Mechanical spectroscopy, positron annihilation spectroscopy, and the radiotracer diffusion technique (59Fe self-diffusion measurements) were applied to interpret anelastic relaxation effects caused by C atoms and vacancies in Fe3Al-based alloys with and without strong carbide forming elements (Ti and Nb). The decrease of the Snoek-type relaxation peak (denoted as S-peak) in the internal friction spectra of Fe–26Al–(2&4)Ti and Fe–26Al–0.3Nb alloys with respect to the S-peak in binary Fe–26Al alloy (all compositions in at%) was related to a decrease in the amount of interstitially dissolved C atoms. Kinetic aspects of the removal of C atoms from the solid solution were discussed with respect to the annealing temperature. The so-called X peak, which was observed in the internal friction spectra of Fe–26Al alloy, also almost disappears after alloying with Ti. The results indicate that the change in the content of interstitially dissolved C was the main reason for the observed changes of the S and X peak intensities. The effect of heat treatments on thermal vacancy concentration was evaluated by positron annihilation spectroscopy. A minor influence of the addition of Ti and Nb on the total concentration of vacancies was deduced from the positron annihilation and radiotracer diffusion studies.

Study of Atom Diffusivity and Related Relaxation Phenomena in Fe3Al–(Ti,Nb)–C Alloys. I.S.Golovin, S.V.Divinski, J.Čížek, I.Procházka, F.Stein: Acta Materialia, 2005, 53[9], 2581-94