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 L1(2) gamma 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 gamma solvus are above 1150 degrees C, and the gamma-gamma microstructure can be thermodynamically stable after isothermal ageing from 700 to 1100 degrees C for at least 500 h. By XRD peak deconvolution, positive lattice misfits between g and gamma have been shown till elevated temperatures. The results from nano-indentation test indicate that their highly alloyed gamma 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.