The concentration dependence of the interdiffusion coefficient was measured, by means of electron probe microanalysis, at 7 temperatures. The concentrations, of 6 to 16at%Si, were near to the concentration of the A2-B2 ordering transition. In the case of the ordered B2 phase, the interdiffusion coefficient was some 2 to 3 times lower than that in the disordered phase. When near to the B2 ordering transition, the diffusion coefficient depended strongly upon the Si concentration. It was found that there was a maximum in each diffusion coefficient versus concentration plot. This was shifted, by about 2 to 3% to the left, from the ordering transition concentration. This behavior was explained in terms of a concentration dependence of the thermodynamic factor. The dependence of the thermodynamic factor upon temperature and concentration was calculated within the framework of the mean field theory, and the fluctuation contribution was estimated by using a scaling hypothesis. The calculated dependences were in good agreement with experimental data.

E.Rabkin, B.Straumal, V.Semenov, W.Gust, B.Predel: Acta Metallurgica et Materialia, 1995, 43[8], 3075-83