A model based on zonal dislocation walls for kink band formation in nano-layered HCP crystals

Abstract Kink bands (KBs) are localized regions that rotate relative to adjacent, undeformed areas. They typically form in crystalline materials characterized by strong structural anisotropy and limited slip activity, such as hexagonal close-packed (HCP) structures and particularly in high- c / a nano-layered HCP crystals such as MAX phases. KBs induces lattice rotation and reorients the structure to activate additional slip systems, aiding in meeting the von Mises criterion. In this work, we propose a new model for KB formation based on the concept of zonal dislocations (ZDs). Continuum-scale thermodynamic analyses demonstrate that this model is both physically plausible and structurally stable. These findings are corroborated by atomic-scale simulations, which confirm the feasibility of ZD formation and reveal its internal structure. This model provides a coherent framework for interpreting plasticity in MAX phases and offers a compelling explanation for the hysteresis often observed during deformation, an open question in their mechanical behavior. Our results show that the formation of a single wall of basal dislocations, followed by their dissociation into ZDs, is significantly more energetically favorable than existing models that rely on the formation of two opposing walls of dislocation dipoles, currently considered the dominant pathway for KB initiation.