X-Ray diffraction characterization of pre-treated cemented carbides for optimizing adhesion strength of sputtered hard coatings

Todayʹs research activities in the field of improving the properties of cutting tools are concentrated on the optimization of manufacturing technologies and tool geometries as well as on the improvement of alloying elements and coatings of tools. Especially the field of coatings still shows a high potential to improve the wear resistance of cutting tools. As a result of the reduced machinability of new cutting tool materials high mechanical and thermal loads during grinding influence the subsurface properties of the uncoated tool heavily. Even with optimized coating parameters the deposited PVD-coatings may fail because of these properties of the substrate. Therefore, mechanical pre-treatment processes, in addition to the chemical and sputter cleaning processes are often needed to enhance the coating adhesion. In detail, the cleaning processes lead to changes in subsurface properties of the substrate. Due to the fact that the penetration depth of X-rays is in the range of several microns, X-ray analysis has a high capability for characterizing the changes in subsurfaces treated by this method. In this paper X-ray investigations are performed for surface and subsurface analyses of cemented carbide cutting tools. The change of residual stress distribution in subsurface layers due to the mechanical pre-treatment of PVD-coated carbides is investigated. Dependencies between stress distribution in subsurface layers and interface strength are highlighted. X-Ray residual stress measurements are carried out using a new method for evaluating residual stress gradients. These stress gradients are determined using the non-linear distribution of the diffraction angle vs. the tilt angle in units of sin2Ψ The results are compared with the well-known sin2Ψ method using different lattice planes which correspond to different penetration depths. In final cutting tests adhesion and wear behaviour of (Ti,Al)N-coated substrates are analysed.