Microstructure evolution and mechanical properties of NiAlCrFeMo high entropy superalloy after different annealing treatment

Abstract

A novel NiAlCrFeMo high entropy superalloy was prepared using the vacuum arc melting method, followed by annealing at 800 °C, 1000 °C, and 1200 °C for 10 h. The microstructural characteristics and mechanical properties of the alloy after annealing were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Vickers hardness testing, and high-temperature tensile testing. The results indicate that the as-cast alloy consists of dendritic γ+γ′ phases and interdendritic B2-type β phase, with hemispherical α-Cr phases present within the β phase. Compared to the as-cast status, the volume fraction of the β phase in the annealed state increased from 18.52 % to 26.13 %. Notably, at 800 °C/10h, acicular γ_p’ phases precipitated within the β phase. The alloy exhibited varying degrees of improvement in both strength and ductility after annealing. The specimen annealed at 800 °C/10h showed the highest strength (σ_YS = 181.06 MPa) and good ductility (ε_EI = 12.45 %), with strength increasing by approximately 13.10 % compared to the as-cast status. This improvement is attributed to the coarsening of the α-Cr phase, the transformation in γ′ morphology, and the precipitation of acicular γ_p’ phase. At 1200 °C/10h, all precipitates dissolved into the matrix, resulting in the lowest strength (σ_YS = 134.08 MPa) and the highest ductility (ε_EI = 15.54 %).