Deformation mechanisms, activated slip systems and critical resolved shear stresses in an Mg-LPSO alloy studied by micro-pillar compression

We study the micro-mechanical behaviour of single-crystalline long-period-stacking ordered (LPSO) structures, alpha-Mg and bi-crystalline Mg/LPSO micro-pillars, all cut from the same Mg97Y2Zn1 (at.%) alloy. To investigate the deformation and co-deformation mechanisms of Mg-LPSO alloys we performed micro-pillar compression experiments with micro-pillars of an orientation inclined by 7 degrees, 46 degrees and 90 degrees to (0001) orientation, respectively. Electron backscatter diffraction-assisted slip trace analysis and post-mortem transmission electron microscopy analysis showed predominant deformation by basal < a > dislocation slip in 46 degrees(0001) and 7 degrees(0001) oriented micro-pillars. In 7 degrees(0001) oriented micro-pillars additional non-basal dislocation slip and the formation of micro shear bands along pyramidal planes were activated in the alpha-Mg and the LPSO structure, respectively. In 90 degrees(0001) oriented micro-pillars (1 (1) over bar 00) [(11) over bar 20] prismatic slip was predominantly activated during the early deformation stages. The relative magnitude of the critical stresses depends on the crystal phase as well as the crystallographic orientation, i.e. the activated slip system. Specifically, basal < a > slip has the lowest critical resolved shear stress in both, alpha-Mg and the LPSO structure, while the CRSS of prismatic < a > slip is about 5 times higher than basal < a > slip in alpha-Mg and about 15 times higher than basal < a > slip in LPSO. (C) 2018 Elsevier Ltd. All rights reserved.