Inelastic effects in ordering of Fe−Al alloys

Abstract

The effects of the aluminum content in binary b.c.c, alloys of the Fe-AI system and of the processes of ordering in the substitutional solid solution on the activation energy of diffusion of carbon atoms and magnitomechanical dissipation of the energy of mechanical vibrations are studied.The method of internal friction (IF) is widely used in studying the structure of metals and alloys and various structural transformations due to its selectivity at the atomic level. In b.c.c, metals, which include the Fe -AI alloys studied, the best-known effect of relaxation inelasticity is Snoek relaxation, caused by redistribution of interstitial atoms in the field of applied stresses. The jumps of interstitial atoms caused by an alternating stress lead to the appearance of a maximum on the temperature (at f= const) and frequency (at T = const) dependences of the internal friction. The corresponding relaxation peak is described by the Debye equation for a standard solid, i.e.,where A is the degree of relaxation, co = 2xf, fis the vibration frequency, and x-~ is the frequency of the atomic jumps. Expression (I) has a maximum at o~x = 1 with a height Q-I = A/2. The jumps of the interstitial atoms under the action of the stress are elementary diffusion acts. The dependence of the relaxation time on the temperature is described by the Arrhenius equation(with the exception of superlow temperatures), where H is the activation enthalpy, k is Boltzmann's constant, and l/T 0 is the frequency of the atomic jumps at a temperature T-~ 0. The Snoek effect is traditionally studied by measuring the temperature dependence of the internal friction (TDIF). The equation for the TDIF for Snoek relaxation is obtained by substituting formula (2) into expression (1), i.e.,?.max ,( -i where Tma • and QmaIx are the temperature and height (~)max = A/2) of the maximum, the parameter ,-2 ([3) is the broadening Russian State Engineering University (K~ (-~. Tsiolkovskii Moscow Aircraft Engineering Institute), Moscow: Tula State University, Tula. Russia.with respect to the peak for a standard solid; it is introduced under the assumption that the relaxation time is normally distributed and it is determined experimentally.Expression (3) describes the Snoek peak at T = Tma x for each type of interstitial atom with allowance for the broadening function of the Debye maximum r 2 (13) due to the inhomogeneity of the solid solution. The parameter 13 determines the change in the height and shape of the IF maximum with respect to the Debye one, for which 13 = 0, the broadening parameter r 2 (13)= 1, and the parameter of the variation of the height is the function 2f2 (0, 13)= 1 [ 1]. With increase in 13, i.e., due to the normal (Gaussian) distribution of the logarithm of the relaxation time (In x), the height of the maximum diminishes and the width grows. Although in the general case the distribution of T is a result of the existence of a distribution with respect to both T o and H, the variation with respect to x 0 can be neglected in light of results of[2] that sho...

Anelasticity of Fe–Al alloys, revisited

“…15b). This effect was confirmed using torsion in [24], additionally a long-term annealing of quenched Fe- (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)%Al alloys was studied [24,34]: it practically does not influence the damping capacity of Fe-11%Al alloy, but leads to a decrease in magnetomechanical damping in alloys with higher Al concentration due to effect of ordering. Dependence of ADIF due to magneto-mechanical damping (d mmd =d AE +d dis 1 ) on measuring temperature (at torsion) in Fe-25%Al, which is not high damping composition, is shown in Fig.…”

“…The Zener type relaxation in Fe-Al was first reported in 1960 by Shyne and Sinnott [9] and then by different authors [10,11,14,15,22,24,26,30,[34][35][36][37][38][39][40][41][42][43][44]. The Snoek-type relaxation was discovered in 1962 by Fischbach [10] and later investigated in [11][12][13]16,.…”

“…Additional alloying of Fe-Al by Cr influences the Zener peak parameters. The activation energy for Zener relaxation in binary Fe- (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)Cr alloys [71] is higher than that for Fe-(15-25)Al, namely roughly 3.3-3.5 and 2.4-2.8 eV, respectively [15]. As seen from our experiments, adding chromium to Fe-Al alloys (28Al-3Cr, 15Al-15Cr) increases the activation energy of Zener relaxation [88].…”

“…Influence of carbon concentration. According to most of the published papers, the S peak in Fe-Al alloys is a Snoek-type peak [10][11][12][13][14]16,17,[20][21][22]24,25,[28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44]. It means that the origin of this peak is stress-induced diffusion of interstitial atoms (carbon atoms) in the solid solution.…”

“…Amplitude dependent internal friction (ADIF) was studied in [24,[45][46][47]88] with respect to chemical composition and magnetic structure of binary Fe-Al alloys. ADIF curves have a typical maximum which corresponds to a maximal dissipated energy due to motion of magnetic domain walls (MDW) (Fig.…”