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

The aim of the present work was to investigate the microstructure evolution of the nanostructured Cr/CrN multilayer coatings on titanium Ti6Al4V alloy during indentation. Five types of multilayer (Cr/CrN) × 8 coatings were deposited on Ti6Al4V titanium alloy by the PVD vacuum arc method. The coatings had the same total thickness and number of constituent layers, but differed in the thickness ratio of the Cr and CrN constituent layers (QCr/CrN parameter). The indentation measurements were performed with a Berkovich indenter at loads of 100 mN, 500 mN, and 1 N. The SEM and STEM observations were focused on the cracking behaviour in the CrN layers as well as on the microstructure changes in the ductile Cr layers. vestigations 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.