Microstructure evolution and mechanical property of Cu-15Ni-8Sn-0.2Nb alloy during aging treatment

• The precipitation sequence with aging time was characterized in detail. • DO 22 is present in the Ni-poor region while L1 2 appears in the Ni-rich region. • The coexistence of DO 22 and L1 2 results in the peak hardness of alloy. • DO 22 and L1 2 can appear simultaneously in different regions of modulated structure. Aging treatment of Cu-based alloys is essential to enhance their strength that is desirable for their extensive engineering applications in electrical industry, whereas the underlying mechanism of strengthening is essential for massive manufacturing of these alloys. Here, the microstructure evolution of a supersaturated solid solution Cu-15Ni-8Sn-0.2Nb alloy aged at 400 °C for different time was characterized at atomic scale using state-of-the-art transmission electron microscopy (TEM) and the corresponding mechanical property was also measured. The results reveal that the modulated structure, DO 22 /L1 2 ordering, and discontinuous precipitation (DP) appeared in the advances of aging time. At the early stage of aging treatment, component modulation waves and satellite spots appeared from spinodal decomposition and the modulation wavelength was identified in the range of 1–7 nm. Subsequently the modulated structures formed -poor-rich solute regions, of which DO 22 ordering was present in the Ni-poor region while L1 2 ordering appeared in the Ni-rich region. The sequence of ordering precipitates was further verified by density functional theory (DFT) simulations. Furthermore, orientation relationships and interfacial structures between DO 22 , L1 2 phases and the parent matrix were determined. The measured hardness of alloy reached a maximum value of 335 HV after aging for 120 min due to the coherence between the two ordering phases and matrix. These results illustrated the importance of aging on structural evolution and mechanical property of Cu-15Ni-8Sn alloy at various heat treatment stages, which could potentially help in manufacturing promising alloys for their extensive engineering applications.