Microstructure evolution and reaction behavior of Cu–Ni–Si powder system under solid-state sintering

Cu–Ni–Si powder compacts were firstly prepared by mechanical mixing and cold-pressing, and then held at 600, 700, 800, 900, 950 and 1000 °C for 5 min followed by water-quenching. Subsequently, X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and transmission electron microscope (TEM) were used to characterize the microstructure and phase composition of water-quenched samples, and competitive reactions among Ni–Si compounds were also discussed. Finally, a schematic diagram about the solid-state reaction process of Cu–Ni–Si powder system was proposed. Results showed that Ni and Si substances started to diffuse and reacted when the temperature was above 600 °C, resulting in the formations of Ni31Si12 phase at the primary powder boundary and Ni2Si precipitations inside the Cu powder, respectively. With the increase of temperature, Ni2Si phase dissolved into Cu matrix while the amount and size of Ni31Si12 phase increased along with the morphology changing from chrysanthemum-like shape to equiaxed structure. The final microstructure of Cu–Ni–Si powder system after sintering and water quenching consisted of Cu(Ni,Si) solid solution and equiaxed Ni31Si12 phase at the primary powder boundary, which was expected to achieve a combination of high strength and high electrical conductivity by subsequent heat treatments.