Architecting Ta-V-enriched local chemical ordering for strength-ductility synergy in multi-principal element alloys

Local chemical ordering (LCO) is a key microstructural feature in multi-principal element alloys (MPEAs), critically influencing their mechanical properties. However, the mechanisms of LCO formation and their interactions with dislocations remain unclear, and effective strategies for architecting LCOs to enhance both strength and ductility are lacking. In this work, we achieve controlled formation of novel Ta-V-enriched LCOs within a Ti-Zr-Nb-Ta-V alloy system, and investigate their formation mechanisms and interactions with dislocations through a combination of experimental characterization, thermodynamic calculations, and molecular dynamics simulations. Our results reveal that these LCOs, which act as precursors to the C15 Laves phase, exhibit two distinct morphologies: string-like and cluster-like, whose prevalence depends on V content. Mobile dislocations interact with string-like and cluster-like LCOs via shearing and bypassing mechanisms, respectively. Cluster-like LCOs provide stronger and more sustainable barriers to dislocation motion than their string-like counterparts. Importantly, they not only strengthen the matrix by impeding dislocation motion but also enhance ductility by promoting dislocation multiplication and activating multiple slip systems. Dislocation loops generated by interactions with cluster-like LCOs act as Frank-Read sources, expanding during deformation to facilitate further activity. Consequently, the V15 alloy, rich in cluster-like LCOs, exhibits synergistic mechanical improvements over the V5 alloy, achieving a yield strength of 1.04 GPa, ultimate tensile strength of 1.2 GPa, and ductility of 20.6 %. This work provides fundamental insights into LCO-driven deformation mechanisms and opens a pathway for designing high-performance MPEAs through precise LCO control.