Theoretical and experimental investigations on the phase stability and fabrication of high-entropy monoborides

To obtain thermodynamically stable single-phase high-entropy monoborides (HEMBs), the formation abilities of two-compound monoborides were evaluated in advance by first principles calculations, which were constructed from two cation combinations chosen from 11 transition metals including Ti, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, and Ni. And this method was extended to HEMBs on predicting the relative feasibility of synthesis and the tendency of phase segregation from the mean mixing enthalpy (mu local) and the standard deviation (sigma local). Results showed that the contribution of entropy to free energy for entropy-stable HEMBs is large, and HEMBs with small sigma local are easy to obtain the higher single-phase formation ability. In addition, four HEMBs ceramic with Vickers hardness (41-45 GPa) were synthesized as superhard materials. This work provides a realistic theoretical guidance for the design and performance research of HEMBs, and will effectively promote the application of superhard HEMBs ceramics.