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

Highlights: • Microstructural evolution of Cu–Ni–Si power mixture is investigated systemically. • A schematic diagram of reaction process of Cu–Ni–Si power mixture is proposed. • Basic knowledge can be obtained for regulating microstructure and properties of Cu–Ni–Si alloys. • Ni and Si content of Cu–Ni–Si alloys is hope to be enlarged and thus improve strength. 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.