Measurement of hardness and elastic modulus of surface coatings is extremely important because it allows for quick estimation of the quality of the coating. Although such results are easily accessible via nanoindentation, many people are still using conventional microhardness measurements. Owing to the necessity of optical analysis of the imprint and due to the ISO requirements on its size, the penetration depth is usually too big and the properties of the substrate rather than of the coating are measured. Nanoindentation, on the other hand, can measure mechanical properties of the layer without the effect of the substrate thanks to applying sufficiently low loads and depths. The method is based on the analysis of the load-depth data and is applicable also to extremely thin coatings. Low load indentations can however bring another issue: variation of results due to surface roughness when this one is similar to indentation depth. Since indentation depth must be small enough to avoid the influence of the substrate, on rough samples the irregular contact with the surface leads to big scatter of the results. Surface preparation is therefore required to obtain reliable results.

In this work we compare the results of conventional microhardness measurements with nanoindentation measurements on several types of ceramic and metallic coatings. Hardness depth profiles obtained by dynamic nanoindentation reveal the maximum allowable indentation depth where the substrate effect can still be neglected and test parameters for correct hardness measurement of coatings are proposed. Direct comparison with conventional hardness confirms that this method shall not be used on thin coatings. The effect of surface roughness on the variation of nanoindentation results are demonstrated on surfaces with different levels of roughness showing the influence of surface roughness on the repeatability of the results. Polishing with fine diamond slurry is proposed as a quick and efficient method to decrease the scatter of nanoindentation results while removing only a small fraction of the coating. With our work we would like to contribute to a better understanding of the measurements of mechanical properties of thin coatings.