Activation volume for interdiffusion in bcc ordered and disordered phases of the Fe–Al system

Abstract

The activation volume for interdiffusion in bcc ordered and disordered phases of the Fe–Al system has been determined in the temperature range from 1173 to 1473 K by measuring the pressure dependence of the interdiffusion coefficient. in the concentration range from 10 to 20 at.% Al of the bcc disordered phase is found to have an almost constant value of (0.40–0.45)V 0 (V 0 is the molar volume of the alloys) against temperature, which corresponds to the lower limit for the monovacancy mechanism in bcc pure metals or random alloys. On the other hand, the value of in the B2 FeAl phase increases with increasing temperature from 0.60V 0, the upper limit for the monovacancy mechanism, to (0.80–0.90)V 0, suggesting that divacancies contribute substantially to the diffusion at higher temperatures and in the off-stoichiometric region.