide behavior obeys a parabolic law with a parabolic constant (kp) 2.945mg²/(cm⁴·h) at isothermal 1300°C for 30 hours. The oxide scales are composed of an outer loose oxide mixture containing Cr, Ni, Ti and Nb/Ta and generous pores presented for a volatilization of Cr2O3, and a dense aluminum-rich oxide layer.

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