The molecular dynamics and multiple histogram techniques were used to understand the core/shell formation of bimetallic silver-nickel nanostructures at sizes of 55 and 147 atoms. Two core/shell structures of 55 atoms icosahedra, Ag13Ni42 and Ni13Ag42 with their isomers, Ni-13(Ni29Ag13) and Ag-13(Ag29Ni13) were considered. In the case of 147 atoms icosahedra, homogeneous motifs (either Ag or Ni) of the core, inner shell, and outer shell were produced along with their heterogeneous isomers. Energetically, nickel-core structures are found to be more favorable than corresponding silver-core motifs. Constant volume heat capacity was used to characterize the phase transition of each cluster. The trend in the variation of melting temperatures of 55 atoms icosahedra with the nickel composition aggreses with the observed trend in the energy variation, thus values of heat capacity reveals more solid-like characteristics of NicoreAgshell motifs and liquid-like characteristic of AgcoreNishell motifs. Thermodynamic feasibility of the nickel-core/silver-shell formation was established by comparing Helmholtz free energy changes in the transition of silver atoms from the center to the shell and nickel penetration from shell to the center. The free energy changes in surface mixing and segregation of silver atoms revealed that the mixing of silver atoms with nickel atoms on the surface is more favorable than segregation. In a low nickel environment, the formation of homogeneous core/shell structures occurs, while in moderate nickel composition, mixing of silver atoms is favorable than being in the homogeneous core/shell configurations.