The HDDR behaviour of crystalline and amorphous rapidly quenched NdFeB

• Published in: Journal of alloys and compounds 1995-04, Vol.221 (1), p.180-186
• Main Authors: Book, D., Harris, I.R., Manaf, A., Ahmad, I., Davies, H.A.
• Format: Article
• Language: English
• Subjects: Amorphous; Applied sciences; Condensed matter: structure, mechanical and thermal properties; Disproportionation; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; HDDR; Hydrogen; Metals. Metallurgy; Nd 2Fe 14B; Physics; Solubility, segregation, and mixing; phase separation
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/0925-8388(94)01432-9

The disproportionation and recombination reactions in which Nd 2Fe 14B decomposes into αFe, Nd hydride and Fe 2B in hydrogen and then reforms under vacuum, have been investigated in melt-spun ribbon with the compositions Nd 13.1Fe 82.4B 4.5 and Nd 18Fe 76B 6. TPA and DTA investigations have shown that hydrogen absorption and desorption are more rapid in the amorphous Nd 13.1Fe 82.4B 4.5 ribbon cast at 30 m s −1 than in the fully crystalline ribbon of this composition, spun at 10 m s −1. Disproportionation was found to occur in two stages in 30 m s −1 ribbon, the first stage in the range 400–500 °C associated with the amorphous phase, and the second stage in the range 500–700 °C due to the presence of crystalline Nd 2Fe 14B phase. By selecting ribbons with the smallest thicknesses, it was possible to investigate totally amorphous material on a Faraday balance, and these studies showed that, in this material, the disproportionation reaction was very rapid, and finished at 500 °C. This is in agreement with the observations on the two-phase material. In addition, DTA desorption measurements showed that recombination was more rapid and took place at a lower temperature in 30 m s −1 ribbon disproportionated at 500 °C compared with that disproportionated at 800 °C, suggesting a coarsening of the disproportionated microstructure at the higher temperature.