Thermodynamics of stable nanocrystalline alloys: A Monte Carlo analysis

A Monte Carlo simulation method is used to study the energetics and configuration of binary alloys when grain boundary states are included as potential equilibrium features. For certain sets of alloy properties, a nanostructured grain assembly is found to be the most energetically favorable state, and is stabilized by grain boundary segregation of solute. The conditions for stability against grain coarsening and the "grain boundary energy" requirement are clarified, with emphasis on the closed system conditions that prevail in nanostructured alloys. Two thermodynamic parameters, the grain boundary area potential and the grain boundary formation energy, are quantitatively disentangled and shown to differently reflect grain stability and the energy state of interfaces. These discussions provide insights on how alloying can be used to actively manipulate nanocrystalline grain sizes.