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

Today's research activities in the field of improving the properties of cut ting tools are concentrated on the optimization of manufacturing technologi es and tool geometries as well as on the improvement of alloying elements a nd coatings of tools. Especially the field of coatings still shows a high p otential to improve the wear resistance of cutting tools. As a result of th e reduced machinability of new cutting tool materials high mechanical and t hermal loads during grinding influence the subsurface properties of the unc oated tool heavily. Even with optimized coating parameters the deposited PV D-coatings may fail because of these properties of the substrate. Therefore , mechanical pre-treatment processes, in addition to the chemical and sputt er 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 t he range of several microns, X-ray analysis has a high capability for chara cterizing the changes in subsurfaces treated by this method. In this paper X-ray investigations are performed for surface and subsurface analyses of c emented carbide cutting tools. The change of residual stress distribution i n subsurface layers due to the mechanical pre-treatment of PVD-coated carbi des is investigated. Dependencies between stress distribution in subsurface layers and interface strength are highlighted. X-Ray residual stress measu rements are carried out using a new method for evaluating residual stress g radients. These stress gradients are determined using the non-linear distri bution of the diffraction angle vs. the tilt angle in units of sin(2)psi Th e results are compared with the well-known sin(2)psi method using different lattice planes which correspond to different penetration depths. In final cutting tests adhesion and wear behaviour of (Ti,AI)N-coated substrates are analysed. (C) 2001 Elsevier Science BN. All rights reserved.