Room-temperature diffusion of 63Ni, in Cu with a gradient microstructure prepared by surface mechanical attrition treatment, was investigated by using the radiotracer technique. The results revealed significant penetration of Ni into the nanostructured layer. The relevant diffusivity was higher, than that along the conventional high-angle grain boundaries, by about six orders of magnitude. This behavior was associated with a higher energy state of internal interfaces produced via plastic deformation. The diffusivity in the top surface layer was somewhat smaller than that in the sub-surface layer. This fact was related to nanotwin formation in the former during surface mechanical attrition treatment.

Toward the Existence of Ultrafast Diffusion Paths in Cu with a Gradient Microstructure - Room Temperature Diffusion of Ni. Z.B.Wang, K.Lu, G.Wilde, S.Divinski: Applied Physics Letters, 2008, 93[13], 131904