Relaxation resulting from atomic defects in quenched Fe-Al alloys

Two relaxational internal friction peaks in quenched Fe-Al alloys with different Al content have been investigated using a computer-controlled automatic inverted torsion pendulum through free-decay and forced vibration method. It has been shown that the two peaks (P1, 180℃ and P2, 340℃) appear only in the heating process and do not appear in subsequent in-situ cooling process. It is suggested that P1 resulted from the stress-induced reorientation of di-vacancies, which consists of the reorientation of nearest neighbour Fe-vacancies on the α and β (or γ) sublattice sites. The relaxation strength of P1 varies im-monotonicly with Al content and there is a maximum at about 25% Al(atomic percent). There is no P1 peak in the Fe-Al alloys with lower Al content since vacancies exist in the form of isolated vacancies. When Al content is over 25%, the number of vacancies on β and γ sites is reduced. Therefore, the nearest neighbour di-vacancies are decreased and the height of P1 peak declines. P2 originates from the stress-induced reorientation of FeAl-VFe dipoles under. P2 does not appear in the Fe-Al alloys with Al less than 22% since no FeAl anti-site atoms and FeAl-VFe dipoles are produced.