Plasticity and crack extension in single-crystalline long-period stacking ordered structures of Mg85Zn6Y9 alloy under micro-bending

Abstract

Micro-bending tests were performed on single-crystalline cantilever beams of long-period stacking ordered (LPSO) structures of Mg85Zn6Y9 alloy with and without a notch to study crystal plasticity and cracking behaviour under basal and non-basal slip conditions. The activation of basal slip induced load drops during the deformation of a plain cantilever beam with the bending moment perpendicular to the basal plane. A cantilever sample oriented for prismatic slip exhibited high yield stress and moderate strain hardening. The apparent critical resolved shear stress (CRSS) for prismatic slip was determined to be ∼360 MPa, significantly higher than 30 MPa CRSS determined for basal slip. A crystal plasticity finite element analysis of the micro-bending test on the sample oriented for prismatic slip was performed to verify the CRSS values determined. In addition, the intrinsic fracture resistance for crack growth along the <a> direction on a prismatic plane is higher than that for crack growth along the <a> direction on a basal plane. In combination, these results indicate that inhibition of basal slip activity contributes not only to high strength but also to high intrinsic toughness observed in this LPSO structure.