Highly corrosion-resistant Cu70(Ni,Fe,Mn,Cr)30 cupronickel designed using a cluster model for stable solid solutions

Minor M (M = Fe, Mn, Cr) additions are widely added to enhance the corrosion resistance of commercial cupronickel alloys. The present paper aims at optimizing the amounts of M in Cu70(Ni,Fe,Mn,Cr)30 (at.%) alloys using a cluster-plus-glue-atom model for stable solid solutions. By this model, it assumed that 1 M atom and 12 Ni atoms formed an M-centered and Ni-surrounded cube-octahedron cluster and the isolated M1Ni12 clusters are embedded in a Cu matrix, conforming to a cluster formula [M1Ni12]Cu30.3 = [M1/13Ni12/13]30Cu70. A structure of this kind satisfies ideally the nearest neighbor requirement, i.e. only M–Ni and Ni–Cu neighbors are allowed and the unfavorable Cu–M pairs are avoided, and hence it describes a stable solid solution structure with good thermal stability. Electrochemical corrosion measurements indicated that [(Fe0.6Mn0.25Cr0.15)1Ni12]Cu30.3 had the best corrosion resistance in 3.5% NaCl aqueous solution.