Effect of yttrium carbide on ablation behavior of zirconium carbide modified carbon/carbon composites

•The chemical reactions between carbon, ZrC, and YC2 and the oxidizing species were studied based on the principle of minimum free energy.•Oxygen vacancies produced by Y2O3 doped ZrO2 provide passages for the oxidizing species, accelerating the thermal chemical reactions.•The produced oxides (ZrO2 and Y2O3) react violently with carbon causing the formation of a large number of pits on the carbon fibers and matrices.•Pits provide active sites, accelerating the chemical ablation, and reduce the strength of fibers/matrix, increasing the mechanical breakage.•Ablation of C/C-ZrC-YC2 is controlled by the chemical ablation and mechanical breakage, while that of C/C-ZrC mainly depends on the chemical ablation.