Microstructure, mechanical properties, and oxidation behavior of hot-pressed ZrB₂–SiC–B₄C composites

The microstructure, mechanical properties, and oxidation behavior of a ZrB₂–20 vol% SiC–5 vol% B₄C composite hot-pressed at the temperature of 1850 °C for 1 h under 40 MPa were investigated. A highly dense ceramic with a density of 99.4% containing ZrB₂, SiC, and B₄C phases in the final sintered sample, was obtained. The fractography revealed the existence of few oxide impurities in cauliflower-like morphologies. The mechanical properties investigations showed that the composite possessed a Vickers hardness of 20.1± 1.2 GPa, a flexural strength of 275 ± 21 MPa, and a fracture toughness of 4.0 ± 0.2 MPa m^1/2. An oxidation activation energy of 275.2 kJ/mol was estimated by studying the behavior of the oxidation process at the temperatures of 1000, 1400, and 1700 °C for 1, 4, and 10 h. Moreover, different layers formed during the specimen's oxidation process: a ZrO₂/SiO₂/B₂O₃ layer, a ZrB₂/SiC–depleted intermediate layer, and an unaffected substrate. It was found that the released carbon monoxide has the tendency to move toward the outer oxidized layer in order to leave the bulk structure.