Densification mechanism transition, microstructure evolution and mechanical behavior of EP741NP superalloy via hot-pressed sintering

Abstract

EP741NP Ni-based superalloy with remarkable mechanical properties is widely applied in the aerospace industry. Here, the effects of sintering temperature on the densification mechanism transition, microstructure and tensile properties of hot-pressed EP741NP Ni-based superalloy are revealed. The critical relative density, corresponding to densification mechanism transition, shifts from 0.71 to 0.80 as the sintering temperature increases from 1130 °C to 1230 °C, which is calculated by a proposed model considering the equality of localized contact pressure between particles and overall yield stress. The contribution of macroscopic plastic deformation to the overall densification increases as the sintering temperature rises due to the exacerbated material softening. The densification activation energy of the EP741NP superalloy is obtained as 377.07 kJ/mol. The initial dendritic structure, primary particle boundaries and voids are gradually eliminated as the sintering temperature rises, while the volume fraction of γ′ phase decreases due to the phase dissolution. Due to the balance between densification level and grain size, the sample hot pressed at 1180 °C exhibits the best synergy of strength and ductility at room temperature and 650 °C, accompanied by more characteristics of ductile fracture. Our work provides insights into the development of advanced Ni-based superalloys at elevated temperatures.