Development of martensitic support layers for hard coatings for optimized properties of surface layers by local electron beam (EB) hardening

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The excellent characteristics of PVD layers, as high hardness and wear resistance, can only be exploited on substrates with sufficient load-bearing capacity, e.g., on tool steels. The use of PVD layers on tribologically stressed components made of softer steels (51CrV 4) makes additional surface hardening necessary. Due to its unique process-specific characteristics - as high power density, flexible and highly dynamic energy modulation, and treatment under vacuum - Electron Beam Hardening (EBH) is eminently suitable to ensure local, stress-optimized improvement of the load-bearing capacity of the steel. The subject of the research project is the innovative combination of PVD coating with subsequent EBH. The research approach of the project is twofold: On the one hand, to increase considerably by means of EBH the supportive function of the substrate surface layer under Ti1-xAlxN layers deposited by magnetron sputtering and, on the other hand, to research in depth the effects of that thermal input on the structural composition and properties of the PVD layer. During phase 1 of the project, significant findings were made regarding the influence of the chemical composition and layer thickness of the Ti1-xAlxN on its behavior during EBH. In the projects 2nd phase, the scientific principles shall be deepened further in the area of promising layer/EB-treatment variations, and shall be expanded to develop new and important insights into the microstructure and wear behavior of such surface-layer combinations. In the 1st project period, the occurrence of layer defects such as cracking, flaking, and delamination could be contained, but not completely eliminated. Accompanied by a mathematical simulation of the internal stresses, the causes of such damage shall be derived, and tailor-made multilayer and graded layer systems generated to minimize damage potential with respect to the subsequent EBH. Moreover, crack-free surface layer combinations with application-relevant thicknesses shall be produced. Furthermore, insufficiently understood phenomena brought about by the EB treatment of the Ti1-xAlxN layers shall be researched, especially locally restricted diffusion and micro-melting at the interface between the PVD and EBH layers. In this context, the extent to which targeted utilization of these effects is relevant for the improvement of layer adhesion must be clarified. Key concerns of the 2nd project period further shall be the research of the mechanism of energy absorption by inhomogeneous absorption layers during EBH, as well as the examination of thermally induced phase transformations in Ti1-xAlxN. These transformations make possible the local modification by EB action of internal stresses and, therefore, of the layer hardness. The EBH treatment shall also be realized using the Flash technique, as opposed to the EB hardness field (CI Technique) used to date. Targeted one-dimensional heat dissipation can thus be realized for defined samples.