Effect of substrate bias voltage on structural and mechanical properties of pulsed DC magnetron sputtered TiN-MoSx composite coatings

TiN-MoSx composite coatings were deposited by pulsed DC closed-field unbalanced magnetron sputtering (CFUBMS) using separate Ti and MoS2 targets in an Ar and N2 gas environment. The effect of substrate bias voltage on the structure and mechanical properties of TiN-MoSx composite coating has been studied. The structure and composition of the coating were evaluated using field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) by X-ray and grazing incidence X-ray diffraction (GIXRD). Scratch adhesion tests, Vickers microhardness tests and ball-on-disc tests with a cemented carbide (WC-6%Co) ball were carried out to investigate mechanical properties of the coating. Application of substrate bias was found to transform the structure of TiN-MoSx composite coating from open columnar to a dense columnar structure. The changes in grain size and texture coefficient appear to be associated with variation in substrate bias voltage. The mechanical properties of the coating such as adhesion and composite microhardness were also observed to be related to the change in bias voltage. A maximum hardness of 22 GPa was obtained for a coating deposited at substrate bias voltage of −40 V. The improved structural and mechanical properties of the coating deposited at −40 V were also reflected in its excellent wear resistance property.