Diffusion in the D03-type intermetallic phase Fe3Si

Abstract

The diffusion of Fe and Ge in the D0₃ phase Fe₃Si has been studied as a function of temperature and composition using a tracer sectioning technique and the radioisotopes ⁵⁹Fe and ⁷¹Ge. One experiment with the short-lived ³¹Si radiotracer was carried out to examine the similarity of Ge diffusion and Si diffusion. These elements diffuse with similar rates. The results are discussed considering composition dependences, magnetic and ordering transitions. The most striking fact is that Fe diffusion in the D0₃ structure Fe₃Si is much faster and the corresponding activation enthalpy is considerably lower than in bcc Fe or in disordered Fe-rich Fe-Si alloys. By contrast, diffusion of Ge and Si is a great deal slower and the activation enthalpy is higher than in the disordered phases. While Fe diffusion is strongly dependent on the alloy composition, diffusion of Ge in Fe₃Si is less affected by the Si content. Possible diffusion mechanisms are discussed in the light of additional information on Fe₃Si. The main conclusions for Fe atoms are that diffusion occurs by nearest-neighbour jumps on the Fe sublattice; and that it is mediated by thermal vacancies which are present in high concentrations.