Molecular dynamics characterization of the contact between clean metallic surfaces with nanoscale asperities

Abstract

We use molecular dynamics (MD) simulations to characterize the tensile strength of contacts formed between various clean platinum surfaces with nanoscale asperities. Both commensurate contacts between (001) and (111) Commensurate contacts lead to stronger bridges than incommensurate ones but only during the initial closing events, after steady state is achieved commensurate and incommensurate (001) surfaces lead to bridges of similar strengths.

Size-dependent hardness of nanoscale metallic contacts from molecular dynamics simulations

“…This leads to a decrease in hardness with decreasing contact length since dislocations are localized within the high-stress, thin contact regions. 16,17 The atomic mechanisms that govern size effects in asperity/asperity and flat/asperity are similar. However, the dislocation structures generated show some differences.…”

“…The transition from hardening to softening is reminiscent of the Hall-Petch maximum in nanocrystalline or nanolaminate materials [13][14][15] but is governed by very different mechanisms. The hardness of these nanoscale contacts is between 50% and 70% larger than their corresponding tensile strength, 16,17 and their size effects exhibit similarities and interesting differences.…”

“…This external force (F ext ) is applied to all atoms within a thin slab (4.5 nm thick) at the free surfaces away for the contacting ones. 16,17 As described in Sec. II C, this closing force increases in a stepwise manner to characterize the elastic loading and plasticity in the contacting regions.…”

“…As is commonly done in atomistic simulations of fcc metals, 16,17 we identify dislocation activity by tracking atoms with hexagonal close packed local environments. Two consecutive planes of hcp atoms form the stacking fault ribbons that separate partial dislocations in fcc metals.…”

“…19 This potential was parameterized to reproduce the equilibrium lattice constant, sublimation energy, elastic contacts, and vacancy formation energy of Pt from experimental data and was used to study the strength of contacting bridges between rough surfaces, leading to predictions in good agreement with experiments. 16,17 Each simulation involves two 20-nm-thick Pt slabs with either a flat surface or a sinusoidal surface given by…”