Single-stage reaction hot pressing route for dense refractory high entropy TiZrHfVNbTaB12-C ceramic composite

Hot pressing reaction-assisted sintering of novel refractory ceramic composite TiZrHfVNbTaB12-C was undertaken. The sintered material belongs to the class of Ultra-High-Temperature Ceramics (UHTCs). The sintering was done by utilizing transitional metal carbides and B4C at 1950 °С and 30 MPa for 8 min in a graphite die within an argon atmosphere. The ceramic demonstrated 98% density as measured by Archimedes’ method with accounted ceramic contamination by ZrO2 during initial carbide milling. X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) revealed a single multimetal boride phase with AlB2-type (hexagonal, P6/mmm) structure and carbon inclusions. It is thought that the high concentrations of transitional metals lead to high configurational entropy effects and this produces a single boride phase. On those grounds, the ceramic belongs to the class of High Entropy Ceramics (HECs). The composite Vickers’ hardness HV was 12 ± 1 GPa and indentation toughness K1C was 4.3 ± 0.3 MPa·m1/2.