Engineering core–shell architectures in gas-atomized Cu–Co–X (Si, V, Nb, Mo) based on CALPHAD-directed liquid–liquid separation

Cu-based contact materials for relays must preserve a continuous Cu pathway while resisting welding and erosion. Immiscible Cu–Co–X (X = Si, V, Nb, Mo) alloys provide a route to architected powders in which phase topology can be tailored during rapid solidification. We adopt a compute-before-make strategy that couples CALculation of PHAse Diagram (CALPHAD) vertical sections and equilibrium liquid-fraction trajectories with gas atomization, microstructural verification, and differential scanning calorimetry (DSC). Thermodynamic maps are first used to identify compositions with robust two-liquid windows (L → L 1 + L 2 ) and asymmetric liquid fractions favorable for core–shell or multi-core/shell architectures. Guided by this screen, four alloys—Cu45Co45Si10, Cu46Co46V8, Cu47Co47Nb8, and Cu47Co47Mo6 (wt%)—were processed by gas atomization and hot pressing. Secondary electron image/backscattered electron image imaging and electron probe microanalysis mapping reveal three reproducible topologies—irregular non-core–shell, core–shell, and multi-core/shell—with complementary partitioning of Cu to the matrix and Co + X to the dispersed phase that largely survives consolidation. DSC shows distinct thermal events between ∼1000 °C and 1400 °C; the sequence and temperatures align with calculated liquidus and L ↔ L 1 + L 2 onsets, thereby supporting the CALPHAD-guided thermodynamic screening. The measured characteristic temperatures define practical superheat and consolidation ranges that favor retention of the targeted topology while avoiding intermetallic regimes. The results establish a traceable CALPHAD-guided design–processing–validation pathway for Cu-based immiscible powders relevant to relay applications.