Sliding Friction-Induced Tribochemical Processes

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In high-load tribological contacts, complex boundary layer dynamics can be observed, which are influenced for example by the contacting surfaces, material loss, and wear dust. These dynamics are directly related to macroscopic properties of the contact, such as the friction coefficient, wear, temperature, and emissions, and directly influence the dynamics of these phenomena. These interdependencies result in part from tribochemical processes on the friction elements and wear particles. Thermal inhomogeneities are the primary trigger for these tribochemical processes, and can result from local concentrations of dissipation energy in the tribological contact. This can be brought about by temporary contact islands which are formed from local concentrations of boundary layer particles.The aim of this project is to develop approaches for considering these chemical phenomena, and to investigate their influence on tribological output parameters. Various methodologies are implemented, such as tribological measurements, characterization and analysis of surface topography and surface chemistry, modeling, and simulation. For these investigations, a variety of minimal friction materials are produced by the applicants. Various components are specifically chosen in order to systematically evoke chemical reactions. The tribological investigations are primarily carried out on a self-designed, highly automated tribometer (AUT). A variety of surface analysis methods are implemented, e.g. EDX, XRD, SIMS, FIB-REM and TEM. These closely interlinked investigations are intended to demonstrate the potential for identifying chemical processes and the associated influences. This is achieved through parameter selection and variation of the components in the minimal mixtures. It should also be determined whether there are material components with which the global dynamics of friction and wear can be chemically influenced. The applicants aim to improve the understanding of these dissipation mechanisms as they apply to macroscopic friction in high-load contacts. A general procedure for the investigation and characterization of tribochemical boundary layers is to be developed, which could then be applicable to various high-load friction pairs.