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7Donetsk State Technical University, 83000, Donetsk, Artem Str. 58
DIDUS V.A., RYBALKA S.B GOLTSOV V.A.
Kinetics of the hydrogen-induced diffusive phase transformation in ND2FE14B type alloy at higher HYDROGEN pressures
At the present moment the permanent magnets produced from Nd2Fe14B type alloys reach the maximal magnetic energy (BH)max about 500 kJ/m3.
Nowadays it is possible to improve magnetic characteristics of the permanent magnets from these alloys significantly by special hydrogen treatment (HDDR-process). A characteristic feature of these alloys is the fact that upon hydrogenation they lose their thermodynamic stability and, at elevated temperatures, undergo a direct phase transformation, namely, decomposition into a hydride rare-earth component NdHx, an a-phase of Fe, and the iron boride Fe2B. Hydrogen evacuation causes the reverse phase transformation with the formation of an initial Nd2Fe14B phase but just with very fine structure.
The aim of this work is to study the kinetics of the direct phase transformation in Nd15Fe77B8 (at %) alloy by magnetic method at constant temperature and at higher hydrogen pressures then in works
As may be inferred from the experimental results an increase of hydrogen pressure at constant temperature of 750oC results in acceleration of transformation rate. So, for example, at increase of hydrogen pressure from 0.1 MPa up to 0.9 MPa the transformation accelerates in approximately 6 times.
So, a hydrogen pressure is an important kinetic factor characterizing kinetics such kinds of transformations in Nd2Fe14B type alloys.
[1] V.A.Goltsov, S.B.Rybalka, A.F.Volkov, V.V.Subbotin, Yu.G.Puti-lov. Effect of hydrogen pressure on kinetics of the hydrogen-induced diffusive phase decomposition of .R2Fe14B type alloy. Phizika i Tekhnika Vysokikh Davlenii (The Physics and Techniques of Higher Pressures), 9, No. 1 (1999) 76-80.
[2] V.A.Goltsov, S.B.Rybalka, A.F.Volkov, Yu.G.Putilov and V.A. Didus. Effect of hydrogen pressure on the kinetics of the hydrogen-induced diffusional phase transformation in an .R2Fe14B alloy. The Physics of Metals and Metallography, 89, No. 4, 2000, p. 363-366.
*E-mail: golsov@physics.dgtu.donetsk.ua
[1,2].
fir$- International Scientific Journal for Alternative Energy and Ecology Copyright©2000 by STC "TATA" July 2000, Vol. 1 166
