Novel MoSi₂-modified HfB₂-SiC composites fabricated by reactive melt infiltration：Microstructure and long-term oxidation resistance at 1650°C

HfB₂-SiC-MoSi₂ composites with varying MoSi₂ contents were fabricated via gel-casting molding combined with reactive melt infiltration (RMI) at a relatively low temperature of 1500℃, achieving high density with porosity less than 1 % and uniformly distributed constituent phases. The composites exhibited excellent oxidation resistance during isothermal oxidation at 1650 °C, with mass gains of 15.40, 8.50, 7.38, and 11.31 mg/cm² after 100 h. The oxide layer grew thicker and tended to be uniform and dense over time. The oxidation process all followed a parabolic law. The addition of MoSi₂ significantly reduced the oxidation rate. The mechanism is attributed to the fact that the oxidation of MoSi₂ can promote the formation of additional SiO₂ glass, facilitating the rapid development of a dense protective oxide layer, thereby effectively blocking oxygen diffusion and suppressing the formation of a SiC-depleted layer. An appropriate amount of MoSi₂, specifically 20 wt% MoSi₂, optimizes the fluidity of the glass layer and enhances pore filling; however, excessive MoSi₂ reduces HfO₂ content and weaken viscosity. The formation of the HfSiO₄ phase with high-melting-point further improves the structural stability and oxygen resistance of the oxide scale, extending the service life at 1650°C. This work provides valuable guidance for designing oxidation-resistant materials for prolonged aerospace applications.