d-HDDR Processing of Nd-Fe-B Based Alloys to Obtain Highly Anisotropic Nanocrystalline Powders

Abstract:

The HDDR (hydrogenation-disproportionation-desorption-recombination) process is an established powder metallurgy route to obtain Nd–Fe–B nanocrystalline powders for bonded magnets manufacturing. Therefore, both conventional (c-HDDR) and dynamic HDDR (d-HDDR) processes has been investigated to obtain Nd-Fe-B-based powders with different characteristics. Magnetic properties were measured by means of a hysteresisgraph and the powder obtained by d-HDDR showed strong anisotropy, allowing a B_r of 1.1 T in the bonded magnet, whereas c-HDDR powder was isotropic with a B_r of 0.6 T. Microstructural changes were characterized by X-ray diffraction (DRX) and scanning electron microscopy (SEM). X-ray patters of anisotropic powders made by d-HDDR showed high intensity reflection peaks indexed as (004), (105) and (006) planes in the aligning direction, due the texture inducement in c-axis of the main phase (Nd₂Fe₁₄B). However, SEM micrographs of c-HDDR powder showed a more homogeneous microstructure, with grain size of ~300 nm, when compared to d-HDDR powder that ranged from 300 nm to 500 nm. This difference is assumed to be the cause of lower intrinsic coercivity found in the c-HDDR powder.

• Periodical: Materials Science Forum (Volume 899)
• Pages: 563-566
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.899.563
• Online since: July 2017
• Authors: Juliano Assis Baron Engerroff*, Frederico Orlandini Keller, Leonardo Ulian Lopes, Arthur Alvarez Mascheroni, H. Takiishi, Paulo Antônio Pereira Wendhausen
• Keywords: Anisotropy, HDDR, NdFeB Magnets

References

[1] M. Liu, R. Xiao, R.W. Gao, G.B. Han: Physica B Vol. 406 (2011), p.3534.

[2] H. Mitarai, K. Noguchi, C. Mishima, H. Matsuoka, M. Yamazaki, Y.K. Aich: IEEE Transactions on Magnetics Vol. 50 (2014), p.10.

[3] O. Gutfleisch, A. Bollero, A. Handstein, D. Hinz, A. Kirchner, A. Yan, K. -H. Müller, L. Schultz: Journal of Magnetism and Magnetic Materials Vols. 242-245 (2002), p.1277.

DOI: 10.1016/s0304-8853(01)00989-1

[4] H. Sepehri-Amin, T. Ohkubo, K. Hono, K. Güth, O. Gutfleisch: Acta Materialia Vol. 85 (2015), p.42.

DOI: 10.1016/j.actamat.2014.11.003

[5] O. Gutfleisch, K. Khlopkov, A. Teresiak, K. -H. Müller, G. Drazic, C. Mishima, and Y. Honkura: IEEE Transactions on Magnetics Vol. 39 (2003), p.2926.

DOI: 10.1109/tmag.2003.815749

[6] O. Gutfleisch: J. Phys. D: Appl. Phys. 33 (2000), p. R157.