Synthesis of high entropy monoboride (Mo_0.25W_0.25Cr_0.25Ta_0.25)B powders with abundant twins from oxides

High entropy monoborides powders are mainly prepared from metal and boron powders which can be costly. In this study, a novel approach starting from mixed oxides, boron carbide, and graphite was first developed to synthesize quaternary monoboride powders by combining multiple boro/carbothermal reductions (MBCTR). As an exemplar, (Mo0.25W0.25Cr0.25Ta0.25)B powders with purity up to 94.3 wt.% were successfully synthesized by heating the mixtures in vacuum at 1650 degrees C for three times, as-synthesized powders exhibit fine particle size (<1 mu m) and uniform elemental distribution. MBCTR not only increased the purity of monoborides but resulted in abundant twins and stacking faults in the final powders. This work has proposed a new and low-cost strategy of synthesizing high-purity and fine monoboride powders.