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.

Automated summary

ZrB2 was mixed with 0.5 wt% carbon and up to 10 vol% ZrC and densified by hot-pressing at 2000 degrees C. The resulting dense ceramics exhibited reduced ZrC content and residual carbon, smaller ZrB2 grain sizes, larger ZrC cluster sizes, increased elastic modulus, hardness, toughness, and flexure strength with increasing ZrC content. The strength-limiting flaw was identified as ZrB2 grain pullout.