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.
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