Two‐step synthesis process for high‐entropy diboride powders

Abstract High‐entropy diboride powders were produced by a two‐step synthesis process consisting of boro/carbothermal reduction followed by solid solution formation. Nominally phase‐pure (Hf,Zr,Ti,Ta,Nb)B 2 in a single‐phase hexagonal structure had an average particle size of just over 400 nm and contained 0.3 wt% carbon and 0.3 wt% oxygen. The fine particle size was due to the use of high‐energy ball milling prior to boro/carbothermal reduction, which led to a relatively low synthesis temperature of 1650°C. Oxygen and carbon contents were minimized by completion of the boro/carbothermal reduction reactions under vacuum. This is the first report of synthesis of a nominally phase pure high‐entropy diboride powder from oxides using a two‐step process.