On The Superior High Temperature Hardness of Precipitation Strengthened High Entropy Ni-Based Alloys

The microstructure and high temperature hardness of two face-centered cubic high entropy Ni-based alloys with L1₂ γ′ precipitates have been studied. Both alloys exhibit higher mixing entropy and with the advantages in lower density and lower cost of raw materials than conventional Ni-based superalloys. Their γ′ solvus are above 1 150 °C, and the γ–γ′ microstructure can be thermodynamically stable after isothermal ageing from 700 to 1 100 °C for at least 500 h. By XRD peak deconvolution, positive lattice misfits between γ and γ′ have been shown till elevated temperatures. The results from nano-indentation test indicate that their highly alloyed γ′ phase have rendered more significant strengthening, and the underlying mechanism can be attributed to the higher anti-phase boundary energy. Therefore, with minor refractory additions, the bulk hardness of present alloys can surpass that of commercial superalloy from room to high temperature.