Effects of LaB6 on the ablation properties and mechanism of C/HfC-SiC composites

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.