Effect of different rare earth fluoride doping on microstructure and ablation properties of C/C–ZrC–SiC composites prepared by molten salt assisted reactive melt infiltration

The effect of doping with rare earth elements of different ionic radii on the ablation resistance of C/C–ZrC–SiC composites was investigated and the ablative behavior and ablation resistance of C/C–ZrC–SiC composites with the addition of different rare earth elements was tested. Although rare-earth doped stabilized zirconia has been used for a long time in the field of thermal barrier coatings, the existing techniques are usually coating modifications with rare-earth oxide or boride additions, it is difficult to prepare coatings that can be used on the surface of carbon matrix materials due to the large difference in the coefficients of thermal expansion. Therefore, this study attempts to introduce rare earth components into the interior of C/C–ZrC–SiC composites for matrix modification. The results show that the addition of rare earth elements enhances the ablation performance of the composites, but the mechanism of enhancement is different: rare earth ions with a smaller radius difference from Zr4+ ions stabilize the crystal structure of ZrO2 by forming replacement solid solutions and stabilize the surface oxide film structure by preventing the homogeneous multiphase transformation of the oxide to achieve higher ablation performance; whereas rare earth ions with a larger radius difference from Zr4+ ions cannot stabilize ZrO2 by replacement solid solutions, but instead form high viscosity, low volatility liquid phase oxides to heal the surface defects of the oxide film and reduce liquid phase dissipation to enhance ablation performance.