Abstract
Ultra-high temperature ceramic matrix composites adopt a multicomponent matrix to increase stability in a wide temperature range. However, oxides with lower melting points evaporated rapidly under prolonged high heat flux erosion, leaving refractory metal oxides with residual porosity, which restricted the lifetime of the composites. This study prepared LaB6-modified C/HfC-SiC composites through slurry-assisted polymer infiltration and pyrolysis method to improve ablation resistance and reusability, the influence of different LaB6 contents on the ablation resistance and mechanism of composites were investigated. Results indicated HfC, SiC, and La were uniformly dispersed within the fiber bundles and matrix, the density and flexural strength of the composites doped 5 mol% LaB6 were 3.78 g/cm3 and 323 MPa, respectively. The oxide layer remained intact after ablation for 240 s, due to the molten La2Hf2O7 and La2Si2O7 with high melting-point and viscosity filled the crack in the HfO2 framework, which were formed by the reaction of La between SiO2 and HfO2. The linear and mass ablation rates of the composites with 5 mol% LaB6 were 4.75×10− 3 mm/s and 1.39×10− 3 g/s, respectively.