Effect of Ni and C additives on pressureless sintering and mechanical properties of ZrB2

High density bulk zirconium diboride was successfully produced by pressureless sintering with the Ni additive as sintering aid. Microstructure and phase formation were investigated by using scanning electron microscopy and X-ray diffractometry respectively. Microhardness, fracture toughness and compressive strength of the sintered samples were measured. Results showed that the higher Ni content led to higher densification, fracture toughness and hardness and lower compressive strength. A significant grain growth was observed during sintering at 2000°C, which may be due to the oxygen impurity in the surface of particles. The addition of 1 wt-%C led to oxygen removing and smaller grains after sintering.