Thermal and electrical properties of spark plasma sintered (Ti,Cr)B2 ceramics

Thermal and electrical properties were measured for TiB₂ ceramics containing varying CrB₂ contents up to 33 mol%. The room-temperature thermal diffusivity decreased with increasing Cr content from 0.330 ± 0.003 cm²/s for pure TiB₂ to 0.060 ± 0.003 cm²/s for (Ti_0.66Cr_0.33)B₂. The amount of anisotropy in the coefficients of thermal expansion increased with increasing Cr content and the c-axis had the greatest dependence on Cr addition, with an increase of more than 25% in the thermal expansion for 33 mol% CrB₂ compared to TiB₂, whereas the a-axis only increased by about 8%. The electrical conductivity was the lowest for (Ti_0.66Cr_0.33)B₂ at ∼8.5 × 10³ S/cm compared to ∼106.1 × 10³ S/cm for nominally pure TiB₂. Overall, the addition of CrB₂ as a sintering aid for TiB₂ was shown to have a significant effect on the thermal and electrical properties of TiB₂ for additions as small as 5 mol% CrB₂.     

Pressureless sintering of dual-phase,high-entropy boride–carbide ceramics

Dual-phase, high-entropy boride–carbide ceramics were densified by pressureless sintering. Relative densities up to approximately 96% were obtained for ceramics containing about 30 vol% high-entropy boride and 70 vol% high-entropy carbide. Isostatic pressing at 200 MPa resulted in higher relative densities of both the green bodies and final ceramics compared to uniaxial pressing. The highest relative density of 96.3% was achieved for a ceramic that was isostatically pressed at 200 MPa and sintered at 2300°C for 2 h. Grain sizes of the resulting ceramics were approximately 2 µm. This is the first report of pressureless sintering of dual-phase, high-entropy boride–carbide ceramics.