The interaction of dissolved atoms affects the arrangement and energies of the atoms and the asymmetry of the distortion field around a dissolved atom and thereby influences the relaxation processes in solid solutions. This review describes the strain-induced model of atom interaction along with selected examples of the model's applications for analysis of the connection between dissolved atom interaction and peculiarities of mechanical relaxations in interstitial and interstitialsubstitutional solid solutions. The strain-induced interaction is long-range, oscillating, anisotropic, and, in some solid solutions, very strong. In all the investigated cases some coordination shells show attraction. The dependence on distance is determined mainly by the type of crystal lattice; for one type of crystal lattice the dependence is determined by the type of interstitials. The energies of interstitial-interstitial (i-i), interstitial-substitutional (i-s) and substitutional-substitutional (s-s) interaction are calculated for many bcc and fcc metal solid solutions. It is found that a straininduced interaction must be supplemented by a short-range screened Coulomb repulsion in the case of i-i interaction and by a short-range 'chemical' interaction in the case of i-s interaction.The model was previously used in the analysis of: (1) the Cr concentration dependence of the carbon Snoek peak temperature in Fe-Cr-C alloys; (2) the influence of Al ordering on the carbon Snoek peak in -Fe; (3) the effect of plastic deformation on the Finkelstein-Rosin carbon peak in austenitic steels; and (4) the calculation of hydrogen internal friction peaks in Nb and Ta. It is demonstrated that the described model can explain many peculiarities of mechanical relaxations in interstitial solid solutions as observed by internal friction (mechanical spectroscopy).

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Internal friction (IF) spectra of α-Fe-FexCry-Cr ferritic alloys have been investigated with the help of forced and free decayed pendula in the frequency range 0.01 to 10 Hz. he Snoek-type relaxation has been found in all the investigated ternary alloys, iron-chromiumcarbon (Fe-Cr-C), starting with pure iron and finishing with pure chromium. The temperature of the Snoek peak (Tmax) in α-Fe is found to be 315 K (1 Hz), the activation energy deduced from the “T-f' shift is 78 kJ/mol, and the Tmax in Cr is 433 K with an activation energy 107 kj/mol. The Snoek-type peaks in Fe-Cr alloys are much wider than those in pure Fe and Cr. This is connected with the redistribution of atoms between octavoids with different numbers of Fe and Cr atoms in neighboring sites around octavoids and therefore different relaxation times. The “temperature location versus chromium content” curve passes through a maximum in the vicinity of 35 wt.%Cr, where Tmax is 573 ÷ 578 K,f = 1.2 Hz, and the activation energy is about 140 kJ/mol. The new approach, based on interaction of carbon-carbon (C-C) and carbon-substitutional C-s) atoms, is suggested for the explanation of the influence of composition on Snoek-peak location. The long-range strain-induced interactions supplemented by the “chemical” interaction in the two nearest atomic shells around a fixed substitutional atom have been used for the modeling of C-s interaction. It is suggested that the interatomic interaction affects IF by changing the carbon atom arrangement (the short-range order was simulated by the Monte Carlo method) and the energy of C atoms in octahedral interstices, that is, the activation energy of IF. The carbon atoms contribution to IF has been calculated by the Debye equation with the use of energies of C-C and C-s interaction. The Tmax shift due to the iron alloying by Cr is much stronger than that due to chromium alloying by Fe and is explained from the point of view of the above-mentioned interactions.