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.