Effect of Grain Boundary Misorientation on the Asymmetry, Anisotropy, and Nucleation Stresses of the {10-12} Twinning and Non-basal Slip in Magnesium

Baird, J., El Kadiri, H., Oppedal, A. L., Kapil, J., Ma, Q., & Vogel, S. C. (2012). Effect of Grain Boundary Misorientation on the Asymmetry, Anisotropy, and Nucleation Stresses of the {10-12} Twinning and Non-basal Slip in Magnesium. Proceedings of Mg2012: 9th International Conference on Magnesium Alloys and their applications. Vancouver, BC Canada.

Early reports pertaining to Non-Schmid phenomena of both slip and twinning in BCC and HCP structures and their effect on anisotropy and asymmetry were essentially attributed to either unusual activities of screw dislocations or to a certain solute effects on dislocation activity. In this study, we show an important asymmetry of the {10-12} twinning and non-basal slip stresses that depend on the initial texture. Crystal plasticity simulations and non-destructive EBSD suggested that these non-Schmid effects correlate with the effect of mantle plasticity, which changed with the nature of initial texture. The critical stresses for both of these deformation mechanisms were identified to change by at least a factor of two for different initial textures of the same material composition. Sharp [0002] fibers were revealed to cause softening of twinning and hardening of non-basal slip while axisymmetric textures hardened twinning and softened non-basal slip. While both non-basal slip and twinning correspond to extended and liberated partial dislocations, respectively, these reversed tendencies could not be explained unless slip and twinning are considered as mutually competitive mechanisms. As low misoriented grain boundaries harden slip, twinning becomes softer. Conventional crystal plasticity based on a pseudo-slip approach for twinning was unable to capture these mantle-induced textural effects related to the magnesium asymmetry.