The internal friction peaks correlated to the relaxation of Al atoms in Fe–Al alloys Original Research Article

Internal friction behaviors of Fe71Al29 and Fe62Al38 alloys were examined with the objective of investigation into the correlation between the internal friction and the relaxation of Al atoms in Fe–Al alloys. For the air-cooled specimens, three internal friction peaks were observed around 180 °C (P1), 340 °C (P2) and 510 °C (P3), respectively, in the first heating measurement, while only P3 peak was seen in the subsequent cooling process. For the annealed specimens only P3 peak arose in both heating and cooling measurements. The P1 and P2 peaks are dependent on the air-cooling temperature and they rise as the air-cooling temperature increases until reaching the critical temperature. They are relaxational peaks and the peak locations shift toward high temperature with increasing vibration frequency. The relaxation parameters are as follows: H1=1.03±0.08 eV and τ01=1.92×10−13±1 s for the P1 peak, and H2=1.64±0.05 eV and τ02=1.15×10−15±1 s for the P2 peak. It is suggested that the P1 peak originates from the stress-induced nn movement of Al atoms and the P2 peak from the nnn movement of Al atoms by means of thermal vacancies. The vacancies generated from rapid cooling can be annihilated by re-heating operation, leading to the P1 and P2 peaks disappeared in the subsequent cooling measurements for the air-cooled specimens. The variation in the peak height with the air-cooling temperature is in fact related to the degree of disorder or the vacancy concentration of the alloys.