Chemical synthesis and properties of nanocrystalline Cu–Fe–Ni alloys

The chemical reduction of Cu2+, Fe3+, and Ni2+ ions with sodium borohydride in aqueous solution followed by heat treatments at 300–900°C in a H2 atmosphere was investigated to obtain nanocrystalline Cu–Fe–Ni, which may have low thermal expansion and enhanced thermal and electrical conductivities. The samples were characterized by X-ray diffraction, optical microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, thermomechanical analysis, and electrical conductivity measurements. Thermal conductivity was estimated using the Wiedemann–Franz law. Sintering lead to the formation of a Cu-rich phase and a γ–(Fe, Ni) Invar phase. The growth and stability of the Cu and γ–(Fe, Ni) Invar phases and the effects of composition on the properties of Cu–Fe–Ni alloys were investigated.