Wetting behavior of Cu droplets on Fe Surfaces: Insights from molecular dynamics simulations

Molecular dynamics simulations were performed to investigate the wetting behavior of Cu droplets on three distinct Fe surfaces: Fe(0 0 1), Fe(1 1 0), and Fe(1 1 1). The results reveal that Cu droplets exhibit a relatively stable layering order near the solid–liquid interface on all Fe surfaces while displaying different three-phase contact line structures. Influenced by the substrate surface structure and the extent of interfacial reactions, Cu droplets demonstrate superior wettability and the fastest spreading on Fe(1 1 1) surfaces, while exhibiting the poorest wettability and lowest spreading rate on Fe(0 0 1) surfaces. The spreading of Cu droplets on all Fe surfaces exhibits a similar driving mechanism, while is applicable to different spreading kinetic models emphasizing varying dissipation channels. The wetting process comprises a fast-spreading regime driven by inertia and a slow-spreading regime governed by surface tension, with dissolution reactions further enhancing the wetting kinetics. On Fe(0 0 1) surfaces, the spreading of precursor films can be well described by the molecular-kinetic model, while the primary dissipation mechanism for the main bodies of the droplets is the viscous dissipation within liquids, consistent with the hydrodynamic model. Conversely, on Fe(1 1 0) and (1 1 1) surfaces, the main limiting factor for spreading is the friction dissipation between the main bodies of the droplets and the precursor films, in line with the molecular-kinetic model. These findings offer new insights into the wetting phenomena of metal/metal systems, particularly the liquid metal embrittlement associated with Cu(l)/Fe(s) wetting.