Densification, mechanical and thermal properties of ZrC1 − x ceramics fabricated by two-step reactive hot pressing of ZrC and ZrH2 powders

Densification behavior, mechanical and thermal properties of ZrC1 − x ceramics with various C/Zr ratios of 0.6-1.0 have been investigated by two-step reactive hot pressing of ZrC and ZrH2 powders at 30 MPa and 1500-2100 °C. The two-step reactive hot pressed ZrC1 − x ceramic has a higher relative density (> 95.3%) than that (91.9%) of stoichiometric ZrC sintered at 2100 °C. A cubic Zr2C-type ordered phase forms in the ZrC1 − x sample obtained at a ZrC/ZrH2 molar ratio of 0.6 at a relatively low temperature of 1100 °C. The decrease in C/Zr ratio is beneficial to densification of ZrC1 − x ceramic, however, excess grain growth occurs after sintering above densification temperature. The elastic modulus and Vickers hardness decrease with decreasing the C/Zr ratio. With decreasing the C/Zr ratio, both thermal conductivity and specific heat decrease due to the enhanced scattering of conducting phonons and electrons by carbon vacancies.