Effect of crystallographic orientation on the friction and wear properties of Mo xS y–Ti coatings by pulsed-dc in nitrogen and humid air

Abstract

This work reports on the structural and wear properties of Mo x S y –Ti films, deposited on D2, 52100, and 440C steel substrates by pulsed-dc magnetron sputtering. A closed field unbalanced magnetron sputter ion plating system was used for the deposition process. The mechanical and tribological properties of Mo x S y –Ti coated composites onto selected steel substrates were characterized using microhardness test, friction–wear test in atmospheric conditions and in dry nitrogen. The X-ray diffraction (XRD) was used to determine the phase structure. Structural analysis was performed using SEM-EDS. Mo x S y –Ti films showed a very dense structure with pronounced basal plane (0 0 2) orientation, which showed the lowest friction coefficient (0.022) in dry nitrogen. The coefficient of friction can be attributed to the oxidation of MoS 2 at the wear track to form MoO x that is known to cause an increase in the friction coefficient. In humid air, an oxidative environment, the films had higher coefficient of friction (0.07), and lower wear life (142 500 passes with 2.11 × 10 −6 mm 3/N m wear rate) than in dry nitrogen, where the wear life was over 250 000 passes with the lowest wear rate of 3 × 10 −8 mm 3/N m.