Microstructure refinement of Nd-Fe-B permanent magnets prepared via spark-plasma sintering

Abstract

Sintered Nd-Fe-B-type permanent magnets are normally manufactured using a conventional powder-metallurgy approach. The limitations of such high-temperature, pressureless sintering methods include restricted control over the microstructure due to grain growth and constraints on the magnet’s geometry. The modern spark-plasma sintering (SPS) technique employs Joule heating and external pressure to offer lower consolidation temperatures and faster heating cycles compared to conventional approaches. As a result, the SPS has the potential for the rapid, low-temperature, net-shape manufacture of magnets. However, the nonequilibrium conditions associated with the SPS can lead to poor grain-boundary wetting and the formation of the soft-magnetic α-iron phase in samples prepared from anisotropic, microcrystalline Nd-Fe-B powders produced by standard procedures, i.e., strip casting, hydrogen decrepitation, and jet-milling. This study revealed that the absence of the Nd-rich grain-boundary film is related to the presence of hydrogen. Degassing the Nd-Fe-B powder before applying the SPS improved the distribution of the grain-boundary phase. Moreover, reducing the electrical currents in the sample during the SPS prevented the decomposition of the RE2Fe14B matrix, ensuring a favorable phase composition. Compared to magnets conventionally sintered at 1070 °C, the mean grain diameter of the SPS samples prepared at ≈880 °C was reduced by ≈33%. This reduction decreased the temperature coefficient of coercivity from -0.65 to -0.58%/°C. The coercivity increase measured for the SPS samples amounted to more than 15%, which was attributed to the combined effect of smaller grain size and reduced texture.

Keywords

sintranje;spark-plasma sintering;microstructure refinement;

Data

Language:	English
Year of publishing:	2024
Typology:	1.01 - Original Scientific Article
Organization:	IJS - Jožef Stefan Institute
Publisher:	IEEE
UDC:	537
COBISS:	199982339
ISSN:	1941-0069
Views:	161
Downloads:	84
Average score:	0 (0 votes)
Metadata:

Other data

Secondary language:	Slovenian
Secondary keywords:	Magneti;
Source comment:	Nasl. z nasl. zaslona; Opis vira z dne 27. 6. 2024;
Pages:	str. [1-6]
Volume:	ǂVol. ǂ60
Issue:	ǂiss. ǂ8, article no. 2100406
Chronology:	Aug. 2024
DOI:	10.1109/TMAG.2024.3417611
ID:	26125419