Investigation of the mechanical response of single crystal magnesium considering slip and twin

Abstract

Abstract The mechanical response of hexagonal close-packed (HCP) materials are highly anisotropic due to the inherently asymmetric slip and twin systems in the HCP atomic structure. The slip and twin systems in the HCP atomic structure, i.e., slip/twin directions and planes, are not isotropic in terms of geometry. This inhomogeneous directionality produces various stress-strain responses along different loading directions. The question of which slip/twin systems are available in a specific HCP material has not been well understood and needs further experimental investigation. Since there was lack of experimental evidence that the pyramidal I slip is activated in single crystal magnesium, the pyramidal I slip has not been considered as the major slip mode in the computation research of single crystal magnesium. However, recent experimental and atomistic simulation works indicate that the pyramidal I slip is the dominant slip mode in the deformation of single crystal magnesium. Taking into account these recent findings on the pyramidal I slip in magnesium, this research aims to investigate the mechanical response of single crystal magnesium using the most number of slip/twin systems ever explored, including the pyramidal I slip system, tensile twin, compressive twin and etc. To quantify the contribution of each slip and twin system to overall deformation, i.e, the total shear strain amount, the plane strain compression experiment of single crystal magnesium performed by (Kelley and Hosford, 1967, 1968) is reproduced using crystal plasticity (CP) simulations. The computation scheme employed uses a standard crystal plasticity framework that takes into account the slip process and has an additional feature to implement the twinning process. Findings from the CP simulations indicate that the contribution of the pyramidal I slip mode to the overall shear strain in the deformation of single crystal magnesium is significant and comparable to that of the pyramidal II slip mode if their CRSS (Critical Resolved Shear Stress) are of similar magnitudes. The findings indicate as well that the pyramidal I slip mode will be dominant over pyramidal II in real experiments since the CRSS of pyramidal I has been reported to be smaller than that of pyramidal II by the recent experimental and atomistic simulation researches.