Bulk and grain boundary diffusion of Co in Cu

•Diffusion profiles of Co in Cu were measured by EPMA at temperatures 600–800 °C.•The accelerated GBD was not observed.•It is shown that GB surface tension gradient leads to the retardation of GBD Co in Cu.

Co diffusion in Cu was studied by electron probe microanalysis (EPMA). The samples were annealed at the temperature range 600–800 °C (0.65–0.8Tm – Cu melting temperature). The Co concentration was measured along grain boundary (GB) in adjacent to GB region and far from it. It was shown that Co concentration does not depend on the distance from GB at the same depth. This result indicates the absence of the accelerated GB diffusion. The possible reasons for such unexpected result can be connected with the gradient of GB surface tension as the additional driving force for GB diffusion. The last effect is related the increasing of Cu GB surface tension on Co concentration.