Formulated self-lubricating carbon coatings on carbide ceramics

SiC and Ti3SiC2 are very important materials for many tribological applications. However, they are not lubricious under dry sliding. Chlorination was conducted at 1000 °C for 5 h in a quartz tube to fabricate carbide-derived carbon (CDC) coatings on SiC and Ti3SiC2 blocks. Unlubricated sliding friction and wear tests were conducted on a UMT-2MT tribometer with a ball-on-block configuration. Compared to bare SiC and Ti3SiC2 blocks, SiC and Ti3SiC2 blocks with the CDC coatings were self-lubricating in sliding against a Si3N4 ball at room temperature. The wear of the Si3N4 ball was too low to measure in sliding against the CDC coatings. In addition, the CDC coating on a SiC block took advantages over the CDC coating on a Ti3SiC2 block in terms of friction coefficient, wear resistance and load-carrying capacity. The microstructure of the two CDC coatings was characterized by three aspects, i.e. pore size, grain size and shape, and composition (carbon species). The two CDC coatings are highly porous materials but of different grain size, grain shape and composition. The CDC coating on SiC was composed of nanocrystalline and disorder carbon of equiaxed grains while that on Ti3SiC2 was composed of plate-like microcrystalline graphite. The microstructural effect on the tribological behavior of the CDC coatings on SiC and Ti3SiC2 blocks was investigated and discussed.