Interface-dependent dynamic deformation behavior in FCC/BCC high-entropy alloy nanolaminates

Abstract

Dual-phase high-entropy alloys (DP-HEAs), characterized by an alternation of soft and hard phases, are expected as promising candidates for structural applications, owing to their remarkable combination of high strength and ductility. However, the role of phase interfaces in the dynamic deformation of these nano lamellar systems remains poorly elucidated, primarily because of the challenges pertinent to real-time characterization at nanoscopic resolutions. Here, the intricate interplay between shock waves and phase interfaces in face/body-centered cubic (FCC/BCC) FeCoNiCu_xAl_1-x HEA nanolaminates was examined, through performing large-scale molecular dynamics (MD) simulations. As a consequence of stress concentration at interfaces, shock waves with intensities beneath the Hugoniot elastic limit (HEL) were confirmed to trigger dislocation at these interface sites. These dislocations slipped in directions counter to that of deformation-induced ones, making them susceptible to collisions and subsequent dislocation reactions, which effectively fostered the emergence of immobile Hirth dislocations and thus an additional strain-hardening effect. Meanwhile, the BCC phase was demonstrated to undergo deformation through a transformation into a hexagonal close-packed (HCP) structure upon exposure to shock waves, accompanied by twinning within emergent HCP lamellae. This would contribute to dissipating energy from the propagating shock waves. More interestingly, the magnitude of both phase transition and twinning can be dynamically manipulated through the strategic manipulation of Cu/Al compositional ratios in the BCC phase. In addition, the layer-thickness difference was corroborated to dramatically affect the dynamic deformation behavior of DP-HEA systems. A decrease in layer thickness allowed a more frequent interaction between shock waves and phase interfaces, alleviating stress concentration and encouraging greater plastic deformation. Our current study illuminates the dynamic deformation characteristics of DP-HEAs, offering pivotal insights that can design and develop HEAs with optimized properties for future applications.