Densification, microstructure, elastic and mechanical properties of reactive hot-pressed ZrB2-ZrC-Zr cermets

In this study, cermets composed of zirconium diboride and zirconium carbide with intergranular zirconium were sintered by reactive hot-pressing. Relative density exceeding 97% was obtained for the sintered cermets having four distinct compositions varying in concentration of excess Zr. Their densification behaviour was examined by monitoring displacement during sintering. The microstructure was characterized by scanning electron microscopy and X-ray diffraction, and the elastic and mechanical properties were evaluated at room temperature. The effects of Zr concentration on the densification and mechanical properties were assessed. The ZrB2 and ZrC micron-grains coarsened with increasing amount of Zr starting material. In addition, the cermets exhibited high flexural strength (546-890 MPa) and fracture toughness (6.63-10.24 MPa m1/2), which simultaneously increased with increasing Zr concentration. However, the elastic moduli and hardness (11-18 GPa) decreased with increasing Zr. The shear modulus and Young's modulus were in the range of 150-190 GPa and 360-440 GPa, respectively.