The influence of small amounts of interstitial solute atoms on the determination of the activation energies for self-diffusion and vacancy formation in α-iron

The influence of the interaction between vacancies and interstitial solute atoms (carbon and nitrogen) on the determination of the activation energies for self-diffusion and vacancy formation is investigated for the case of α-iron. It is shown that the value of the self-diffusion energy is not affected by the presence of interstitial impurities in the 1 to 10 at ppm range. The result for the vacancy formation energy (E) depends on the value of the binding energy of the interstitial solute–vacancy pair (EB). Since EB is correlated with the value of the vacancy migration energy (E), the result can be stated as follows: if E = 1.3 eV (low EB), E can be determined without taking into account the presence of 1 to 10 at ppm of interstitial impurities; if however E = 0.55 eV (high EB), this amount of interstitial impurities cannot be neglected in the determination of E. An important implication on the controversial problem of the vacancy migration energy is discussed.