Anelasticity correlated to vacancies in B2 Fe–Al alloys

Abstract

Internal friction behaviors of B2 Fe -Al alloys were examined to understand the correlation between the anelasticity and thermal vacancies. Three internal friction peaks were found in the rapidly cooled specimens at around 210 °C (P1), 410 °C (P2) and 520 °C (P3), respectively, while in the slowly cooled specimens, the P1 peak was significantly decreased and the P2 peak was decomposed into two peaks (P2 L and P2 H ). All the internal friction peaks showed relaxational nature and they shifted toward high temperature with increasing frequency. It is suggested that the P1 peak originates from the reorientation of the divacancies composed of Fe vacancies and the nearest-neighboring Al vacancies, the P2 L peak from the dissociation and diffusion of the interstitial carbon atoms from the carbon-vacancy complexes and the P2 H peak from the reorientation of the triple defects.

The internal friction peaks correlated to the relaxation of atomic defects in Fe47Al53 alloy

“…In our previous work [4], a peak similar to the present P1 peak was observed in the Fe-rich B2 FeeAl alloys and it was demonstrated to be related to the reorientation of the triple defects composed of two neighboring vacancies and one Fe Al . For the present Al-rich B2 FeeAl alloys, however, the predominant defects are Al Fe and vacancies that should be responsible for the appearance of the P1 peak [20,21].…”

“…The other peaks in Figs. 11 and 12 are related to other mechanisms and are not discussed in the current study [4].…”

“…The other peaks in Fig. 10 have been proved to be attributed to other mechanisms and will not be discussed in the present study [4]. Since the increase of Al content can be accompanied with the increase of the V Fe [20,21,26], it is reasonable that the influence of Al on the P1 peak actually reflects that of the V Fe .…”

“…It has been found that the Al content significantly influences the IF behavior of FeeAl alloys. With increasing Al content, the Snoek peak shifts to high temperatures and becomes broad as a result of CeAl long-range 'elastic' interaction [2,3], while the IF peak that is correlated to the vacancies and C atoms is elevated due to the increase in the vacancy concentration [3,4]. In the alloys with relatively high Al contents such as more than 25 at%, ordering significantly suppresses the Zener relaxation [2,5], and the Zener peak is impossible appearing in completely ordered structures [6].…”

High-temperature relaxation analysis in a fine-grain B2 FeAl intermetallic

“…On the other hand, we expect diffusional processes to play an important role due to high equilibrium vacancy concentration in the B2 phase region [27,28]. In fact, the presence of Zener relaxation, which is caused by a stress-induced reorientation of solute atom pairs through the exchange of a vacancy, has been found to occur at 780 K (at 1 Hz) with an activation enthalpy about Q z ¼ 2.4 eV [14,29]. The value measured by positron lifetime spectroscopy [30][31][32] gives a slightly higher activation energy for selfdiffusion Q SD ¼ 2.7 eV.…”