Non-Schmid response of Fe₃Al: The twin-antitwin slip asymmetry and non-glide shear stress effects

The non-Schmid effects in DO₃ ordered Fe₃Al (DO₃-Fe₃Al) are investigated by utilizing experimental measurements of the onset of slip and atomistic scale simulations to study slip directionality and core effects. Uniaxial tension and compression experiments were conducted on DO₃-Fe₃Al single crystals utilizing high resolution Digital Image Correlation (DIC) to measure local slip strain evolution. The measured critical resolved shear stress (CRSS) values exhibited close agreement with the theoretical values upon developing a modified Peierls-Nabarro (P-N) formalism relying on molecular dynamics (MD) simulation results. Both experimental and theoretical values indicate the break-down of Schmid Law due to two factors: the role of non-glide shear (NGS) stress component acting on the glide plane, called the NGS effect, and twinning-antitwinning asymmetry, termed the TA effect. To ascertain the role of NGS stress component on the dislocation core structures, molecular statics (MS) simulations were conducted upon imposing elastic-anisotropic dislocation displacement fields with Eshelby-Stroh formalism. Both experimental measurements and modified P-N calculations confirm that the applied NGS stress component is as important as TA slip asymmetry on the break-down of Schmid Law in CRSS values. The calculated core spreading suggests that the extent of the relative displacements on {110} family planes, favoring either twinning or antitwinning shear, can significantly contribute to the non-Schmid behavior of DO₃-Fe₃Al with the accompanying elastic shear coupling between NGS stress component and glide shear (GS) strain. Further extension of the modified P-N formalism towards yielding behavior at continuum scale is also discussed.