Diffusion of Co, Mn, Ni, and Cr was studied in the intermetallic phase Fe 3 Al. The radiotracer method in combination with serial-sectioning has been used for diffusion profile determination. Wide temperature ranges were covered including the A2 and B2 phase fields of Fe 3 Al. The Arrhenius plots show only a small influence of the A2 B2 phase transition on the diffusivity. The results are discussed together with previous results from our laboratory on selfdiffusion in the Fe-Al system, which concerns self-diffusion of iron and the Al substitutes Zn and In. Solutes, which substitute primarily on the Fe sublattice of the B2 structure (Ni, Co) are slower diffusers than solutes, which substitute on the Al sublattice (Zn, In, Cr, Mn).
Self-diffusion of nickel and manganese has been investigated by the radiotracer technique in Ni50Mn50 alloys over a wide temperature range. Experiments were performed on disordered fcc, B2 and L10 structure phases present in the equiatomic alloy at high, intermediate, and low temperatures, respectively. The diffusivity of manganese was found to be significantly faster (factor 3 to 5) than that of nickel in the fcc and B2 phases. More than one order of magnitude diffusivity increase was observed upon the transition from the higher temperature fcc to the intermediate temperature B2 phase. The activation enthalpy from nickel self-diffusion in the disordered fcc phase is significantly higher than the corresponding value for manganese. In the B2 phase there is only a slight difference between the activation enthalpies of the components, which indicates a coupled diffusion mechanism of the two components. A comparison of the present tracer self-diffusion data with literature data on interdiffusion in the Ni-Mn system permits to estimate thermodynamic factors by using the Darken-Manning equation. The thermodynamic factor varies from 3 to 5 depending on the structure.
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