A FEM-based analytical-experimental method for determining strength properties gradation in coatings after micro-blasting

The superficial mechanical properties of PVD films can be changed by micro-blasting. This process might induce a material deformation and herewith strength properties enhancement up to a certain depth from the coating surface. Depending on the micro-blasting conditions, the deformed film depth varies, thus affecting the coating's performance in different applications. In the paper, a novel method is introduced for determining mechanical strength properties gradation in coatings after micro-blasting. Coated cemented carbides inserts were micro-blasted at various pressures. Employing the X-ray diffraction technique, the residual stresses were measured in the coating before and after micro-blasting and the related stress changes were determined at a certain depth from the film surface. These changes were compared to corresponding ones, calculated by a developed algorithm based on the Finite Elements Method (FEM). This algorithm describes the continuous penetration of individual blasting grains into the coating material and determines residual stresses after micro-blasting. Considering these results, the grain penetration depth and moreover, the developed distribution of the film yield stress after micro-blasting versus the coating thickness were estimated. To validate the captured gradation, this was taken into account in a FEM simulation of nanoindentation in micro-blasted TiAlN coatings. The obtained results were compared to corresponding measured ones leading to intuitively sound results. In all FEM calculations presented in the paper, only material stress-strain laws and no further physical or chemical properties were required. These laws were determined via nanoindentations and appropriate results evaluation.