Abstract
The effects of corrugated grain boundaries on the frictional properties of extended planar graphitic contacts incorporating a polycrystalline surface are investigated via molecular dynamics simulations. The kinetic friction is found to be dominated by shear induced buckling and unbuckling of corrugated grain boundary dislocations, leading to a nonmonotonic behavior of the friction with normal load and temperature. The underlying mechanism involves two effects, where an increase of dislocation buckling probability competes with a decrease of the dissipated energy per buckling event. These effects are well captured by a phenomenological two-state model, that allows for characterizing the tribological properties of any large-scale polycrystalline layered interface, while circumventing the need for demanding atomistic simulations. The resulting negative differential friction coefficients obtained in the high-load regime can reduce the expected linear scaling of grain-boundary friction with surface area and restore structural superlubricity at increasing length-scales.
Highlights
The effects of corrugated grain boundaries on the frictional properties of extended planar graphitic contacts incorporating a polycrystalline surface are investigated via molecular dynamics simulations
The system consists of a slider composed of three Bernal stacked pristine graphene (PrisGr) layers orientated at θ0 = 38.2°, and a substrate consisting of a layer of polycrystalline graphene (PolyGr) including two patches with orientation angles of θ1 = 0° and θ2 = 8°, and two Bernal stacked PrisGr layers oriented at θ3 = 0°, where the bottom one ðl6Þ is kept fixed
The PolyGr layer contains two grain boundaries (GBs) composed of lines of separated pentagon–heptagon pair dislocations along the GB (y-axis) direction (Fig. 1b)
Summary
The effects of corrugated grain boundaries on the frictional properties of extended planar graphitic contacts incorporating a polycrystalline surface are investigated via molecular dynamics simulations. The underlying mechanism involves two effects, where an increase of dislocation buckling probability competes with a decrease of the dissipated energy per buckling event. These effects are well captured by a phenomenological two-state model, that allows for characterizing the tribological properties of any large-scale polycrystalline layered interface, while circumventing the need for demanding atomistic simulations. The simplest example of polycrystalline monoatomic twodimensional (2D) surface is polycrystalline graphene (PolyGr), which is composed of randomly shaped and oriented single crystalline graphene patches separated by sharp grain boundaries (GBs) The latter are characterized by chains of lattice dislocations often including pentagon–heptagon pairs[14]. The knowledge gained in this study may provide insights regarding universal mechanisms of energy dissipation appearing in extended multi-contact rough interfaces, where the formation and rupture of contacts dictates the friction[22,23,24,25,26,27]
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