The mechanism of superior strength-ductility synergy in ultrafine-grained (FeCoNiV)93Al7 dual-phase high-entropy alloy via in-situ techniques

Dual-phase high-entropy alloys (HEAs), characterized by a soft matrix and hard reinforcing phase, hold promise for exceptional mechanical properties, yet struggle to balance strength and plasticity due to the reinforcing phases enhancing strength while significantly reducing ductility. In this study, we engineered the coupling of ordered and heterogeneous structures within an ultrafine-grained dual-phase (FeCoNiV)₉₃Al₇ HEA, resulting in an outstanding synergy of strength and ductility, with a yield strength of 1260 MPa, ultimate tensile strength of 1651 MPa, and elongation of 18%. Employing advanced in-situ techniques (electron backscatter diffraction, digital image correlation, and synchrotron X-ray diffraction), we systematically investigated the deformation mechanisms. Our findings demonstrate that the mechanical properties are governed by a complex interplay of ordering treatment, grain size, phase volume fraction, and phase morphology. In the initial deformation stage, the yielding of the L1₂ phase triggers stress relaxation and subsequent stress transfer to the harder B2 phase, which significantly enhances yield strength and work-hardening rate. Notably, the L1₂ phase in this alloy exhibits exceptional work hardening capability, but as strain increased, load progressively transferred to the initially softer yet strain-hardening L1₂ phase. The dynamic stress redistribution between the two phases effectively retards the onset of alloy failure. To optimize mechanical performance, maintaining a moderate B2 phase volume fraction and minimizing coarse B2 grains through processing techniques is critical. This in-depth understanding of deformation and fracture mechanisms in dual-phase HEAs provides valuable insights for advancing alloy design and optimization strategies.