Materials Science and Engineering A 442 (2006) 86–91 Zener relaxation in ordered and disordered Fe–(22–28%)Al alloys I.S. Golovin a,∗,1 , A. Rivi` ere b a Institute for Materials, Technical University of Braunschweig, Langer Kamp 8, Braunschweig D-38106, Germany b LMPM ENSMA, UMR CNRS 6617, F-86961 Futuroscope Chasseneuil Cedex, France Received 26 July 2005; received in revised form 5 December 2005; accepted 23 April 2006 Abstract The Zener relaxation in three Fe–Al alloys with 22, 26 and 28 at.% Al has been studied by isothermal measurements of elastic-energy-dissipation as a function of vibrating frequency in the range from 10 -4 to 10 2 Hz. The activation energy of the Zener relaxation has been determined as follows (in kJ/mol): 238 in Fe–22Al of the disordered bcc (A2) structure, 270 in Fe–22Al of the D0 3 + A2, two phase structure, 235 in Fe–26Al of the B2 ordered structure, 286 in Fe–26Al of the D0 3 ordered structure, and 276 in Fe–28Al–3Cr at temperature close to the D0 3 ↔ B2 transition. © 2006 Elsevier B.V. All rights reserved. Keywords: Ordered alloys; Internal friction; Zener relaxation 1. Introduction Anelastic effects in Fe–Al alloys can be classified as fol- lows [1]: the dislocation-related D peaks with the mean value of activation energy H D ≈ 48 kJ/mol; the carbon Snoek-type relax- ation with the H S increasing from 81 kJ/mol in pure iron to about 125 kJ/mol in high Al containing alloys, the X relaxation with the H X about 155–160 kJ/mol caused by complexes of vacancies and carbon atoms, the Zener relaxation (H Z = 210–280 kJ/mol) and the grain boundary (GB) relaxation with higher acti- vation energy. The Zener relaxation is the subject of this paper. The Zener relaxation [2] in Fe–Al alloys was first reported by Shyne and Sinnott [3] and then by other authors [4–6]. In all these papers the Zener peak was measured in non-equilibrium conditions, i.e. during heating or cooling. We measured the internal friction of Fe–Al alloys as a function of temperature, using an inverted torsion pendulum (f ≈ 1–3 Hz) and a vibrat- ing reed technique (f ≈ 150–600 Hz). These results are similar to earlier publications reviewed by Golovin et al. [1]: the Zener peak is observed in the D0 3 ordered state at sub-hertz frequen- cies and in the B2 ordered state at kHz frequencies. Thus, by varying the frequency, the Zener peak in Fe–Al can be shifted ∗ Corresponding author. Tel.: +49 531 3913066; fax: +49 531 391 3058. E-mail address: i.golovin@tu-bs.de (I.S. Golovin). 1 On leave from Physics of Metals and Materials Science Department of Tula State University, Lenin ave. 90, Tula 300600, Russia. from one phase to another, which hinders determination of activation parameters of the relaxation for a particular ordered structure. In this work we carried out isothermal mechanical spec- troscopy experiments on Fe–Al alloys: internal friction was measured as a function of frequency at a constant temperature, in a chosen range of temperatures [7]. The Zener peak, in par- ticular its activation parameters, has been measured for various compositions and temperatures, where the alloys have different atomic structures. 2. Experimental procedure In addition to standard methods of structural characteriza- tion such as calorimetry (DSC), microscopy (TEM) and X-ray (XRD) diffraction, the following mechanical spectroscopy tech- niques were employed: (1) Two ordinary free-decay apparatuses operating at 1–3 and 200–600 Hz, which measure internal friction Q -1 as a func- tion of temperature T, were used. Peak positions (T, f) are shown in the figures in this paper (indicated by stars). (2) A forced torsion pendulum was also used. In forced vibra- tion, Q -1 is equal to tan ϕ, where ϕ is the phase lag between the applied cyclic stress and the resulting strain. The frequencies were varied between 10 -4 and 300 Hz, and measurements were made at ten frequencies per decade. The dimensions of the sample were 64 mm in length and 0921-5093/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2006.04.131