Solid-liquid interfacial free energy and its anisotropy in the Cu-Ni binary system investigated by molecular dynamics simulations

The solid-liquid interfacial free energy γ and its anisotropy in the Cu-Ni binary system were measured by using molecular dynamics simulations coupled with the capillary fluctuation method (CFM) based on an embedded atom method potential. It is found that both the interfacial energy and its anisotropy are enhanced with the increasing of the coexisting temperature, significant variations are however observed in the anisotropy parameters. Nonetheless, the anisotropy relationship is hardly modified, and the inequality γ100 > γ110 > γ111 holds for all temperatures studied. By projecting the calculated anisotropy parameter ε1 and ε2 onto the dendrite growth direction selection map, one finds that a <100> dendrite is generally favored for the Cu-Ni alloys. Upon alloying, the preferred dendrite growth direction shifts to the vicinity of the boundary between the <100> and hyper-branched regions, indicating the possibility of a transition of solidification morphology from a <100> dendrite dominated to a hyper-branched one. These predictions agree well with and explain the experimental observations during the equilibrium and non-equilibrium solidifications in the Cu-Ni alloy systems.