N.Ya. Rokhmanov’s research while affiliated with Simon Kuznets Kharkiv National University of Economics and other places

Fe-Al alloys containing 25 and 31.5 at. % Al have been studied by internal friction, X-ray diffraction and dilatometric analyses. These techniques show for the first time that two internal friction peaks appear during the change in long range order type which occurs during the precipitation at 300degreesC of the metastable phase B2(FeAl). These peaks correspond to the formation of two phases : the equilibrium phase Fe3Al and a new intermediate tetragonal phase theta.

Fe-Al alloys containing 25 and 31.5 at. % Al have been studied by internal friction, X-ray diffraction and dilatometric analyses. These techniques show for the first time that two internal friction peaks appear during the change in long range order type which occurs during the precipitation at 300°C of the metastable phase B2(FeAl). These peaks correspond to the formation of two phases: the equilibrium phase Fe$_3$Al and a new intermediate tetragonal phase $\theta$.

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 α-Fe), chromium (C in Cr), and nibium (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 α-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-(>10 pct)Al and an X peak for Fe-(>26 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.

The use of various experimental techniques as differential dilatometry, differential scanning calorimetry, optical and transmission electron microscopy, internal friction, electrical resistance and microhardness measurements, shows their importance and their complementarity in the study of the ageing process in Al–12 wt.% Mg alloy. Indeed, their sensitivity to various precipitation stages is different and can give more information to describe the evolution of the structure, the nature and the morphology of the precipitated phases particles and the transition between them, which is not, yet, well established. The obtained dilatometric curves show numerous effects which have been discussed. During ageing of a supersaturated solid solution Al–12 wt.% Mg it seems that β′ and β phases do not grow at the expense of GP zones (and/or β″) and β′, respectively.

The method of intemal friction has important perspectives in the study of microprocesses slticlt occur during structural transformation in materials. In the present work we show the large possibilities of this type of study in the investigation of anomalous and non linear eltects due to trarrsistorl'processes. A new method of study of the anomalous effects of intemal friction entirely rr'alised in laboratory, is proposed and its possibilities are illustrated on Fe-1.7 wt% C and Fe-wt% Ni alloy (lnvar). On the latter a new peak of intemal friction is observed for the first time.

A method for studying microplasticity of metallic materials based on in situ measurement of internal friction at low sonic frequencies (f similar to 100 Hz) is described. The method uses a relaxometer consisting of a torsional pendulum and a reversible twisting device with a Pi-shaped grip, which allows one to induce strain in relatively thick specimens of diameter to 3 - 4 mm and to measure the residual strain gamma(r) after a cycle of alternating torsion and half-cycles of repeated (of the same sign) torsion.