Mechanical properties and thermal shock behavior of hot-pressed ZrB₂-SiC-AlN composites

ZrB₂-based ceramics containing 20 vol.% SiC and 10 vol.% AlN were prepared by hot pressing two different ZrB₂ precursor powders with average particle sizes of 5 μm in ZSA (ZrB₂-20 vol.% SiC-10 vol.% AlN) and 2 μm in GZSA (ZrB₂-20 vol.% SiC-10 vol.% AlN) ceramics. The microstructures and mechanical properties were investigated. The thermal shock behavior was studied through the methods of retained flexural strength after quenching into water of 20 °C with the temperature differences between 0 and 800 °C. GZSA showed a better resistance to thermal shock in terms of the increased critical temperature difference (ΔT_C of GZSA was 408 °C, about 40 °C higher than that of ZSA), since the finer grain size enhanced fracture toughness by promoting crack bridging, which inhibited the propagation of cracks due to thermal stresses. The influence of quenching temperature difference on the fracture toughness was not significant. Comparing with ZSA, the thermal stress fracture resistance parameter, R, and thermal stress damage resistance parameter, R″″, of GZSA were all increased.