The effect of disproportionation conditions on the hydrogen ductilisation process for NdFeB alloys

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Hydrogen has been shown to be a very effective tool in the processing of both sintered and HDDR bonded NdFeB-type magnets. Recently, the authors have proposed a new processing technique utilising the high temperature solid‑Hydrogenation-Disproportionation (s-HD) reaction to produce a ductile mixture of α-Fe, NdH2 and Fe2B. It has been shown that, this mixture can be deformed at room temperature and recombined, under vacuum at elevated
temperatures, to form a submicron Nd2Fe14B grain structure, with a degree of anisotropy relative to the applied load. This process has been termed the “Hydrogen Ductilisation Process HyDP” [1]. However, it was shown that HyDP had several limitations which may be improved upon such as the degree of ductility, which in previous works was reduced by the presence of the minority NdFe4B4 phase [2, 3]. Cavitation was also shown to occur in the recombined microstructure, caused by redistribution of the Nd-rich phase during recombination [4], which will affect the density, remanence and coercivity of the final magnet. It has been shown in this work that variations in composition and disproportionation conditions can significantly affect the ductility of s-HD NdFeB alloys and subsequently the recombined magnetic properties of HyDP material. It has been observed that, it is possible to remove the undesirable NdFe4B4 phase through compositional changes, improving the ductile behaviour. Furthermore, the disproportionation conditions used in the previous studies [1, 2] may be modified to significantly reduce the time required for complete disproportionation whilst also increasing the fine lamella structure required for high coercivity.

[1] O. Brooks, A. Walton, W. Zhou and I. Harris, “The Hydrogen Ductilisation Process (HyDP) for shaping NdFeB magnets,” Journal of Alloys and Compounds, vol. 703, p. 538–547, 2017.
[2] O. Brooks, A. Walton, W. Zhou, D. Brown and I. Harris, “Complete ductility in NdFeB-type alloys using the Hydrogen Ductilisation Process (HyDP),” Acta Materialia, vol. 155, pp. 268-278, 2018.
[3] V. Yartys, O. Gutfleisch and I. Harris, “Hydrogen-induced phase and magnetic
transformations in Nd1.1Fe4B4,” Journal of Magnetism and Magnetic Materials, vol. 157, no.0304-8853, pp. 119-120, 1996.
[4] A. Williams, O. Gutfleisch and I. Harris, “S-HDDR induced cavitation in NdFeB,” Journal of Alloys and Compounds, vol. 232, pp. 22-26, 1996.

Bibliographic note

Abstract presented at conference.


Original languageEnglish
Title of host publicationJEMS2019 Abstract Book
Publication statusPublished - 28 Aug 2019
EventThe Joint European Magnetic Symposia (JEMS) - Uppsala Konsert & Kongress, Uppsala, Sweden
Duration: 26 Aug 201931 Aug 2019


ConferenceThe Joint European Magnetic Symposia (JEMS)
Abbreviated titleJEMS 2019
Internet address