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Simulation of carbon tribocontacts and the crystalline-to-amorphous phase transition

Seminar Group: 


Professor Peter Gumbsch


Fraunhofer Institute for Mechanics of Materials IWM, Freiburg, Germany,
Karlsruhe Institute of Technology KIT, Karlsruhe, Germany


Friday, May 4, 2012 - 4:00pm


ESB 1001

Modelling friction and wear processes on an atomic scale is still a great challenge. It has to be chemically accurate to correctly describe bond breaking events and must yet be suitable for engineering application which requires description of macroscopic materials degradation and materials losses in engineering applications. Our aim is to reduce the complexity of engineering systems as far as possible and to demonstrate the usefulness of atomistic modelling approaches in this context. We have therefore chosen diamond and diamond like carbon (DLC) films as our initial systems to investigate.

Ab initio methods and simpler tight binding approaches are used to assess the relative importance of certain chemical changes or reactions. These methods also form the basis for the development of empirical potentials that can accurately represent bond breaking processes, which is a key ingredient in tribosimulations and not usually given enough attention. The potentials are then used for atomistic simulations of the immediate tribocontacts. Phase transitions and structural changes in these contacts are studied and found to be important for the understanding of the polishing of diamond and the wear of DLC. The crystalline-to-amorphous phase transition occurs under conditions which are very far from equilibrium thermodynamics and is governed by atomic forces rather than energy landscape. The final step in the polishing of diamond corresponds to the wear of the DLC or the burn-off of the DLC from the diamond surface.