Thermal structural disorder and melting at a crystalline interface

Thermal disordering and melting at a grain boundary are investigated by molecular dynamics in an internally consistent simulation model that avoids a number of pitfalls of earlier models. The bulk melting temperature ${\mathit{T}}_{\mathit{m}}$ of the model system, specified by an embedded-atom-method potential function fitted to aluminum, is first determined by observing directly surface-nucleated melting in a single-crystal cell with free surfaces. Simulation is then carried out on a bicrystal cell with a high-angle symmetrical tilt grain boundary on the (1¯30) plane. Profiles across the interface of local structural order and energy, along with data on atomic mobility, are obtained at several temperatures from below ${\mathit{T}}_{\mathit{m}}$ to above ${\mathit{T}}_{\mathit{m}}$; the results indicate that melting is nucleated at the grain boundary in a similar manner as at the free surface, and that there is no evidence of premelting. In the surface region as well as the grain-boundary core, thermal disordering at temperatures below ${\mathit{T}}_{\mathit{m}}$ was observed with characteristic metastable behavior commencing at about 0.93 ${\mathit{T}}_{\mathit{m}}$. The temperature variation of the interfacial thickness suggests that the onset of disordering is a continuous process.