Residual stress analysis of thick film systems by the incremental hole-drilling method

Residual stresses: play an important role in coating systems as they determine their properties as well as their life-time behavior. In many industrial applications multi-layer systems are used. This work examines the applicability of the incremental hole drilling method to determine residual stress states in multi-layer coating systems, i.e. in the top-layer, in the interlayer and in the substrate. For this purpose systematic finite element (FE) simulations are carried out. Initially, the interfaces were assumed to be planar and subsequently rough interfaces were considered. The results indicate that thin interlayers with layer thicknesses smaller than 30 μm can be neglected in the evaluation of the measured strain relaxations, since they lead only to a minor stress deviation. In case of larger interlayer thicknesses a case-specific calibration, taking into account the exact build-up of the multilayer system, results in reliable determinations of the residual stress states, in the top-layer, the interlayer and the substrate. Finally the simulation results are applied to a model thick film system consisting of a thermally sprayed Al2O3-coating on a fine-grained construction steel (S690QL). Its residual stress state is determined experimentally by the incremental hole-drilling method. © Carl Hanser Verlag GmbH & Co.