Characterization 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.