Abstract
Effect of hard TiN underlayer on mechanical and wear characteristics of TiN-WSx composite coating was studied. A mono layer TiN coating was also incorporated in the study as a reference. The coatings were synthesized with pulsed magnetron sputtering process. Structural properties were investigated with field emission scanning electron microscopy, energy dispersive spectroscopy, grazing incidence x-ray diffraction; mechanical properties with scratch adhesion test, nanoindentation test and finally tribological properties were studied with pin-on-disc test. TiN underlayer resulted in a more compact morphology of top TiN-WSx hard-lubricious layer. WS2 phase with (002) orientation coexisted with crystalline TiN for TiN-WSx composite both with and without hard TiN underlayer. Scratch test revealed 35% increase in critical load of adhesion for TiN-WSx/TiN dual layer structure as compared to TiN monolayer. Brittle flaking of TiN along edges of scratch track also became negligible for dual layer coating owing to presence to soft WSx as well as presence of hard under layer which hindered substrate deformation during scratching. Low hardness of TiN-WSx as compared to TiN, partially recovered owing to addition of hard TiN underlayer. The dual layer coating also exhibited significantly low coefficient of friction of approximately 0.25–0.3 relative to 0.7–0.8 for TiN. The hard TiN underlayer reduced ploughing of top TiN-WSx composite layer. This in turn, resulted in low wear loss and subsequently less accumulation of wear debris at the leading edge of the counterbody.
Published Version
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