Controlled nanoscale intermetallic layer engineering enables ultrahigh interfacial strength–ductility synergy in maraging steel/Nb/high-entropy alloy composites

Interfacial reaction-induced intermetallic compounds (IMCs) are brittle and prone to triggering cracking, severely deteriorating the mechanical performance of composite interfaces. Overcoming IMC-induced embrittlement remains a longstanding challenge in interface design. Here, we counterintuitively leverage IMCs by inducing their nanocrystallization to achieve ultrahigh interfacial strength–ductility synergy in 18Ni350/Nb/AlNbTi₃Zr_1.5 composites. Specifically, a uniform and continuous nanostructured C14-type Fe₂Nb interfacial reactive layer (IRL) is engineered at the 18Ni350/Nb interface through the in situ nanoscale reaction. In contrast to the coarse-grained Fe₂Nb IRL characterized by pronounced brittleness, this well-developed nanocrystalline Fe₂Nb IRL exhibits superior strength and plasticity by activating grain rotation, stacking fault-mediated slip, and phase transformation-induced plasticity. These deformation mechanisms, originated from the nanostructuring and element doping of Fe₂Nb, promote stress relaxation, uniform deformation, and crack blunting during the deformation of the composite interface, thereby mitigating the brittleness of IMCs. Concurrently, the excellent thermodynamic inter-solubility of Ti, Zr, and Nb fosters robust metallic bonds without forming IMCs at the Nb/AlNbTi₃Zr_1.5 interface, which enhances compatible deformation by facilitating interfacial dislocation emission and movement, alleviating strain concentration, and preventing premature cracking during mechanical loading. Our findings reveal the significant potential of nanocrystallization engineering in overcoming the interfacial brittleness of IMCs and provide a new strategy for designing ultrahigh-strength dissimilar interfaces.