The relation between ductility and stacking fault energies in Mg and Mg-Y alloys

The underlying mechanisms that are responsible for the improved room-temperature ductility in Mg-Y alloys compared to pure Mg are investigated by transmission electron microscopy and density functional theory. Both methods show a significant decrease in the intrinsic stacking fault I-1 energy (I-1 SFE) with the addition of Y. The influence of the SFE on the relative activation of different competing deformation mechanisms (basal, prismatic, pyramidal slip) is discussed. From this analysis we suggest a key mechanism which explains the transition from primary basal slip in hexagonal close-packed Mg to basal plus pyramidal slip in solid solution Mg-Y alloys. This mechanism is characterized by enhanced nucleation of < c + a > dislocations where the intrinsic stacking fault I-1 (ISF1) acts as heterogeneous source for < c + a > dislocations. Possible electronic and geometric reasons for the modification of the SFE by substitutional Y atoms are identified and discussed. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.