A ZrC-SiC/ZrC-LaB₆/ZrC multilayer ablation resistance coating for SiC-coated carbon/carbon composites

This work proposes a new multilayer coating system containing ZrC-SiC, ZrC-LaB₆, ZrC layer with respectively different functions to protect the carbon/carbon (C/C) composites. The coating system overcame the poor oxidation resistance of ZrC coating and weak anti-scouring performance of modified ZrC coating, which could provide the protection for C/C composites through the whole ablation process. After ablation for 40 s, the liner ablation rate of the multilayer coating was − 2.89 ± 0.23 μm/s, decreased by 150.26%, 134.61% and 133.22% relative to the ZrC, ZrC-LaB₆ and ZrC-SiC coating, respectively. The coating showed a weight gain, while all the other coatings lost weight after ablation. The good ablation resistance was mainly ascribed to different functions of these layers in the coating system. The ZrC-SiC layer provided oxidation protection during the initial ablation stage by forming a composite oxide of ZrO₂-SiO₂. In the intermediate stage, the ZrC-LaB₆ layer promoted the formation of a stable scale containing (La_0.1Zr_0.9)O_1.95. As the ablation going on, a compact scale containing (La_0.1Zr_0.9)O_1.95 and La₂Zr₂O₇ was formed, which further protected the composites. During ablation, the ZrC layer provided a foundation for the multilayer coating system against scouring.