Effect of gaseous silicon infiltration process on mechanical and ablation properties of C/C-HfC-SiC composites with HfSi₂/HfC coating prepared by reactive melt infiltration

Si element is considered to contribute to the enhancement of the ablation resistance of C/C-HfC-SiC composites. In this work, C/C-HfC-SiC composites with HfC-HfSi₂ ceramic layer formed in situ on the sample surface was fabricated by reactive melt infiltration (noted as NS). Si was introduced on the samples surface by gaseous silicon infiltration (noted as RS). The effect of the introduction of Si on the mechanical properties and ablative performance of the composites was investigated comparatively. Compared to NS, the value of flexural strength (141.4 ± 2.4 MPa) and flexural modulus (7.7 ± 1.9 GPa) of RS decreased by 23.65 % and 58.6 %, respectively. The mass and linear ablation rates after 40 s of ablation were 0.06 mg/s, −3.20 μm/s and 3.76 mg/s, −3.48 μm/s for NS and RS, respectively. Due to the introduction of Si, the mass ablation rate increases, while the linear ablation rate in the ablation center region remains almost invariant. The oxide film of transition zone is thinned with a linear ablation rate of 1.23 μm/s. In addition, the introduction of Si on the sample surface makes the thermal conductivity of RS lower than that of NS at low temperatures. When the Si on the sample surface is completely consumed, RS will demonstrate a higher thermal conductivity than NS owing to a larger grain size. Introducing low melting point phases such as Si can play an important role in ablation of the composites. This work provides a basis for the process improvement and performance enhancement of the composites.