Influence of Si-based alloys on BN-SiC interphase stability during SiC/SiC composite production by liquid silicon infiltration

Alloying silicon is a promising strategy to control thermochemical interactions during the production of silicon carbide fiber-reinforced silicon carbide composites by liquid silicon infiltration, yet its influence on fiber-matrix interphases remains insufficiently understood. In this study, five Si-based systems (Si, Si-B, Si-Zr, Si-Hf, Si-Mo) were systematically compared by combining differential scanning calorimetry with infiltration experiments on composites containing BN-SiC interphases. Melting temperatures and enthalpies as well as reaction temperatures and enthalpies were quantified and correlated with interphase integrity. The results show that interphase survival cannot be predicted from thermal properties alone. Instead, stability is governed by the interplay of thermochemical and interfacial effects. Si-B and Si-Zr preserve the interphase through stabilization of the SiC microstructure and formation of protective interfacial layers, respectively, whereas Si-Hf and Si-Mo cause pronounced degradation. These findings establish alloy chemistry as a key parameter for damage-tolerant SiC/SiC composites processed by liquid silicon infiltration.