Sliding wear behavior and tribofilm formation of ceramics at high temperatures

Sliding friction and wear tests were performed for four sintered ceramics including mullite, alumina, silicon carbide and titanium diboride (TiB2), in various combinations at room temperature, 500 and 1000 °C in air. The coefficient of friction of the ceramics was nearly constant regardless of sliding combinations and test temperatures. The specific wear rates at room temperature and 500 °C were high, usually of the order of 10−4 mm3/Nm, whereas low wear rates of the order of 10−5 or 10−6 mm3/Nm, or even mass gain, was observed at 1000 °C. SEM observations show that tribofilms are consistently formed on the wear surfaces. A porous tribofilm, generally associated with a high wear rate at room temperature or 500 °C, is formed by compaction of debris particles. A dense tribofilm with a flat and smooth surface, often associated with a very low wear rate of the order of 10−6 mm3/Nm or less at 1000 °C, is formed by plastic deformation accompanied by dynamic recrystallization at high temperatures. A locally dense tribofilm, associated with a low wear rate of the order of 10−5 mm3/Nm at 1000 °C, is formed from the sintering of the reattached debris at high temperatures.