Tribo-layer formation during sliding wear of TiN coatings

The effects of atmospheric humidity and microstructure of counterface materials on the formation of tribo-layers on TiN coatings have been investigated. Pin-on-disc sliding wear experiments were conducted on physical vapour deposition (PVD) TiN-coated high speed steel (HSS) discs against HSS, mild steel and A356 Al–15% SiC pin materials under conditions of low and high relative humidity (RH). The TiN coatings undergo rapid wear by tribochemical oxidation and polishing at low sliding speeds and contact loads. This effect is reversed when contact loads and sliding speeds are raised and tribochemical wear is diminished. Increasing the humidity raises TiN wear rates and tribochemical wear seen at low loads and speeds, extending these phenomena to higher loads and sliding speeds. Hard abrasive inclusions or particles (e.g. SiC) in the counterface material prevent the formation of stable tribo-layers on the TiN surface and accelerate tribochemical wear effects by microabrasion of the TiN, particularly at high RHs.