Mössbauer Investigation of Sn Diffusion and Segregation in Grain Boundaries of Polycrystalline Nb

The parameters of nuclear y resonance (Mossbauer) spectra on 119mnSn nuclei inserted into grain boundaries of polycrystalline Nb have been determined at the annealing temperatures of 680 to 994 K [0.25-0.36 melting temperature (Tm)]. Two components are observed in the nuclear emission gamma resonance spectra at all of the annealing temperatures considered. One of them (component 1) is suggested to result from the 119mSn atomic probes localized in grain boundary cores, while the other one (component 2) corresponds to that located in the near-boundary areas. Diffusion annealing temperature dependences of both components parameters have been analyzed. The coefficients and enthalpy of Sn grain-boundary segregation are determined based on this analysis, as well as the ratio of the diffusion pumping zone extension to the grain boundary width and the enthalpy of the atomic probes "pumping" from grain boundaries into the bulk.