Grain boundary phase transformation in Cu–Co solid solutions

► Creep activation energy of pure copper was obtained. ► Creep activation energy of Cu–20at.% Ni foil was measured. ► Creep behavior of Co solid solutions in Cu was investigated. ► Activation energy at low temperatures increases with Co concentration by straight line. ► Activation energy at high temperatures depends nonlinear on Co concentration. The present work examined the creep behavior of copper based solid solutions with cobalt at temperatures between 980°C and 1080°C and stresses lower than 0.2MPa. The samples were made from 18μm foil and were formed into cylinders. After the pre-annealing at 1000°C during about 30h the samples had a parquet structure. The experiments were performed in the hydrogen atmosphere. New equipment was designed for these measurements. The activation energy of pure copper creep was close to the activation energy of copper volume self-diffusion. Cu–Co solid solution creep rate was always lower than that of pure copper. It was shown that the creep activation energy in the relatively low temperature region was higher than in the high temperature region. The same behavior was typical for all studied solid solutions. The transition temperature was about 1030°C. It was proposed that such creep behavior was connected with grain boundary phase transformation and explanation was made in terms of interface controlled diffusional creep.