Estimation of the stress relief induced in CrN thin films by buckling

Previous studies have revealed that thin PVD coatings submitted to repeated impacts may undergo blister formation which appears to be the first damage step leading to spalling. From mechanical analysis, the blister formation is likely to be related to a critical compressive stress value depending on the film thickness and on the size of the interfacial defects. In this model, a blister formation should then lead to a local stress relief. To show this induced stress evolution, micro-Raman spectroscopy was used in this study on both untreated and buckled CrN thin films. Thanks to the localized analysis, microstructure and stress modifications in the impacted area were detected. They can be related to the mechanical model generally used to explain the observed failure mechanisms. Stress reliefs of about 1.6 and 2.2 GPa have been detected on buckled CrN films of various thicknesses whereas structural damages are observed in worn impact scares.