Synthesis, microstructure and mechanical properties of ZrB₂ ceramic prepared by mechanical alloying and spark plasma sintering

Dense bulk ZrB₂ ceramic was synthesized by mechanical alloying (MA) and followed spark plasma sintering (SPS) using zirconium and boron as initial materials. It was found that MA process was effective to fragment the coarse metal zirconium particles from 45 μm to less than 1 ?m within 20 hours. In comparison with the commercial ZrB₂ powder, the as-obtained zirconium and boron mixture powders showed higher sinterability. When the sintering was carried out at 1800°C, the relative density of synthesized ZrB₂ samples using mixture powder was above 95%, higher than that of ZrB₂ sample prepared using commercial powder (73%). Vickers hardness of those ZrB₂ samples was at the same level of 15 GPa. However, the fracture toughness of ZrB₂ samples seemed to depend on the heating rate of the SPS process. Corresponding to the heating rates of 10, 50, and 100°C/min, the fracture toughness of as-prepared ZrB₂ samples were 3.83, 3.19, and 2.74 MPa·m^1/2, respectively.