Kinetics of hydrogen-induced direct phase transformation in Y2Fe17 hard magnetic alloy

Abstract

Донецкий национальный технический университет, ул. Артема 58, 83000 ДонецкThe kinetics of hydrogen-induced direct phase transformation, i.e. decomposition process of Y 2 Fe 17 initial alloy at interaction with hydrogen on YH 2 hydride phase and a-Fe phase of iron, in Y 2 Fe 17 hard magnetic alloy has been studied. It has been established that, as the temperature increase from 610 to 750˚С, a direct phase transformation significantly accelerates. The activation energy of phase transformation process has been determined from kinetic data (163÷242 kJ/mol) that it is correspond to the values of activation energy of the iron atoms diffusion in R-T type alloys. It has been shown that the kinetics of hydrogen-induced direct phase transformation in Y 2 Fe 17 hard magnetic alloy is controlled by the Fe atoms diffusion to growing new a-Fe phase centers.

Kinetics of hydrogen-induced reverse phase transformation in Y2Fe17 hard magnetic alloy

“…Because of this the obtained activation energy for reverse phase transformation is similar with activation energy for hydrogen-induced direct phase transformation in the same Y 2 Fe 17 alloy (163÷242 kJ / mol [12]). …”

“…Earlier for Y 2 Fe 17 alloy above-mentioned kinetic peculiarities have been established for direct transformation [12] and therefore, the main aim of present paper was to study the features of kinetics of the hydrogen-induced reverse phase transformation (see Eq. (2) …”

Kinetic model for hydrogen-induced direct phase transformations in R2Fe17 (R - Sm, Y) type alloys

“…The slopes of the straight lines give us the values of the effective activation energies for hydrogen induced direct phase transformations. The obtained values of an activation energy determined for some degrees of transformation varying from 109 up to 230 kJ/mol for Sm 2 Fe 17 alloy [9] and from 162 up to 242 kJ/mol for Y 2 Fe 17 alloy [11]. Obtained above values of effective activation energy in low temperature region (330-750°C) have good agreement with an activation energy of data for diffusion of Fe atoms in Rare-Earth metals -Q=250 kJ/mol [17] and self-diffusion of Fe atoms in α-Fe phase of iron ~250.6 kJ/mol [18].…”

“…The isothermal kinetic diagrams of the hydrogen induced direct phase transformations in Sm 2 Fe 17 and Y 2 Fe 17 alloys were obtained experimentally earlier [9][10][11]. However, to the present moment some kinetic equation describing isothermal kinetic diagram above-mentioned phase transformations doesn't exist.…”

“…Earlier on a base of detailed kinetic investigations, SEM and X-ray diffraction studies during direct phase transformation (see Eq. (1)) in Nd 2 Fe 14 B, Sm 2 Fe 17 and Y 2 Fe 17 type alloys it was established that transformations of this type maybe classified as diffusive phase transformation in solid state and that the direct transformation process proceeds by the nucleation and growth mechanism [9][10][11][12][13][14].…”