Compositional interpretation of high elasticity Cu–Ni–Sn alloys using cluster-plus-glue-atom model

The D022 or L12-γ′ phase strengthened Cu–Ni–Sn alloys possesses a characteristic microstructure, exhibiting the distribution of precipitated phase with smaller size on a spinodal decomposition structure, which leads to that the composition of the precipitated phase and Cu matrix cannot be precisely measured and restriction of the accurate compositional design of the alloys. The present work initials to introduce the cluster-plus-glue-atom model for compositional interpretation of the industrial Cu–Ni–Sn alloys, and then optimizing the cluster formula according to the measured composition of the relevant precipitated phases. Moreover, the solid solution content of Ni or the precipitation content of Sn are calculated based on the optimized cluster formula, and establishing the relationship between the alloy composition and properties. It indicates that the strength mainly relays on the precipitation content of Sn while the conductivity depends on the solid solution content of Ni, which is also suitable for the Cu–Ni–Sn–Zn (Co) alloys or Cu–Ni–Al alloys with similar characteristics. Additionally, the ratio of strength/resistivity increases in the alloys as the increasing Sn content under the premise of close to 3 of Ni/Sn (or (Ni + Co)/Sn) atomic ratio, but the discontinuous precipitation is easily to generate. Therefore, the improved properties of the alloys cannot be attained via the reducing ratio of Ni/Sn (or (Ni + Co)/Sn) atomic ratio solely. Based on the above, this work provides theoretical support and application methods for the compositional design and performance prediction of coherent D022 or L12-γ′ phase strengthened alloys.