Lattice reconstruction and dislocation recapture enhance the fracture resistance of η-Fe₂Al₅-bearing interfaces in dissimilar Al/steel joints

The inherent brittleness of interfacial Al-rich intermetallic compounds (IMCs) remains a major obstacle to reliable Fe-Al-based lightweight structural joints, as welding-induced residual-stress localization readily triggers crack initiation within the IMC-bearing region. Here, a two-step strategy integrating lattice reconstruction with dislocation recapture is proposed to improve the room-temperature fracture resistance of η-Fe₂Al₅ in dissimilar Al/steel joints. Low-temperature annealing promotes rapid reconstruction of the strained η-Fe₂Al₅ lattice and relieves long-range residual stress, while subsequent water quenching facilitates the recapture of dispersed isolated dislocations. The treated joints achieve a tensile strength of ~258.6 MPa, corresponding to an ~80.3% increase over the as-processed state, together with a ~70% increase in the fracture toughness of the η-Fe₂Al₅-bearing layer. In situ X-ray diffraction and first-principles calculations reveal that localized compressive strain accelerates the reverse eutectoid transformation, through which β₀-associated transformation strain provides an additional driving force for dislocation-network decoupling and stress relief of the η-Fe₂Al₅ layer. The retained coherent η-Fe₂Al₅/β₀ interface and the recaptured isolated dislocations further promote local strain accommodation in η-Fe₂Al₅, while crack deflection, blunting, and bridging dissipate fracture energy, as supported by molecular dynamics simulations. These results suggest a potential strategy for improving fracture-limited IMC-bearing interfaces in dissimilar-metal joints through coordinated regulation of residual stress and dislocation functionality.