Deposition and modelling of novel coating systems for wear protecting coatings in cutting processes
C. Ziebert, S. Ulrich
Forschungszentrum Karlsruhe, Institut für Materialforschung I, Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany
By means of PECVD-/PVD-hybrid technology innovative concepts for wear protecting coatings with structured nanoscale dimensions can be realized. Such nanoscale multilayers or nanolaminated coatings provide for a better protection of the surface of cutting tools in dry machining, because by the alternate deposition of two different materials a new property profile can be tailored. In addition by variation of the number of layers at a constant total film thickness the amount of interfaces can be adjusted specifically and by the choice of the deposition conditions a specific interface layer design can be achieved. Different multifunctional nanolaminated coating concepts have to be compared to find the best solution for different dry cutting processes. Whereas nanolaminated coatings with a nanocomposite TiC-C component should improve the tribological properties and thus the cutting of abrasive materials, coatings with heteropolar oxide hard material component such as Al2O3 or metastable TiCSiO should increase the temperature stability and thus the possible cutting speeds for adhesive materials. The mechanical and tribological properties of these coatings, deposited onto Si, metal, hard metal and ceramic substrates on the laboratory scale, have to be characterized by micro- and nanoindentation, scanning force microscopy, scratch test, and tribometer tests. These results provide fundamental input for the validation of an atomistic modelling of the properties, which are dominated by interface effects. Thin film deposition by sputtering at low energy, film growth and interface formation processes as well as the nanoindentation experiment can be simulated by molecular dynamics(MD) methods after a potential development that relies on semi-empirical many body force fields to be adjusted to an extensive set of data obtained by ab inito calculations. At first the results from MD-simulations and experiments have to be compared and the model optimized to agree with the measured results. Then improved coatings can be designed by using predictions from advanced simulations that include material gradients within the interface regions. Especially interesting is the modelling of the modification of the residual stress profile across the interfaces in order to improve the adhesion. Experimentally the predictions from the simulations can be realized e.g. by a variation of the ion bombardment energy during the deposition of the different layers. Thus an improved combination of simulation and experiments helps to leave the heuristic stage of coating development.