Segregation of 57Co Atomic Probes in the Cores of Grain Boundaries in d-Transition Metals

A new method, which has been developed to examine the structure and physical properties of cores of grain boundaries (GB's) (S.M. Klotsman, Sov. Phys. Uspech. 33, 55 (1990); V.N. Kaigorodov and S.M. Klotsman, Phys. Rev. B 49 (1994)), was used to study segregats localized in two discrete regions of polycrystals: cores of GB's and two-dimensional regions of the lattice adjacent to the GB's. This paper reports and discusses results of investigations of segregation of 57Co atomic probes in cores of GB's in the d-transition metals Cr, Ta and W. The interaction of 57Co AP's with GB's cores in metals is similar to their interaction with vacancies, because GB's cores are characterized, as vacancies in metals, by an excess volume and a negative charge. GB's are enriched with 57Co in chromium and tungsten. The activation enthalpy of the 57Co atomic probes segregation at GB's in Cr and W is proportional tothe local magnetic moment of 57Co atomic probes. GB's cores are found to be depleted of 57Co atomic probes in Ta.