Friction and Wear Test of Titanium Boride Ceramics at Elevated Temperatures

Sliding friction and wear tests of sintered titanium boride were conducted in air from room temperature to 1000°C. At room temperature, the coefficient of friction was about 0.8 independent of both the applied load and the sliding speed. It increased at intermediate temperatures around 400°C, particularly at lower applied loads. The wear loss decreased with increasing temperature up to 600°C. The coefficient of friction abruptly decreased at 600°C and exhibited a minimum value of about 0.3 at 800°C. A weight gain was observed after the tests at 800°C and above. X-ray diffraction analysis of the wear surfaces revealed that titanium boride oxidizes even at lower temperatures. Since the oxidation yields B2O3 of low melting point, it would exist as a liquid at the friction interfaces and therefore should have a critical effect on the friction and wear characteristics. High viscosity of liquidized oxides increased the coefficient of friction but decreased the wear loss at intermediate temperatures. The dependence of friction coefficient on both the applied load and the sliding speed suggests that the sliding is in a hydrodynamic lubrication regime because of the presence of a substantial amount of melted oxides at 800°C and above, resulting in a low coefficient of friction.