Papers by Keyword: Emission Mössbauer Spectroscopy

Abstract: Grain boundary diffusion of Co in Mo has been studied by radiotracer analysis and emission Mössbauer spectroscopy. The experimental results are treated based on the specified Fisher model. The mechanism of grain boundary diffusion of Co in Mo and temperature dependences of segregation factor and grain boundary diffusivity have been determined.

Abstract: Capabilities of the emission nuclear gamma resonance (NGR) spectroscopy in studying grain boundaries in metals are considered. It is demonstrated that this method enables to evaluate grain-boundary segregation factors, to determine grain-boundary diffusion mechanisms, to estimate an effective diffusion coefficient in near-boundary areas, etc. Besides, this method permits to evaluate quantitatively differences in the properties of grain boundaries of polycrystalline and nanostructured materials.

Abstract: The possibilities of Fisher’s model development and generalization are considered, as this model in its classical form contradicts some experimental results. Particularly, it does not explain such a phenomenon, observed in Mössbauer studies, as the transfer of grain-boundary diffusing atoms into near-boundary crystallite areas at temperatures when the volume diffusion is admittedly frozen. Different models explaining this phenomenon are briefly reviewed, the greatest attention being paid to a model accounting for the presence of equilibrium-composition near-boundary layers. It is demonstrated that based on the results of grain boundaries investigations one can conclude that at relatively low temperatures (< 0.35 – 0.40 Tm) the diffusant pumping from a grain boundary proceeds much faster than volume diffusion, and possible reasons for that are considered.

Abstract: The results of NGR studies of grain boundaries in nanocrystalline metals are briefly reviewed and analyzed together with the data of ordinary diffusion experiments. Grain boundaries in materials obtained both by powder technologies and severe plastic deformation (SPD) are considered. Possible factors causing accelerated mass transfer in every case are analyzed with the account taken of specific features of the structure of these materials.

Abstract: The properties of grain boundary cores and adjacent areas in polycrystalline Nb manufactured by rolling with subsequent recrystallization annealing and nanocrystalline Nb obtained by high pressure torsion have been investigated by the Mössbauer emission spectroscopy on 119mSn nuclei.

Abstract: Possibilities of grain-boundary diffusion and segregation studies using nuclear gammaresonance spectroscopy (NGR) are considered. It is shown that the results of the Mössbauer investigations testify the necessity to specify the classical Fisher’s model of grain-boundary diffusion, and a possible way of such specification is suggested. It is demonstrated that investigation of grain boundaries using emission Mössbauer spectroscopy appreciably supplement the information obtained from the diffusion profiles analysis. In particular, Mössbauer investigations make it possible to evaluate directly the grain-boundary segregation factor, to determine the grain-boundary diffusion mechanism, to estimate the rate of the diffusant pumping from a grain boundary core into the bulk, etc.