Ultra-low friction for a layered carbide-derived ceramic, Ti3SiC2, investigated by lateral force microscopy (LFM)

The carbide-derived ceramic Ti3SiC2 has a layered structure with double TiC-like blocks separated by planes of Si in six-fold coordination. It also has an unusual combination of electrical, thermal and mechanical properties. The polycrystalline ceramic exhibits a preferred plane of easy cleavage. Fracture/cleavage faces have been investigated by lateral and atomic force microscopy, scanning electron microscopy and other techniques. The results show that the ceramic is an exceptional solid lubricant. Freshly prepared (by fracture, abrasion or scraping) cleavage faces exhibit coefficients of friction at or below the limit of resolution, about 2 x 10(-3), which are comparable to the lowest values measured for the best solid lubricants (MoS2 and graphite). Exposure to air leads to slight degradation, but values below 5 x 10(-3) were obtained after exposures of several months. Analysis of other faces leads to outcomes in the range 0.1-0.3, which are consistent with the outcome of macroscopic analysis. The favourable mechanical and electrical properties, in combination with ultra-low solid friction, may have important technical implications.