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

ABSTRACT 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 Al 13 (Co, Ni) 4 /Al 9 (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 Al 9 (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.