I.S. Golovin

Damping in some cellular metallic materials

The ability to absorb energy of mechanical vibrations by different cellular metallic materials with porosities from 14 to 96% (metallic foams, metallic sponges and sintered metals) is discussed. Different mechanisms of internal losses (thermoelastic and microeddy currents, magnetic domains, dislocations, microcracks) are considered in respect of low weight, peculiarities of structure and applicability for damping of mechanical vibrations.

Isothermal martensitic transformation in metamagnetic shape memory alloys

We show that in metamagnetic shape memory alloys exhibiting a magnetostructural first order phase transition the direct transition from ferromagnetic austenite to nonmagnetic martensite is isothermal. In contrast to the direct transformation, the reverse one (nonmagnetic martensite–ferromagnetic austenite) is athermal, just as are athermal both direct and reverse martensitic transformations in conventional ferromagnetic shape memory alloys. The observed asymmetry of properties of the direct and reverse phase transitions in metamagnetic alloys, together with the data on entropy change during the magnetostructural transition, evidences that the magnetostructural transition is driven by the first order lattice modification. The change in magnetic ordering is an effect accompanying the lattice modification, opposing the direct transformation and promoting the reverse one. It has been shown that relaxation effects in metamagnetic shape memory alloys are intrinsic in the direct transformation itself and do not ...

Snoek relaxation in Fe-Cr alloys and interstitial-substitutional interaction

The internal friction (IF) spectra of α-Fe, Fe-Cr ferritic alloys and Cr have been investigated in a frequency range of 0.01 to 10 Hz. A Snoek-type relaxation was found in all the investigated C doped Fe-Cr alloys, starting from pure Fe and finishing with pure Cr. The temperature location of the Snoek peak (T max ) in α-Fe was found to be 315 K (1Hz). The activation energy deduced from the T-f shift was 0.81 eV. T max in Cr was 433 K with an activation energy of 1.11 eV. The Snoek-type peaks in Fe-Cr alloys are much wider than in pure Fe or pure Cr. The temperature location of the peak versus chromium content curve exhibits a maximum in the vicinity of 35 wt% Cr (T max was 573 to 578 K, f 1.2 Hz and the activation energy was about 1.45 eV). It is important that Cr atoms in α-Fe have a more pronounced influence on the temperature location of the peak than Fe atoms have in chromium. A new model based on the atomic interactions is proposed to explain the influence of composition on Snoek peak location. The internal friction has been simulated by a Monte Carlo method, using C-C and C-substitutional atom (s) interaction energies. A model of long-range strain-induced (elastic) interaction supplemented by the chemical interaction in the two nearest coordination shells around an immobile substitutional atom was used for the C-s interaction. The interatomic interaction was supposed to affect IF by changing both the carbon atom arrangement (short-range order) and the energy of C atoms in octahedral interstices, and therefore the activation energy of IF. The peak temperatue calculated coincides well with the experimental ones if the value for the chemical interaction in the first coordination shell (H chem ) for C-Cr in Fe is -0.15 eV and for C-Fe in Cr + 0.15 eV. The difference in the influence of Cr in α-Fe and Fe in Cr is accounted for by a difference in the elastic and chemical interaction both between the carbon atoms and the substitutional atoms. The relaxation process in chromium Fe-based alloys is due to the carbon atom diffusion under stress between octahedral interstices of first and second coordination shells around the Cr atoms, and in Cr-based alloys, between second and third shells around the Fe atoms.

Effect of Substitutional Ordering on the Carbon Snoek Relaxation in Fe–Al–C Alloys

It is shown that the alloying of iron by Al (0 to 30 at%) shifts the carbon Snoek peak to a higher temperature and broadens it in the disordered state (quenched samples). Ageing of quenched samples with 19.6 at% Al shifts the peak to lower temperatures and makes it more narrow due to substitutional ordering of the DO 3 -type. The explanation of concentration dependence of internal friction and influence of ordering is done on the basis of computer simulation of energy distribution for carbon atoms in solid solution due to its interaction with Al atoms and changing of this distribution due to Al ordering. The model of the long-range strain-induced (elastic) C-Al interaction supplemented by the short-range chemical interaction is successfully used. The change of the calculated peak temperature and its width is in good agreement with experimental data. It is shown that the main factor which determines the effect of Al on the carbon Snoek peak in iron is the long-range elastic interaction.

Panel discussion on the application of HDM

In the panel discussion, various applications for damping of materials, both by passive and active damping methods, are presented by the panelists. Then, comments on high damping materials and their applications are presented by three commentators.

Mechanism of damping capacity of high-chromium steels and α-Fe and its dependence on some external factors

The influence of heat treatment on the elastic and nonelastic parameters of internal friction of high-chromium ferritic alloys and α-Fe has been examined. Mechanisms of the formation of magnetoelastic and dislocation hysteresis have been investigated. Temperature ranges and temperature and amplitude critical points connected with different damping mechanisms have been established. Heat treatment for maximum damping capacity has been suggested, and the results of damping capacity of about 50 steels were generalized.

Grain-boundary relaxation in copper before and after equal-channel angular pressing and recrystallization

Temperature-dependent internal friction and modulus of elasticity have been studied in samples of pure copper (99.95%) subjected to deformation by equal-channel angular pressing using 1, 4, and 8 passes by the route BC. The influence of deformation and subsequent recrystallization on the parameters of the internal-friction peaks caused by grain-boundary relaxation and recrystallization of severely deformed copper has been determined. Quantitative estimates of the activation parameters of grain-boundary relaxation have been obtained and the limits of its manifestation have been revealed.

Interstitial distribution in Fe-Al and Fe-Cr quenched and aged alloys: Computer simulation and internal friction study

Abstract Two types of physical approaches for simulation of the Snoek-type relaxation in low and high alloyed iron are examined to explain the experimental results obtained for Fe–Al–C and Fe–C–Cr alloys. The first approach developed by Smirnov–Tomilin is to calculate all octahedral positions available for interstitial atoms with different amount of substitute atoms in the first coordination shell and to simulate the loss maximum as a sum of all partial peaks according to the above mentioned interstice positions. The second approach takes into account the all pairwise interatomic interaction between solute atoms in a few coordination shells due to their interatomic elastic and ‘chemical’ interaction according to Khachaturyan–Blanter theory. The change of activation energy of ‘diffusion under the stress’ for interstitial atoms in that case is not a linear function of substitutional concentration in solution. Both physical models (short- and long-range interatomic interaction) for the Snoek-type relaxation in quenched ternary alloys (Fe–C–Me) are examined from the viewpoint of a distance of interatomic interaction taken into account and checked using experiments. It is shown that contrary to the second approach, the first type of calculations is reasonable for relatively low alloyed solid solution only. Decomposition (Fe–Cr) and ordering (Fe–Al) change the parameters of atomic distribution in bcc solid solution and lead to the corresponding change in the Snoek relaxation parameters. The use of an adequate physical model and structure parameters allows to explain corresponding effects and, vice versa, the internal friction spectrum allows to estimate quantitatively atom redistribution in alloyed ferrite.

Influence of carbon and nitrogen on solid solution decay

Abstract“475 °C embrittlement” of high-chromium ferritic steels with Cr content from 15 to 35 wt pct and different commercial impurities (C, N) has been investigated. The influence of preliminary treatment (600 °C to 1250 °C) and chemical composition of the alloy (Cr, C, N, Mo, Ti, Nb) on kinetics has been established. Internal friction (IF) was used to determine the contribution of interstitial atoms to the formation of Cr-modulated structure during different stages of embrit- tlement of high-chromium steels. By use of IF, static and dynamic (impact) mechanical tests with different states of stress, transmission and scanning electron microscopy of structures and fracture surfaces, and the application of diffraction methods, thermodynamic diagrams of the aging of high-chromium steels have been obtained. In the temperature range of 475 °C em- brittlement, the following sequence of processes has been established: (1) decay of solid solution supersaturated with interstitial atoms by dislocation pinning, (2) formation of substitutional- interstitial (s-i) complexes of interstitial (C, N) and substitutional (Cr) atoms, and (3) formation of zones enriched in Cr.

Effect of alloying α-Fe with aluminum, silicon, cobalt, and germanium on the snoek relaxation parameters

Parameters of Snoek relaxation in binary alloys of iron with Co, Ge, Al, and Si have been studied. The concentration of Al was varied from 1.5 to 16 at. %, and that of Si, from 3 to 10 at. %, in binary (Fe-Al, Fe-Si) and ternary (Fe-Al-Si) alloys. It has been shown that Co and Ge added to α-Fe in amounts to ∼3 at. % only wekaly affect the parameters of the Snoek peak, i.e., the height, width, and shape of the peak, as well as the activation energy for diffusion of carbon atoms. Aluminum and silicon lead to a qualitatively the same effect—a broadening of the Snoek peak on the high-temperature side, which indicates an increase in the activation energy for carbon diffusion and carbon redistribution in iron. The quantitative effects of Al and Si are different. To analyze these effects, a computer analysis of the curves of the temperature dependence of internal friction has been applied.