The Influence of Porous Structure on the Interdiffusion Kinetics of Cu-Ni System During Spark Plasma Sintering

The interdiffusion kinetics of Cu-Ni system and the influence of porous structure on atomic diffusion kinetics during spark plasma sintering (SPS) were investigated. The interdiffusion coefficient of the Cu-Ni system annealed under SPS is much higher than that without current when the temperature exceeds 700 °C. By comparing the interdiffusion behaviors between Ni powder/Cu foil interface and Ni foil/Cu foil interface, the interdiffusion rate at the foil/powder interface was found to be significantly higher than that at the foil/foil interface during SPS. The diffusion process at the Ni powder/Cu foil interface shows two clearly identified stages: a high diffusion rate at the initial stage with high porosity and a slower diffusion rate at the mid-late stage with low porosity. The diffusion coefficient at the initial stage is nearly 5.2 times higher than that of the mid-late stage, demonstrating that the diffusion rate at the foil/powder interface decreases with the gradual reduction of porosity during the SPS densification process. The porous structure leads to an extremely high local current density at the neck area, which results in a high density of crystal defects at the diffusion interface and subsequently accelerates atomic diffusion.