Preparation of Si₃N₄–TiN–SiC composite by partial substitution of Ti–Si–Fe alloy for Si under N₂ atmosphere

Si₃N₄–TiN–SiC composites were prepared by partial substitution of the Ti–Si–Fe alloy extracted from high-titanium blast furnace slag for Si under nitrogen atmosphere. The nitridation, microstructure and mechanical properties of the composites were investigated in detail. The results show that Ti–Si–Fe alloy facilitated the nitridation of Si and full nitridation of Si was achieved in the compacts with 3.6–5.4 wt.% Ti–Si–Fe alloy additive, and thus, densification and mechanical performances of the composites were improved obviously. Propagating of microcracks induced by the volume expansions accompanying with the conversion of Ti₅Si₃ and TiSi₂ to nitrides at 950–1050 °C built new N₂(g) transport channels in the compacts. In the following up nitridation process, adequate N₂(g) was transported through these channels into the compacts to fundamentally enhance contact of N₂ with Si, facilitate and ensure the complete nitridation of internal Si. Moreover, the Ti–Si–Fe–Mn–N eutectic liquid played an important role in the formation of both α- and β-Si₃N₄, and the Fe in the Ti–Si–Fe alloy was of great importance for the formation of fibrous Si₃N₄ by the reaction between SiO(g) and N₂(g).