The relaxation spectrum of Fe-Al alloys has been studied as a function of Al content and ordering reaction in Fe-Al. Three types of relaxation peaks are observed, with activation energies between 0.8 and 3 eV. Snoek-type relaxation is studied in Fe-(0 to 50 at. pct)Al and compared with the Snoek relaxation in pure iron (C in ␣ -Fe), chromium (C in Cr), and niobium (O in Nb). The snoek-type relaxation peak in iron (at 314 K for 1 Hz) shifts to higher temperatures with increasing Al content in iron. Significant changes in the peak parameters occur when ␣ -Fe is alloyed with Al, because of the ordering reaction in Fe-Al. Peculiarities of the carbon-atom distribution in ordered and disordered Fe-Al alloys are discussed using an atom-interaction model, in which the elastic interaction is supplemented by the chemical C-Al interaction. Two other peaks are observed only when a certain Al content is exceeded: a Zener peak for Fe-(Ͼ10 pct)Al and an X peak for Fe-(Ͼ26 pct)Al. Parameters of these peaks are discussed with respect to alloy structure. Three hypotheses are discussed for the X-peak mechanism with an activation energy about 1.7 eV. A map of relaxation peaks in the Fe-Al system is constructed.

No abstract

No 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...