Grain-boundary segregation and grain growth in nanocrystalline substitutional solid solution alloys

Abstract

A model for describing solute segregation at grain boundaries has been developed for substitutional solid solution alloys, which integrates multiple factors from atomic to microstructural scales. A concept of molar Gibbs free energy of segregation was introduced to evaluate the segregating capability of the solute elements in a closed system, through which the influences of grain boundary structure, grain size, material composition, and external conditions were described. Based on the evaluation of various energy forms related to solute segregation and grain growth processes, the nature of the thermal stabilization of nanograin structures by solute segregation was disclosed. A criterion for the destabilization of nanostructures, which is determined by the competition of the change rates between the molar Gibbs free energy of segregation and the total energy of grain boundaries with grain size, has been proposed. This study provided guideline to achieve high-temperature stability of nanograin structures of solid solution alloys even for the weakly segregating nanocrystalline systems.