Precipitation strengthening of Cu-Ni-Si-based alloys: Experimental and computational insights

The effects of interfacial energy on precipitation behavior and physical properties of Cu-Ni-Si-(Co) alloys were investigated. The Cu-1.3Ni-0.3Si and Cu-1.3Ni-0.6Si-1.0Co alloys (in weight %) were prepared by combined cold-rolling and aging processes. The addition of Co promoted the formation of (Ni,Co)2Si by replacing Ni with Co in Ni2Si. Ab initio calculations demonstrated that the small addition of Co considerably reduced the interfacial energy between the Cu matrix and (Ni,Co)2Si, which effectively decreased the activation energy for precipitation. As a result, the precipitation of fine rod-shaped (Ni,Co)2Si was accelerated during the aging process and the number density of the precipitates increased up to 9.0 x 1010 cm-2. The nano-scale (Ni,Co)2Si precipitates with an average size of 13.5 nm strengthened the alloy properly through the Orowan mechanism without much loss of electrical conductivity. The maximum hardness and electrical conductivity were 220 Hv and 51 % International Annealed Copper Standard, respectively, for the Cu-1.3Ni-0.6Si-1.0Co alloy aged for 4 h at 420 degrees C.