A model for wet silicon carbide tribo-corrosion
Silicon carbide sustains chemical and mechanical deterioration during tribological exposure under water lubrication. In particular, tribochemical wear leads to the formation of a thin (tens to hundreds of nanometre) layer composed of nanoscale SiC wear debris embedded in a silica-like matrix (SiOxHy) with possibly some minor oxycarbidic content. The SiC wear particles are plastically deformed and rounded as a result of mechanical tribolapping. Below that layer, subsurface damage builds up in the form of dislocations, ruptures and shear cracks. As a result of plastic deformation (similar to indentation plasticity) SiC single crystals within that transition zone are transformed into mosaic crystals with smaller domains due to slip plane gliding. Comparing results for static hydrothermal cond itions (using a hydrothermal diamond anvil cell) and tribotest for the mild and severe wear regime (i.e., with and without external cooling) we derived a qualitative wear-model of wet silicon carbide tribo-corrosion. While mechanical contact yields pathways for water inflow and generally disrupts the structural integrity of SiC grains, hydrothermal reactions of trapped water and subsequent pressure relief leads to a mechanism of dissolution and reprecipitation. The latter produces the observed amount of SiOxHy which acts as an adhesive for the SiC wear debris.