Toughening mechanism and oxidation resistance of SiC whisker-toughened SiAlCN ceramics

Mechanical alloying and spark plasma sintering were used to prepare dense SiC_w/SiAlCN ceramics. The effects of whisker content on the mechanical properties and oxidation resistance were investigated. Compared with SiAlCN ceramic, the fracture toughness of 5 wt% SiC_w/SiAlCN ceramic increased by 31.8 % to 5.8 MPa m^1/2, which was attributed to crack deflection/branch and SiC_w bridging/pull-out. Based on quantitative calculation, SiC_w bridging/pull-out increased fracture toughness by 27.8 %. The flexural strength of 5 wt% SiC_w/SiAlCN ceramic was 523.2 MPa, which was 26.9 % higher than that of SiAlCN ceramic. The residual strengths of the SiC_w/SiAlCN ceramic after 50 h isothermal oxidation at 1500 °C and 50 times thermal cycles from room temperature to 1500 °C were 292.5 and 449.7 MPa. Because of SiAlCN matrix passive oxidation and SiC_w active oxidation, a double-layer oxide scale composed of glassy scale and porous scale was formed on SiC_w/SiAlCN ceramics. The unoxidized whiskers could remain original morphology and were available to strengthening and toughening.