Co Effect in the Precipitation Behavior in Cu-Ni-Si Alloy

Abstract

We investigated Co effect in precipitation behavior in Cu–Ni–Si alloy by analyzing the cohesive and interfacial energies of the second phase doped with Co based on the density functional theory (DFT) calculations. Co atoms are expected to reduce the cohesive energy of Ni₂Si, but increase the interfacial energy between Cu and Ni₂Si, resulting in the increment of the activation energy of Ni₂Si precipitation. Higher activation energy of (Ni,Co)₂Si precipitation leads a higher aging temperature or a longer aging time for precipitation compared to Cu–Ni–Si alloy. The experimental results and DFT calculation have a good agreement. And the DFT calculations predict that aspect ratio of (Ni₁–_x,Co_x)₂Si precipitates decreases according to Co concentration. Besides, experiments show that the precipitates in Cu–Ni–Co–Si alloy changed to a more spherical shape not only in the matrix but also at the grain boundary.