Self-diffusion of Fe in iron-aluminides studied by tracer and Mossbauer techniques

Self-diffusion of Fe-59 has been investigated in intermetallic phases of the FeAl-system at 26.5, 34 and 50 at.% Al. The combination of traditional grinder and sputter techniques for serial sectioning permitted to cover a fairly wide diffusivity/temperature range in our measurements. Fe diffusion in Fe73.5Al26.5 has been measured from 724 - 1475 K, which includes the A2-B2 and B2-D0(3) order transition temperatures. At the critical temperatures the slope of the Arrhenius diagram changes and the activation enthalpy is larger for the low-temperature phase. Fe diffusion in Fe66Al34 and Fe50Al50 is characterized by linear Arrhenius diagrams. Quasielastic Mossbauer spectroscopy (QMS) indicates that the Fe atoms jump into antistructure sites on the Al-sublattice and back to the Fe-sublattice. The time fraction during which the Fe atoms occupy antistructure sites increases with increasing Fe content and temperature. Close to stoichiometry this fraction is small.