Effects of the La₂O₃ addition contents on the ablation performance of in-situ La-doped ZrC-SiC-ZrSi₂ coating for C/C-ZrC-SiC composites

The C/C-ZrC-SiC composites coated by the La-doped ZrC-SiC-ZrSi₂ coatings containing different La contents were fabricated by reactive melt infiltration (RMI) combined with gradient pack cementation in a one-step process. The composites' ablation behaviors under the oxyacetylene flame were comparatively studied. The effects of the La₂O₃ addition contents on the microstructure and phase composition evolution on the surface of the composites caused by ablation were investigated. The results indicated that the C/C-ZrC-SiC composites with an in-situ La-doped ZrC-SiC-ZrSi₂ coating prepared by the mixed powders with 15 wt% La₂O₃ (15LZS) showed a better ablation performance. After ablation for 120 s, their mass and linear ablation rates were − 0.62 ± 0.15 mg/s and − 2.42 ± 0.24 μm/s, respectively. Such good ablation resistance should owe to appropriate La contents on the surface of the 15LZS. During ablation, the La elements could promote the formation of a dense oxide layer, which was composed of the m-ZrO₂, t-ZrO₂, and Zr_0.9La_0.1O_1.95 phases. It could efficiently inhibit oxygen diffusion and endure the mechanical denudation of the oxyacetylene flame.