Deformation mechanisms and mechanical properties of (0001) Mg-Zn-Y 18R-LPSO single crystals

A promising Mg-Zn-Y alloy with the long-period stacking ordered (LPSO) second phase has been developed for about twenty years. Because the LPSO phase has the unique 18R crystal structure, particularly for its packing sequence along [0001], as well as it plays an important role in strengthening mechanisms, it is interesting to clarify in terms of mechanical properties and deformation mechanisms. In this study, uniaxial micro-pillar compression tests are conducted on LPSO along the [0001] direction. At the same time, nanoindentation system equipped with the Berkovich tip is used to extract the basic mechanical properties of (0001) plane. The basal dislocations are found to be activated first, causing the bending of the sample. The bending would lead to the shear stress field downward and thus would cause the nucleation and movement of prism dislocations with [0001] Burgers vector. Prism dislocations can form the fatal 45° slip trace inside the micro-pillar and finally go through the whole sample causing fracture. The basal dislocations are found at the Zn₆Y₈-Mg interface which might be originated from the local strain field between them.