Formation and Relative Stabilities of Core-Shelled L1 2 -Phase Nano-structures in Dilute Al–Sc–Er Alloys

First-principles thermodynamic calculations were carried out at the interface level for understanding the precipitation of coherent L12-phase nano-structures in dilute Al–Sc–Er alloys. All energetics, relevant to bulk substitution, interface formation, interfacial coherent strain and segregation, were calculated and used to evaluate the nucleation and relative stabilities of various possible L12 nano-structures. Only matrix-dissolved solute Er (or Sc) can substitute Sc (or Er) in L12-Al3Sc (or Al3Er). The inter-substitution between L12-Al3Sc and Al3Er is not energy feasible. Ternary L12-Al3(ErxSc1−x) precipitates tend to form the Al3Er-core and Al3Sc-shell structure with a sharp core/shell interface. Three possible formation mechanisms were proposed and examined. The effects of Er/Sc ratio and aging temperature on the relative stabilities of L12-phase nano-structures in Al were also discussed.