A dynamic FEM simulation of the nano-impact test on mono- or multi-layered PVD coatings considering their graded strength properties determined by experimental-analytical procedures

Nano-impact test is a reliable method for assessing the brittleness of PVD coatings with mono- or multi-layer structures. For the analytical description of this test, an axis-symmetrical Finite Element Method (FEM) model was developed using the LS-DYNA software. This software was adequate to simulate the progressive superficial coating fracture induced by the repetitive nano-impacts during the nano-impact test. The coating possesses one or more individual layers with own mechanical properties, since every layer after its deposition at the PVD process temperature is exposed to an annealing affecting its strength data. The annealing duration of each layer is associated with the rest time, up to the deposition of the overall coating thickness. For simulating this procedure and estimating the related mechanical properties of the coating layers, cemented carbide specimens with the same TiAlN PVD (Physical Vapor Deposition) coating of various thicknesses and structures were annealed in vacuum. The annealing duration was equal to the deposition time required for coating a specimen with a further layer up to a constant overall thickness. The superficial strength properties of these coatings were determined via nano-indentations, coupled with FEM calculations to estimate the corresponding stress-strain curves. Results obtained by the developed FEM model simulating the nano-impact test were compared with experimental ones. Taking into account the sufficient convergence between them, the introduced numerical procedure can be effectively employed to evaluate the effect of various coating structures on their brittleness.