Microstructures, mechanical properties and oxidation resistance of SiBCN ceramics with the addition of MgO, ZrO2 and SiO2 (MZS) as sintering additives

Abstract

Nano-crystalline SiBCN ceramics were prepared by mechanical alloying (MA) plus hot pressing (HP) with the addition of MZS1 (MgO, ZrO₂ and SiO₂) and MZS2 (ZrSiO₄ and SiO₂) as the sintering additives. The effects of the two additives on the microstructure, mechanical properties and oxidation resistance of SiBCN ceramics were carefully evaluated. The addition of MZS1 and MZS2 additives in the SiBCN matrix can boost elemental diffusion and matrix densification. Owing to the effective densification caused by the sintering additives, the mechanical properties of SM1 and SM2 samples are far superior to monolithic SiBCN. The oxide layers of SM1 and SM2 samples remain relatively dense and continuous, and have a strong binding capacity with the matrix after oxidation testing at 1500 °C for 20 h. The residual excess carbon in the SiBCN matrix should be responsible for the formation of ZrC and the outermost oxide layer structure is comprised of SiO₂ and ZrC after the oxidation test. The flexural strength, Young’s modulus, fracture toughness and Vicker’s hardness of the SM2 sample are much higher than monolithic SiBCN ceramics, reaching to 394.2 ± 41.7 MPa, 152.9 ± 16.0 GPa, 5.86 ± 0.86 MPa m^1/2 and 8.3 ± 0.6 GPa, respectively.