Ablation resistance of supersonic-atmosphere-plasma-spraying ZrC coating doped with ZrO₂ for SiC-coated carbon/carbon composites

To improve the ablation resistance of ZrC coating for carbon/carbon (C/C) composites, the C/Zr ratio of the coating was changed by doping ZrO₂ using supersonic atmosphere plasma spraying (SAPS). The SAPS ZrC coating with 10 vol.% ZrO₂ showed a significant improvement on ablation resistance compared with SAPS ZrC coating without ZrO₂ and could protect C/C composites for more than 90 s at heat flux of 2.4 MW/m². The oxycarbides in the coating attenuated the destructiveness from gas products. The decreased C/Zr ratio and increased relative content of ZrC_xO_y in the multiphase coating reduced the CO evolution and contributed to the improvement on ablation resistance. An optimal oxycarbide was ZrC_x (0.61 < x < 1.0, y = 0) based on thermodynamic calculation. Excessive doping of ZrO₂ deteriorated the ablation resistance due to many potential oxygen penetration paths produced during heating and cooling and the probably increased vaporization of the coating.