Formation mechanism of γ-AlON and β-SiC reinforcements in a phenolic resin-bonded Al–Si–Al₂O₃ composite at 1700 °C in flowing N₂

An AlON–SiC–Al₂O₃ composite was successfully prepared by sintering the phenolic resin-bonded Al–Si–Al₂O₃ green body at 1700 °C in flowing nitrogen. The results show that the major phases of the samples after sintering are α-Al₂O₃, γ-AlON, and β-SiC. The reaction mechanism is as follows: At high temperatures, the phenolic resin is pyrolyzed to produce nanoscale, highly reactive residual carbon, which greatly reduced the stability of α-Al₂O₃ fine particles and also improves the wettability of Al(l) to α-Al₂O₃. After a good physical contact between Al(l) and α-Al₂O₃ is achieved, octahedral γ-AlON is formed by the aluminum thermal nitridation of α-Al₂O₃ fine particles at 1700 °C [\( {\text{Al}}({\text{l}}) + {\text{C}}({\text{s}},{\text{resin}}) + {\text{Al}}_{2} {\text{O}}_{3} ({\text{s}}) + {\text{N}}_{2} ({\text{g}}) \to {\text{Al}}_{5} {\text{O}}_{6} {\text{N}}({\text{s}}) + {\text{CO}}({\text{g}}) \)]. Then, the CO(g) released by the reaction is rapidly absorbed by the Si(l) in the system to form stable β-SiC phase, resulting in a decrease in P_CO, which further promotes the formation and stability of γ-AlON. The Al₂O(g) and Al(g) are the major gas phases in the system at 1700 °C, which further participated in the reaction of γ-AlON formation and makes γ-AlON grow in a step growth method. The γ-AlON and β-SiC stably coexist as reinforcing phases in the samples, forming an AlON-SiC-Al₂O₃ composite, which has a high cold crushing strength of 389–443 MPa. The reaction model is established.