Thermal properties of field‐assisted‐sintered SiCN–Y2O3 composites.

Polymer‐derived amorphous SiCN has excellent high‐temperature stability and properties. To reduce the shrinkage during pyrolysis and to improve the high‐temperature oxidation resistance, Y2O3 was added as a filler. In this study, polymer‐derived SiCN–Y2O3 composites were fabricated by mixing a polymeric precursor of SiCN with Y2O3 submicron powders in different ratios. The mixtures were cross‐linked and pyrolyzed in argon. SiCN–Y2O3 composites were processed using field‐assisted sintering technology at 1350°C for 5 min under vacuum. Dense SiCN–Y2O3 composite pellets were successfully made with relative density higher than 98% and homogeneous microstructure. Due to low temperature and short time of the heat‐treatment, the grain growth of Y2O3 was substantially inhibited. The Y2O3 grain size was ∼1 μm after sintering. The composites' heat capacity, thermal diffusivity, and thermal expansion coefficients were characterized as a function of temperature. The thermal conductivity of the composites ceramics decreased as the amount of amorphous SiCN increased and the coefficient of thermal expansion (CTE) of the composites increased with Y2O3 content. However, the thermal conductivity and CTE did not follow the rule of mixture. This is likely due to the partial oxidation of SiCN and the resultant impurity phases such as Y2SiO5, Y2Si2O7, and Y4.67(SiO4)3O. [ABSTRACT FROM AUTHOR]