(677e) Reactive Atomic Simulations of Kinetic Friction and Its Velocity Dependence at SiC/SiC Interfaces

Silicon Carbide, SiC, is a promising candidate for advanced braking systems due to its many unique properties such as high mechanical strength, thermal shock resistance, high thermal conductivity, and resistance to both acidic and alkali environments.  The efficient design of such brakes for specific applications has, however, been a challenge.  This stems from the fact that it is of critical importance to understand how mechanical deformations, relating to friction at the interface between two surfaces, behave.  Concurrently, such reactions as oxidation, that also occur at the interface, represent another aspect of complexity to the problem.  Such factors and their impact on high-performance brakes are not understood yet.  Therefore, without a fundamental, atomic-scale understanding of what happens during the friction process, it would be impractical to optimize the design of SiC brakes for use under extreme conditions.  The purpose of this work is to investigate kinetic friction during dry sliding along the atomistic scale boundary between two SiC/SiC bilayers in both a vacuum and in the presence of air.

We have developed a reactive force field (ReaxFF) that describes the interactions between the constituent atoms, the effect of high temperature, and the reactions between the SiC atoms and the air.  The amorphous SiC structure was generated during reactive molecular dynamics using ReaxFF.  Dynamic simulations have been carried out on a pair of SiC unit cells representing the opposing surfaces at the optimal distance, 2.4 Å, wherein the potential energy is at a minimum.  Important properties, such as the energy distribution, the kinetic frictional force, the shearing distance, and shearing deformation, have been calculated as a function of sliding distance at the interface and compared under a variety of conditions.

The interfacial properties were found to play a crucial role in the sliding mechanism.  The passivated atoms at the interface, either oxidized or hydrogenated, manifest different thermo-mechanical properties as compared to unsaturated surfaces.  Therefore, controlling the surface properties with the information extracted from atomistic-level simulations can greatly help to improve the properties of SiC- type brakes.  In addition, thermal effects that result from varying the interface velocity and its subsequent impact on the friction properties of the material were studied.