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 Tₘ 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 Tₘ to above Tₘ; 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 Tₘ was observed with characteristic metastable behavior commencing at about 0.93 Tₘ. The temperature variation of the interfacial thickness suggests that the onset of disordering is a continuous process.