Effect of coated edge geometry on internal stress distribution in multilayered coatings

Abstract This paper presents results of computation internal stresses in several types of hard coatings deposited on rounded edges whose radii are of the same order as the coating thickness. The model of a coated substrate is a straight edge consisting of two planar surfaces with varying opening angle α joined by cylindrically shaped surface. The internal stresses are computed by the finite element method. Four different combinations of TiTiN multilayers are studied and especially the peak values of internal stresses in the interface are compared. It is shown that in multi-layer sandwich coatings, the maximum stress values are lower, nevertheless, the most important role has the ratio coating thickness/edge radius. For this reason, in order to suppress the stress in the coating-substrate interface in the coated edge, a special care should be denoted to the edge smoothing before the deposition process. It is also shown that the optimum coating model is a bilayer coating consisting of a gradual Ti–TiN interlayer and outer layer of stoichiometric TiN.