The thermal instability mechanism and annealed behavior of ultra-high strength Cu-Ni-Sn alloy

In the aging process of the Cu-Ni-Sn alloy, various precipitate transformations can be observed in detail. The peak-aged alloy is strengthened by the DO₂₂ ordered structure, while in the over-aged alloy, the precipitates are completely transformed into discontinuous precipitates. In this study, the Cu-9Ni-6Sn alloys aged for different times were subjected to severe plastic deformation to obtain two types of Cu-9Ni-6Sn alloy wires: peak-aged strengthening (S1) and over-aged strengthening (S2). S1 wires exhibit higher tensile strength and lower electrical conductivity, up to 1385 MPa, 11.1 %IACS, while S2 has lower strength and higher electrical conductivity, about 1178 MPa, 25.0 %IACS. The softening temperature of the S2 wire is around 400°C, which is better than the 300°C of the S1 wire. The decrease in dislocation density and the growth of γ phases lead to the annealing softening of the two types of wires. Compared to S1 wires, the nanofibrous discontinuous precipitates in S2 wires can retard the spheroidization of precipitates and static recrystallization, thus hindering the occurrence of softening.