The relation between ductility and stacking fault energies in Mg and Mg-Y alloys
S. Sandlöbes, M. Friák, S. Zäfferer, A. Dick, Z. Pei, L. Zhu, J. Neugebauer, D. Raabe.
Acta Materialia, 60, 3011-3021, (2012)
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.
Keyword(s): ultra-lightweight applications; ab-initio calculations; close-packed metals; 1st-principles calculations; molecular-dynamics; hcp metals; magnesium; deformation; twins; slip