Unveiling microstructural evolution and its effect on mechanical performance in a Cu-9Ni-6Sn alloy

Cu-9Ni-6Sn alloy exhibits profoundly potential as a new environmental-friendly conductive elastic material. In this work, the formation and growth mechanism of discontinuous precipitation, as well as its effect on mechanical properties of Cu-9Ni-6Sn alloy are systematically studied. The investigation indicated that the discontinuous precipitation does easily initiate from random grain boundaries but showing opposite result for Sigma 3 boundaries. The lower frequency Sigma 3 boundaries relatively, the more intense the solute diffusion, resulting in a higher volume fraction of discontinuous precipitation. The increasing aging temperature and time will accelerate the grain boundary discontinuous reaction, and the fine-grained samples exhibit a higher volume fraction of discontinuous precipitates and smaller lamellar spacing due to the more nucleation sites and increased interfacial energy. The strengthening mechanism of Cu-9Ni-6Sn alloy mainly focus on dislocation strengthening and precipitation strengthening, in which the D022 or L12-gamma ' phases exhibit more significantly precipitation strengthening effect but is difficult to guarantee ductility. The localized grain boundary discontinuous precipitation detrimentally affect both the tensile strength and ductility. But the nano-lamellar discontinuous precipitation is beneficial to the strength-ductility trade off when it occupies the entirely Cu matrix. This work establishes a robust foundation for the microstructural optimization and multi-component design of Cu-9Ni-6Sn alloy.