Residual stress depth profiling in complex hard coating systems by X-ray diffraction

X-ray residual stress analysis on multilayered coating systems is a quite difficult and demanding procedure. To obtain information on both, the individual sublayers the coating consists of and the interfacial substrate region, it is necessary to apply different methods which are complementary with respect to the accessible information depth. Based on the concept of an 'equivalent thickness' for describing angle-dispersive diffraction in multilayer structures, a method is proposed that allows for the evaluation of steep intra — as well as interlayer stress gradients within the upper sublayers of multilayer coating systems. Furthermore, energy-dispersive diffraction is shown suitable to detect the residual stress distribution in the near interface substrate zone beneath the coatings. The applicability of the approaches introduced here is demonstrated by the example of cemented carbide WC/Co cutting tools being coated by chemical vapor deposition with sequences of Al2O3/TiCN sublayers.