Synergistic strengthening via reduced phase property mismatch in a dual-phase high-entropy alloy enabled by bidirectional precipitation engineering

Dual-phase high-entropy alloys (HEAs) have attracted considerable interest due to their combination of good ductility from the face-centered cubic (FCC) phase and high strength from the body-centered cubic (BCC) phase. However, their practical application is hindered by the strength–ductility trade-off. Here, we develop an integrated “directional solidification + aging treatment” strategy for an Al_1.25CoCrFeNi_2.8Mo_0.2 HEA, achieving an aligned FCC/L1₂ + BCC matrix/precipitate dual-phase structure strengthened by dual nanoprecipitates. This multiscale architecture promotes the precipitation of dense coherent L1₂ nanoparticles in the FCC matrix and significantly refines precipitates in the BCC matrix, reducing their average size from ∼73.5 nm to ∼24.9 nm. This unique “bidirectional nano-regulation” strategy - namely the synchronous nanostructural optimization in both FCC and BCC phases - results in a remarkable 40% increa4se in yield strength and a 20% enhancement in tensile strength, while fully retaining ductility. The synergistic mechanical performance is attributed to two underlying mechanisms: (1) the L1₂ nanoprecipitates in the FCC phase strengthen the matrix and enhance strain hardening capability through order strengthening and back-stress effects; (2) the refined precipitates within the BCC phase improve ductility by facilitating dislocation glide and mitigating stress concentration. Importantly, the aging treatment substantially reduces the nano-hardness difference between the two phases from 1.66 GPa to 0.62 GPa, which fundamentally enhances the deformation compatibility and suppresses strain localization. This study demonstrates that multiscale structural design aimed at minimizing phase property mismatch offers an effective pathway to transcend the conventional strength-ductility trade-off, thereby establishing new principles for the design of advanced heterostructured materials.