Thermal shock characterization of large size ZrB₂ ceramic matrix composite material

Ultra high temperature ceramic (UHTC) contained aluminium nitride (A1N) was fabricated at 1950°C for 1 h under a uniaxial load 40MPa by hot pressing. The mechanical properties and thermal shock behavior were investigated. It was shown that three-point residual bending strength was 612.4MPa, and the fracture toughness was 5.91 MPa/m^1/2 at room temperature. Residual bending strength with quenching temperatures was tested in three-point bending on 3mm×4mm×36mm bars. The results presented that residual strength decreased abruptly at the quenching temperature of 1200°C, and increased subsequently. It can be observed from SEM that surface damage appeared at the quenching temperature of 1200°C, and no damage appeared at the quenching temperature of 1450°C which may be attributed to thicker glass phase layer created at this temperature. Finally, upper limit of coefficient of surface heat transfer for boiling water was evaluated by finite element method, and it was evaluated for surface stress of the specimens quenched in boiling water.