Tribological duality of Ti3SiC2

We report here on the friction behavior of fine- and coarse-grained Ti3SiC2 against steel and Si3N4 balls. Two successive friction regimes have been identified for both grain sizes and both counterparts. First, Type I regime is characterized by a relatively low (0.1-0.15) friction coefficient, and very little wear. Sliding occurs between a tribofilm on the ball and the Ti3SiC2 plane when against steel. Then, a Type II regime often follows, with increased friction coefficients (0.4-0.5) and significant wear. Compacted wear debris seems to act as a third body resulting in abrasion of the ball, even in the case of Si3N4. The transition between the two regimes occurs at different times, depending on various factors such as grain size, type of pin, and normal load applied. Some experiments under vacuum showed that the atmosphere plays also a major role. The reason for this evolution is not fully clear at that time, but its understanding is of major technological importance given the unusual good properties of this material.