Coupled molecular dynamics/continuum simulations of Joule heating and melting of isolated copper-aluminum asperity contacts

Atomic-level dynamics of Joule heating, melting and plastic dynamics at loaded nanometer-scale Cu and Al asperity contacts are modeled using an ad hoc coupling between a numerical solution to a heat transport equation, a virtual resistor network for describing electric current flow and a molecular dynamics simulation using the embedded atom method. Under constant voltage conditions the simulations demonstrate the formation of an Al melt that removes faceting from a Cu asperity via surface disordering at the melt-solid interface. Constant current simulations demonstrate initial disordering of both copper and aluminum at the interface. Flow from the aluminum melt increases the contact area, which lowers the resistance and drops the voltage to below that needed for melting. For the system with a loaded copper asperity, the interface recrystallizes and the dynamics transition from molten flow to plastic damage via dislocation emission. For an aluminum asperity, the asperity remains disordered after the voltage drop and no dislocation emission occurs into the copper or aluminum substrate.