The ablation behaviors of ZrB2-based UHTC coating with La2O3-modified SiC bond coat

Ultra-high temperature ceramic (UHTC) has been developed to protect C/C composites exposed to hightemperature oxidizing environment. In this study, the effect of additive for the ablation behavior of ZrB2based coating was investigated. The SiC-La2O3 bond coat was firstly prepared on the C/C composites by the method of pack cementation (PC). ZrB2-SiC-Si (ZSS) and ZrB2-SiC-Al2O3 (ZSA) coatings with dense microstructure and excellent interfacial bonding then were prepared on the surface of C/C composites coated with SiC-La2O3 layer by the method of atmospheric plasma spraying (APS). The ablation experiments of all coated samples were conducted under oxyacetylene torch with a heat flux of 4.18 MW/m2. The microstructure, phase compositions, interfacial bonding, ablation and oxidation behaviors of coating were investigated. After ablation test, the ZrO2 sketon with prorous structure was formed in the central region of ZSS coating. However, denser structure still can be observed at ZSA coating due to the formation of liquid phase. The SiC-La2O3-C/C interface are still without cracks. Furthermore, the diffusion of La element into ZSS and ZSA coatings from the SiC-La2O3 layer was beneficial for the improvement of ablation resistance. The result indicated that SiC-La2O3/ZSA could effectively provide protection for C/C composites.