First-principles density functional theory total energy calculations, based upon pseudo-potentials and a plane-wave basis, were used to assess the stability of periodic structures with different stacking sequences in Mg–Zn–Y alloys. For pure Mg, it was found that the 6-layer (6l) structure with the ABACAB stacking was most stable after the lowest-energy hexagonal close-packed (2l) structure with ABAB stacking. The addition of 2at%Y led to stabilization of the structure to 6l sequence whereas the addition of 2at%Zn made the 6l energetically comparable to that of the hexagonal close-packing. Stacking faults on the basal plane of 6l structure was higher in energy than that of the hexagonal close-packed 2l Mg, which further increased upon Y doping and decreased significantly with Zn doping. The stacking fault energy surface for prismatic slip indicated activation of non-

basal slip in alloys with a 6l structure. Charge density analysis showed that the 2l and 6l structures were electronically similar which might be a cause for better stability of 6l structure over a 4l sequence or other periodic structures. Thus, in an Mg–Zn–Y alloy, Y stabilizes the long periodicity, while its mechanical properties were further improved due to Zn doping.

Structure and Stacking Faults in Layered Mg–Zn–Y Alloys - a First-Principles Study. A.Datta, U.V.Waghmare, U.Ramamurty: Acta Materialia, 2008, 56[11], 2531-9