Atomic-scale insights into microscopic mechanisms of grain boundary segregation in Al-Cu alloys

This study aims to clarify the mechanisms for the grain boundary (GB) segregation through investigating the absorption of excess solute atoms at GBs in Al-Cu alloys by using the hybrid molecular dynamics/Monte Carlo simulations. Two segregation mechanisms, substitutional and interstitial mechanisms, are observed. The intergranular defects, including dislocations, steps and vacancies, and the intervals in structural units are conductive to the prevalence of interstitial mechanism. And substitutional mechanism is favored by the highly ordered twin GBs. Furthermore, the two mechanisms affect the GB structure differently. It is quantified that interstitial mechanism is less destructive to GB structure than substitutional one, and often leads to a segregation level being up to about 6 times higher than the latter. These findings contribute to atomic scale insights into the microscopic mechanisms about how solute atoms are absorbed by GB structures, and clarify the correlation among intergranular structures, segregation mechanisms and kinetics.