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 using cold metal transfer-based wire arc additive manufacturing. The effects of the heat input on the liquid-liquid phase separation behavior, interfacial microstructure, and mechanical properties were investigated in this study. An increasing heat input intensified liquid-liquid phase separation, resulting in pronounced Fe segregation and honeycomb-like Fe-rich phases at the Cu-side frontier, coupled with interfacial microcracking induced by liquid Cu penetrating along Fe grain boundaries. Both matrices exhibited random textures with decreasing dislocation densities, and the nanoprecipitates provided pinning. The 5.5 m/min Cu feed-rate sample exhibited optimal performance: 466.3 MPa strength, 8% elongation, sound bonding, necking/fracture in Cu, and 13.4%IACS conductivity. The properties stem from dislocation and precipitation strengthening, and the conductivity depends on the solute Fe concentration. Annealing at 600°C for 1 h increased elongation by 30% and electrical conductivity to 18.9%IACS. This study shows that controlled liquid-liquid phase separation in layered immiscible systems offers an effective strategy for achieving excellent strength–conductivity combinations in Cu–Fe bimetallic components.