Processing and mechanical properties of hot-pressed zirconium diboride - zirconium carbide ceramics

ZrB2 was mixed with 0.5 wt% carbon and up to 10 vol% ZrC and densified by hot-pressing at 2000 degrees C. All compositions were > 99.8% dense following hot-pressing. The dense ceramics contained 1-1.5 vol% less ZrC than the nominal ZrC addition and had between 0.5 and 1 vol% residual carbon. Grain sizes for the ZrB2 phase decreased from 10.1 mu m for 2.5 vol% ZrC to 4.2 mu m for 10 vol% ZrC, while the ZrC cluster size increased from 1.3 mu m to 2.2 mu m over the same composition range. Elastic modulus was similar to 505 GPa and toughness was similar to 2.6 MPa.m(1/2) for all compositions. Vickers hardness increased from 14.1 to 15.3 GPa as ZrC increased from 2.5 to 10 vol%. Flexure strength increased from 395 MPa for 2.5 vol% ZrC to 615 MPa for 10 vol% ZrC. Griffith-type analysis suggests ZrB2 grain pullout from machining as the strength limiting flaw for all compositions.