Hierarchical Interfacial Heterogeneity and Plastic Bridging Activate Dislocation Accommodation in Fe-Al Composites

Achieving ultrahigh interfacial bonding in Fe-Al composites remains challenging because brittle intermetallic compounds (IMCs) formed at reactive interfaces typically exhibit sluggish dislocation kinetics, which undermines load transfer, especially when the IMC layer becomes thick. Here, a Fe-Al composite with dislocation-activated interfaces is reported to overcome the strength degradation commonly associated with thick IMC layers by in situ architecting hierarchical IMC heterogeneities together with a B2-ordered plastic bridging layer at the interface. Despite an IMC thickness of 19.4 µm, the composite delivers an interfacial fracture toughness of 22.6 MPa·m^1/2 and an interfacial strength of ∼202.4 MPa, about fivefold higher than reported FACs with comparable IMC thickness. The exceptional interfacial strength originates from a multilevel cooperative strengthening-toughening mechanism enabled by the tailored interfacial architecture: chemical heterogeneity and Al₁₃(Co, Ni)₄/Al₉(Co, Ni)₂ heterogeneous IMC architecture promote load sharing and strain delocalization, while the B2 buffering layer facilitates dislocation slip and stable interfacial accommodation. Moreover, amorphization within Al₉(Co, Ni)₂ triggered by interfacial failure provides an additional energy-dissipation pathway that suppresses catastrophic shear localization. This work highlights an interfacial-architecture strategy for activating dislocation accommodation in IMCs and improving damage tolerance in bimetallic composites.