Effect of the transition metal segregation on the properties of (Hf,Ti,Zr)B2–(Hf,Ti,Zr)C Dual Phase Ceramics

Abstract

Dual phase mid entropy ceramics are attractive due to potential synergistic effects of the constituents on mechanical properties and thermal stability. The co-synthesis method was used to obtain boride and carbide constituents by boro/carbothermal reduction of mixtures of oxides and appropriate amounts of carbon black and B4C. Solid solution formation and densification of the reacted powders were done at 1900 °C or 1950 °C utilizing two-step spark plasma sintering. Chemical compositions were measured using energy dispersive spectroscopy. Based on the transition metal distribution in the dual phase ceramic, individual mid entropy boride and carbide ceramics were produced using the same conditions. The final microstructures had submicron grains due to the pinning effect of the two phases, while grain sizes of the individual mid entropy carbides and borides were higher than the two-phase ceramics. Vickers hardness values for dual phase ceramics were higher than values calculated using a volumetric rule mixtures from individual components. Thermal and electrical properties were also higher values than calculated using volumetric rule mixtures of individual components. Thermal conductivity of the optimized dual phase ceramic produced at 1950 °C displayed an increase of ~15% compared to the constituent phases.