Thermal Shock Resistance of ZrB2 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 19001C. 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 (DTc) of 14001C was measured by water quench thermal shock testing, a 250% improvement over the previously reported DTc values for ZrB2 and ZrB2–30 vol% SiC of similar dimensions (4 mm3 mm45 mm). The flexure strength was maintained with DTc values of 13501C and below. As DTc 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.


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