Failure and deformation mechanisms during indentation in nanostructured Cr/CrN multilayer coatings

The investigations demonstrate that the applied surface treatment significantly improves the hardness of the titanium alloy. The hardness of the coatings varied in the range 10 to 35 GPa, depending on the thickness ratio of the layers. Observations performed on cross-sections through the indentation zones revealed small radial cracks, which were observed only in the CrN layers. They initiated at the interface and propagated across a given layer, to be arrested at the next interface. The STEM observations also showed microstructure changes in the Cr layers due to the accommodation of plastic deformation. The two main mechanisms of permanent deformation were observed.