Microstructure and indentation response of TiN coatings: The effect of measurement method

The hardness and elastic modulus of thin films can generally only be determined directly using an ultra-low load indentation tester or indirectly using a modelling approach since there is usually a contribution from the substrate. Although the modelling approaches developed work reasonably well when there is sufficient load support from the substrate, if this shows appreciable plastic deformation during the indentation process there can be a change in the deformation mechanisms of the coating and direct and indirect measurements are less comparable. In this paper the changes in hardness and contact modulus of sputtered titanium nitride coatings deposited on stainless steel have been investigated using both direct and indirect measurement techniques as a function of thickness and applied substrate bias. The same trends in behaviour have been observed for each of the techniques though the absolute hardness values determined are not identical at low coating thickness. The usefulness of the two approaches is discussed in light of these observations. •Hardness and elastic modulus can be measured directly for thick coatings.•Good data is needed at low relative indentation depths for accurate assessment.•Microstructure (texture, grain size and packing density) affects properties.•Thin coatings on soft substrates are challenging to assess.•Models for coating hardness less reliable when substrate plastic deformation occurs.