Characterisation and High Temperature Mechanical Properties of Zirconium Boride-Based Materials

Two different ZrB2-based materials were produced by hot pressing: pure ZrB2 and ZrB2+4wt.% Ni. The relative densities of the two materials were 86.5 and 98.0%, respectively. Several physical and mechanical properties were measured in ambient air. From these data it appears that the porosity of 13.5% of pure ZrB2 strongly affects the properties. However at high temperature the presence of Ni-rich phases dominates the fracture behaviour and is responsible for the dramatic strength degradation (especially at 1200 °C). The high temperature creep was evaluated by uniaxial compression tests. Samples of both materials were deformed in argon atmosphere at temperatures between 1400 and 1600 °C and at stresses ranging between 47.0 and 472.3 MPa (pure ZrB2) and 10 63.5 MPa (Ni-doped ZrB2). Pure ZrB2 showed a ductile behaviour under these conditions. On the other hand, Ni-doped ZrB2 failed catastrophically for stresses higher than 25 MPa, approximately, at relatively low strains, showing a ductile behaviour only at lower stresses. This behaviour may be related to the presence of Ni-rich grain boundary phases at triple points of the grain structure.