Interpretation of the anomalies of transition metal impurity diffusion in aluminium

Abstract

Experimental data and theoretical models have been used to show that impurity diffusion of transition metals in aluminium crystals at high temperatures is sensitive to structure. The transition metal impurity diffusion can proceed not only with normal characteristics, close to those of Al-self-diffusion, but also with anomalously high or anomalously low characteristics (namely, the activation energy and the frequency factor of the diffusion coefficient), which correspond to anomalously low values of the diffusion coefficient. Through phenomenological consideration of the diffusion equation an expression for the effective diffusion coefficient of crystals with dislocations decorated by impurity segregations has been obtained, which makes it possible to describe the characteristics and the conditions of the anomalous diffusion process. By treating the experimental data on diffusion of Fe in Al, using the model developed, the authors have inferred characteristics and peculiarities of the structure of the near-dislocation segregation regions and atomic mechanisms of the diffusion with anomalously high and anomalously low characteristics.