Thermal properties and thermal shock resistance of liquid phase sintered ZrC-Mo cermets

The linear thermal expansion coefficient (CTE), heat capacity, and thermal conductivity, were investigated as a function of temperature for hot pressed ZrC and liquid phase sintered ZrC-Mo cermets. The ZrC and the ZrC-Mo cermets had the same CTE at 50 °C (∼5.1-5.5 ppm °C^-1), but the CTE of ZrC increased to ∼12.2 ppm °C^-1 at 1000 °C compared to ∼7.2-8.5 ppm °C^-1 for the ZrC-Mo cermets. Heat capacity was calculated using a rule of mixtures and previously reported thermodynamic data. Thermal diffusivity was measured with a laser flash method and was, in turn, used to calculate thermal conductivity. Thermal conductivity increased linearly with increasing temperature for all compositions and was affected by solid solution formation and carbon deficiency of the carbide phases. Hot pressed ZrC had the highest thermal conductivity (∼30-37 W m^-1 K^-1). The nominally 20 and 30 vol% Mo compositions of the ZrC-Mo cermets had a lower thermal conductivity, but the thermal conductivity generally increased with increasing Mo content. Water quench thermal shock testing showed that ZrC-30 vol% Mo had a critical temperature difference of 350 °C, which was ∼120 °C higher than ZrC. This increase was due to the increased toughness of the cermet compared to ZrC.