Aging behavior of Cu–Ni–Si alloy

Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HREM) were employed to study the microstructure and transformation of Cu–Ni–Si alloy. In Cu–1.0Ni–0.25Si–0.1Zn (wt.%) alloy, the precipitate responsible for the age-hardening effect was the δ-Ni2Si originating in nucleation process. On aging at the temperature below ∼773 K in Cu–3.2Ni–0.75Si–0.3Zn (wt.%) alloy, there were three different transformation products: a modulated structure resulting from spinodal decomposition, a (Cu, Ni)3Si with DO22 ordering structure nucleating from the modulated structure, and a δ-Ni2Si phase with disc-like structure appearing in (Ni, Si)-rich regions. On aging at the temperature above ∼773 K, the transformation products were grain boundary and intragranular precipitations of δ-Ni2Si. The free energy versus composition curves were employed to further explain the experimental observations.