Mechanical property, oxidation resistance, and ceramization mechanism of MoSi2-SiB6 reinforced phenolic resin matrix composites

Ceramizable phenolic resin matrix composites have a significant potential for widespread applications in the field of aerospace ablation. However, due to the sharp decrease of mechanical properties at elevated temperatures, the composite fails to meet the requirements of thermal protection as well as load-bearing of aircraft in a wide temperature range. In this study, boron phenolic composites modified by MoSi2 and SiB6 with high strength in a wide temperature range are prepared. The flexural strength of composites after ablation within the temperature range of 800 °C to 1600 °C ranges from 48.07 to 82.49 MPa. In particular, a significant increase of 224.9% is obtained at 1400 °C with 6 wt% SiB6. The mass ablation rate and line ablation rate of the composites are increased to 0.054 g/s and 0.013 mm/s, respectively. The cooperation effect of oxygen consumption, carbon fixation, oxygen barrier, and liquid phase bonding produced by ceramization reactions involving SiB6, MoSi2, O2, and pyrolytic carbon at different temperatures, resulting in an improvement of the mechanical property and the oxidation resistance of the composite. These composites have a potential in long term thermal protection and load-bearing of new ablation materials.