Mechanical behavior of zirconium diboride-silicon carbide ceramics at elevated temperature in air

The mechanical properties of zirconium diboride-silicon carbide (ZrB2-SiC) ceramics were characterized from room temperature up to 1600 °C in air. ZrB2 containing nominally 30 vol% SiC was hot pressed to full density at 1950 °C using B4C as a sintering aid. After hot pressing, the composition was determined to be 68.5 vol% ZrB2, 29.5 vol% SiC, and 2.0 vol% B4C using image analysis. The average ZrB2 grain size was 1.9 μm. The average SiC particles size was 1.2 μm, but the SiC particles formed larger clusters. The room temperature flexural strength was 680 MPa and strength increased to 750 MPa at 800 °C. Strength decreased to ∼360 MPa at 1500 °C and 1600 °C. The elastic modulus at room temperature was 510 GPa. Modulus decreased nearly linearly with temperature to 210 GPa at 1500 °C, with a more rapid decrease to 110 GPa at 1600 °C. The fracture toughness was 3.6 MPa·m½ at room temperature, increased to 4.8 MPa·m½ at 800 °C, and then decreased linearly to 3.3 MPa·m½ at 1600 °C. The strength was controlled by the SiC cluster size up to 1000 °C, and oxidation damage above 1200 °C.