Activation of pyramidal II <c+a> slips at room temperature in Mg-Zn-Y 18R and 14H long-period stacking ordered phases

The 18R and 14H long-period stacking ordered (LPSO) phases were generally considered that only the basal and non-basal <a>slips and kink banding could be activated during quasi-state deformation at room temperature. Here, we confirm that the pyramidal II <c+a> slips can also be activated in the 18R LPSO phase by quasi-state nanoindentation and in the 14H LPSO phase by cold roll with a rolling direction parallel to the (0001) plane. Due to the interaction between the Zn₆Y₈ atomic clusters in the LPSO phases and the pyramidal II <c+a> dislocations, the pyramidal II slips are localized in the well-defined slip bands while the chemically ordered structure of Zn₆Y₈ atomic clusters is disrupted to be disordered. Additionally, the interaction also induces Zn/Y atoms segregation at the two edges of the slip band. Our results unravel the origin for the excellent room temperature plasticity in the LPSO phases.