Investigation of influence of design on residual stress at free edge of multilayer Ti/AlN coatings by PVD using FEM

Multilayer coatings have the advantage of controlling residual stress that is difficult to achieve with monolayer and bi-layer coatings. In this context, finite element modelling was employed to verify the effect of the design of the magnetron sputtered multilayer Ti/AlN coatings on the distribution of residual stress. Literature survey shows that most of the models in this area effectively show the residual stress arising due to thermal effects. However, that due to intrinsic effect is often neglected. In this work, the intrinsic stress was calculated using the model proposed by Windischmann and the results were incorporated in the finite element model to evaluate the total residual stress. The model was validated for residual stresses evaluated by X-ray diffraction, published by Sprute et al. It was applied for a variety of designs with bilayer and multilayer coatings (up to 20 layers) with graded and constant layer thicknesses. It was found that for the same total thickness of coatings, the residual stress is influenced by the number of layers and the thickness of individual layers. Moreover, the presence of the ductile Ti layer sandwiched between the ceramic nitride layers provides the perfect design for reducing residual stress and improving the life of the tool.