Residual stress depth profiling of a coated WC-Co hardmetal - Part I of II: Equi-penetration grazing incidence X-ray diffraction (EP-GIXD) method

Abstract

The damage behavior of hard coated structures such as used for metalworking tools is influenced by residual stresses since they are superimposed with the load stresses that arise in application. Information on the depth gradient of these residual stresses in a coating's substrate is crucial to understand the evolution of damage in the substrate-coating composite. In the current work, the equi-penetration grazing incidence X-ray diffraction (EP-GIXD) method was adapted for the determination of the residual stress depth profile in the WC-Co hardmetal substrate below an AlCrN-based hard coating. The limits of this method in terms of coating thickness, up to which the EP-GIXD method is applicable to determine the residual stress state in the substrate, were investigated by recording the X-ray absorption in the hard coating in rocking curves. To this end, the diffraction intensity was recorded as a function of the path length in the coating that depends on the incident angle of the X-rays. Subsequently, the obtained residual stress profile was determined as a function of various mean penetration depths selected via the variation of the angle of incidence. The EP-GIXD method facilitates a significant reduction of experimental effort compared to e.g. synchrotron-based approaches for the future study of the residual stress state of substrates in substrate-coating composite structures.