Wire arc additive manufacturing of layered immiscible Cu-Fe bimetallic structures: Liquid-liquid phase separation and strengthening mechanisms

Periodically layered immiscible Cu-Fe bimetallic structures were fabricated by cold metal transfer-based wire arc additive manufacturing. The effects of heat input on the liquid-liquid phase separation behavior, interfacial microstructure, and mechanical properties were investigated. With increasing heat input, intensified liquid-liquid phase separation resulted in pronounced Fe segregation and honeycomb-like Fe-rich phases at the Cu-side frontier. It also caused interfacial microcracks induced by liquid Cu penetrating along Fe grain boundaries. Both matrices exhibit random textures with decreasing dislocation density; nanoprecipitates provide pinning. The sample with 5.5 m/min Cu feed rate shows optimal performance: 466.3 MPa strength, 8% elongation, sound bonding, necking/fracture in Cu, 13.4 %IACS conductivity. Properties stem from dislocation and precipitation strengthening; conductivity depends on solute Fe. Post-heat treatment increases elongation 30% and conductivity to 18.9 %IACS. This work shows that controlled liquid-liquid phase separation in layered immiscible systems offers an effective strategy for achieving excellent strength–conductivity combination in Cu-Fe bimetallic components.