Thermal Shock Resistance and Fracture Behavior of ZrB2-Based Fibrous Monolith Ceramics

The thermal shock resistance and fracture behavior of zirconium diboride (ZrB2)-based fibrous monoliths (FM) were studied. FMs containing cells of ZrB2-30 vol% SiC with cell boundaries composed of graphite-15 vol% ZrB2 were hot pressed at 1900 degrees C. The average flexure strength of the FMs was 375 MPa, less than half of the strength of hot-pressed ZrB2-30 vol% SiC. Flexure specimens failed noncatastrophically and retained 50%-85% of their original strength after the first fracture event. A critical thermal shock temperature (Delta T-c) of 1400 degrees C was measured by water quench thermal shock testing, a 250% improvement over the previously reported Delta T-c values for ZrB2 and ZrB2-30 vol% SiC of similar dimensions (4 mm x 3 mm x 45 mm). The flexure strength was maintained with Delta T-c values of 1350 degrees C and below. As Delta T-c increased, the stiffness of the flexure specimen decreased linearly. The lower stiffness and improvement in thermal shock resistance is attributed to crack propagation in the cell boundary and crack deflection around the load-bearing cells. The critical thermal shock was attributed to the fracture of the ZrB2-30% SiC cell material.