Point defect interactions with Guinier-Preston zones in Al-Cu based alloys: Vacancy mediated GPZ to θ′-phase transformation

The energetics of point defect interactions with a Guinier-Preston zone (GPZ) in Al alloys are systematically studied using ab initio calculations and a supercell approach. We find that vacancies can be trapped by GPZs and that the presence of a vacancy in a Cu layer qualitatively changes the solute–GPZ interactions. A vacancy mediated mechanism of GPZ to θ′-phase transformation is suggested and shown to be thermodynamically feasible, which involves the formation of structural vacancies and splitting of a GPZ layer into two half-vacant Cu layers. This mechanism, in combination with the calculated attractive solute-vacancy interactions, is predicted to result in the solute segregation at the interface between Al matrix and the forming θ′-phase precipitate.