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Desorption–recombination and microstructure change of a disproportionated nanostructured NdFeB alloy

Published online by Cambridge University Press:  31 January 2011

Hu Lianxi ,
Li Yuping ,
Yuan Yuan  and
Shi Gang
Hu Lianxi*
Affiliation:
School of Material Science and Engineering, Harbin Institute of Technology, Harbin 150001, People’s Republic of China
Li Yuping
Affiliation:
School of Material Science and Engineering, Harbin Institute of Technology, Harbin 150001, People’s Republic of China
Yuan Yuan
Affiliation:
School of Material Science and Engineering, Harbin Institute of Technology, Harbin 150001, People’s Republic of China
Shi Gang
Affiliation:
School of Material Science and Engineering, Harbin Institute of Technology, Harbin 150001, People’s Republic of China
*
a) Address all correspondence to this author. e-mail: [email protected]
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Abstract

The desorption–recombination behavior of a mechanically disproportionated, nanostructured Nd12Fe82B6 alloy was investigated by differential scanning calorimetry and thermogravimetric analysis. The microstructure change due to desorption–recombination treatments at various temperatures was characterized by x-ray diffraction, Mössbauer study, and transmission electron microscopy observation. The results show that the hydrogen desorption of the as-disproportionated alloy occurs in two stages: (i) the partial dehydriding of the Nd hydride from Nd2H5 to NdH2, as well as the desorption of the hydrogen absorbed/adsorbed at sites of crystal defects but not in the form of Nd hydride, at temperatures between 180 and 460 °C; and (ii) the complete dehydriding of the Nd hydride from NdH2 to Nd at temperatures between 630 and 780 °C. The recombination of α-Fe with Fe2B and Nd to form Nd2Fe14B occurs following the dehydriding of NdH2 to Nd, and it acts as the controlling step for the whole desorption–recombination process. The kinetics of both the desorption–recombination reaction and the growth of the newly formed Nd2Fe14B grains accelerate with increasing temperature. For a fixed annealing time of 30 min, the optimal processing temperature seems to be 760 °C, which gives rise to a fully recombined Nd2Fe14B–α-Fe nanocomposite microstructure with Nd2Fe14B and α-Fe phases of 25–30 nm in average size.

Keywords

MicrostructureNanostructureNd
Type
Articles
Information
Journal of Materials Research , Volume 23 , Issue 2 , February 2008 , pp. 427 - 434
Copyright
Copyright © Materials Research Society 2007

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References

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