Composition formulas of Cu-Ni industrial alloy specifications

It was recently known that the compositions of industrial alloy specifications generally satisfy simple composition formulas issued from short-range-order structural units in their basic solid solutions. In present work, Cu-Ni face-centered-cubic alloys were further addressed by introducing the cluster-plus-glue-atom model for the short-range-order structural descriptions. Composition formulas covering only the first twelve and the second six neighbor shells in the face-centered-cubic lattice are proposed, [Cu-Cu12](Cu,Ni)6 for the Cu-rich alloys and [Ni-Ni12]Cu6 ~ [Ni-Ni12](Cu5Ni) for Monel alloy, the only Ni-rich alloy specficiation, where the square-bracketed part represents a cuboctahedral cluster. The alloy specification selection is also discussed in terms of valence electron numbers per unit formula. The present work confirms that well-established industrial alloys have simple composition rules that reflect the intrinsic short-range-order local structures in the solid solutions.