Investigation of the diffusion mechanism of 57Co atomic probes at the grain boundary core, segregation of 57Co at grain boundaries and measurement of the diffusion parameters of 57Co outside of the grain boundary core in polycrystals of Ta, W and Cr.

A new method [1-3] developed for the study of intercrystallite diffusion in polycrystals was used to obtain earlier unavailable information about regular features of this phenomenon and to measure earlier inaccessible parameters determining those regular features. The diffusion mechanism of the small radius atomic probe Co-57 in the grain boundary core of poly crystalline Ta and W is interstitial and in the grain boundary core of polycrystalline Cr is via vacancies. In poly-Cr and poly-W atomic probe Co-57 segregated at grain boundaries, but in poly-Ta it "antisegregated". In Poly-W the stationary region of high concentration of point defects disappear at low temperatures and cause new phenomena - the expansion of the region of high concentration of point defects localized near grain boundary.