Abstract: An Al-AlN core-shell structure is beneficial to the performance of Al-Al₂O₃ composites. In this paper, the phase evolution and microstructure of Al-Al₂O₃-TiO₂ composites at high temperatures in flowing N₂ were investigated after the Al-AlN core-shell structure was created at 853 K for 8 h. The results show that TiO₂ can convert Al into Al₃Ti (~1685 K), which reduces the content of metal Al and rearranges the structure of the composite. Under N₂ conditions, Al₃Ti is further transformed into a novelty non-oxide phase, TiCN. The transformation process can be expressed as follows:Al₃Ti reacts with C and other carbides (Al₄C₃ and Al₄O₄C) to form TiC_x (x < 1). As the firing temperature increases, Al₃Ti transforms into a liquid phase and produces Ti(g) and TiO(g). Finally, Ti(g) and TiO(g) are nitrided and solid-dissolved into the TiC_x crystals to form a TiCN solid solution.