The effect of heat treatment on the microstructure and mechanical properties of as-cast NiCoCrFeAlW eutectic high entropy alloy

Abstract

This work primarily investigated the influences of heat treatment at different temperatures (600 ℃, 700 ℃, 800 ℃, and 900 ℃) after holding at 1 h, 2 h, 4 h, and 10 h respectively on the mechanical behavior and microstructure of the Ni₃₀Co₃₀Cr₁₀Fe₁₀Al₁₈W₂ eutectic high-entropy alloy, which is characterized by a dual-phase microstructure composed of B2 (NiAl) and FCC (CoCrFeW-rich) phases, were investigated. Precipitation was observed in the B2 phase after heat treatment, with precipitates forming during heat treatment at different temperature between 600 °C and 800 °C. The precipitated phase is FCC phase, which enhances the alloy's strength while reducing its elongation. Meanwhile, at 800 °C, the alloy shows a significant increase in microhardness due to the precipitated phase in BCC phase. With rising temperature, the amount of precipitates, while the size of precipitated phase grows with extended holding time, due to enhanced atomic diffusion and the thermodynamic driving force that promote both nucleation and coarsening of the precipitated phase. After holding at 900 ℃, the CoCrFe precipitated phase (FCC) dissolve in the NiAl phase (B2), softening the sample and resulting in an increase in elongation, and the alloy still exhibits favorable tensile properties. This study mainly investigates influence on the microstructure and tensile strength of the alloy. Meanwhile, the precipitation mechanism in Ni₃₀Co₃₀Cr₁₀Fe₁₀Al₁₈W₂ alloy after heat treatment was also discussed.