Physical and mechanical behaviours of hot-pressed TaC–HfC ceramics with La ₂ O ₃ additive

In this study, the compositions 4TaC-1HfC and 1TaC-1HfC ceramics were prepared via hot pressing 5 vol.-% La2O3-doped TaC-HfC powder mixtures in temperature range of 1700–2000°C. The effect of sintering temperature on the densification of the two compositions was assessed. Highly dense TaC-HfC ceramics were obtained after hot pressing at sintering temperature of 1750°C or greater, depending on the composition. The elastic properties, electrical conductivity, hardness, fracture toughness and flexural strength of the resulting highly dense ceramics were evaluated. The results show that the elastic properties, hardness and fracture toughness were insensitive to the composition, but the electrical conductivity and room temperature strength. On the other hand, the strength of the two compositions substantially degraded as the temperature increased from room temperature to 1000°C and the degradation depended on the composition. Subsequently, the strength gradually decreased with further increasing temperature up to 1400°C, but this decrease was insensitive to the composition.