Friction and adhesive wear of titanium carbide and titanium nitride overlay coatings

Abstract

The coefficient of friction and self-adhesive wear were studied for hard overlay coatings (4–8 microm thick) of TiC and TiN deposited on 304 stainless steel, titanium and aluminum discs and 440 C stainless steel riders by activated reactive evaporation process. The hard overlay coatings were characterized by X-ray diffraction and indentation hardness techniques. The frictional and adhesive wear behavior were evaluated using a standard pin-on-disc tribotester in dry and lubricated conditions. The coefficient of friction and the wear were very much lower when the test couple consisted of a hard coating rubbing against a hard coating than when one or both of the components were uncoated metals, even in dry (unlubricated) conditions. In some instances of the hard-hard couple, very low coefficients of friction (0.05–0.1) and very low wear, i.e. wear groove depths less than 1 × 10 −5 in, were observed for test conditions of a run distance of 500 m under a load of 0.4 kgf in dry conditions. From examination of the wear scar the failure mode of the coating was observed to be microfragmentation resulting from the initiation and propagation of microcracks at the rider-disc interface.