Preparation, microstructures, mechanical properties and oxidation resistance of SiBCN/ZrB₂-ZrN ceramics by reactive hot pressing

SiBCN/ZrB₂-ZrN ceramics were prepared by mechanical alloying followed by reactive hot pressing. The preparation, microstructures, mechanical properties and oxidation resistance were evaluated. Air exposure immediate before cooling leads to the formation of ZrB₂, ZrN, ZrO₂ and SiC. Reactive hot pressing provides composite materials with similar structures consisting of ZrB₂, ZrN, SiC and a BNC phase. The mechanical properties of the as-obtained ceramics depend on the volume fractions of the individual phases. High volume ratios of SiC/ZrB₂-ZrN in ceramics provide better oxidation resistance but reduce overall mechanical properties. The oxide surface of all investigated ceramics composes of SiO₂, ZrSiO₄ and ZrO₂ with a layered structure. The oxidation behavior of SiBCN/ZrB₂-ZrN ceramics in structure changes is similar, but the oxidation kinetics is different. The oxide layer can be divided into three layers: (1) outermost layer consists of SiO₂ glass with uniform distribution of ZrSiO_4, (2) porous ZrO₂-SiO₂ layer, (3) unreacted matrix.