Structure, mechanical and tribological characterisations of pulsed DC magnetron sputtered TiN-WSx composite coating

Abstract

Pulsed DC magnetron sputtered TiN-WSx composite coatings were investigated in terms of their structural, mechanical and tribological properties. The coatings were synthesized in Ar and N2 mixed environment from separate Ti and WS2 targets. Compositional variation was performed by systematically varying the Ti cathode current while keeping the same for WS2 cathode at a fixed value. EDS analysis of the films revealed that the cumulative (W + S) content varied from 8.9 to 42.0 wt%. The films were, however, sulphur deficient, S/W at.% ratio being in the range of 0.6–0.78. GIXRD spectra indicated coexistence of (002) oriented WS2 phase along with polycrystalline TiN phase, as confirmed by HRTEM revealing presence of WS2 in nanocluster form within TiN columnar structure. FESEM micrographs showed decrease in agglomerated grain size and densification of columnar structure with increase in (W + S) content. The adhesion also scaled with (W + S) content up to 27.8 wt%. The nanohardness of the composite coatings, however, progressively decreased from 27.3 GPa to 17.3 GPa with increasing content of (W + S). Significant reduction in friction coefficient and wear rate could also be recorded for the composite coatings, as compared to TiN, the best being obtained for the one containing 15.0 wt% of (W + S).