Effect of microstructure changes on magnetic properties of spark plasma sintered Nd-Fe-B powders

Abstract

Abstract. In this study the SPS method was applied for low RE content (8,5% at.) and high RE content (13,5 % at.) MQ powders. The powders were sintered in a wide range of temperature, for 5 min., under pressure of 35 MPa. The low RE content grade, densified reluctantly and gained the density close to the theoretical value only for 850 o C. The coercivity decreased gradually with increasing sintering temperature. On the other hand, the densification of the higher RE content grade powder occurred much easier and the coercivity, close to the theoretical value, was achieved already at 650 o C. The coercivity of this material also decreased with increasing sintering temperature. Microstructural studies revealed that the SPS sintering process leads to partial decomposition of the Nd 2 Fe 14 B phase. The proportion of the RE-rich and iron phases increases parallel to the increasing sintering temperature. On the basis of the current results one can conclude that fabrication of high density MQ powders based magnets by the SPS method is possible, however the powders having higher RE content should be used for this purpose and the sintering temperature as low as possible, related to density, should be kept.

Net Shape 3D Printed NdFeB Permanent Magnet

“…The 3D printed magnet has a coercivity comparable to the one of the injection molded magnet, and 15% higher than for the SPS magnet. The significantly lower coercivity in the SPS magnet is explained by the grain growth during the sintering and the presence of the free iron . In terms of the remanence at room temperature, the 3D printed magnet has a slightly higher B r value than the polymer bonded magnet, and about 50% higher compared to the SPS‐sintered magnet with its reduced density (5.7 g cm −3 ) due to the unfavorable powder morphology for SPS sintering.…”

NdFeB Magnets with Well‐Pronounced Anisotropic Magnetic Properties Made by Electric Current‐Assisted Sintering

“…It is therefore described by many authors. [16,[20][21][22][23][24] Under conventional FAST/SPS conditions, isotropic properties still remain, making additional hot deformation of FAST/SPS samples necessary when aiming for anisotropic properties and high-energy products (BH) max . [25] Recently, Castle et al demonstrated that flash SPS-a specific kind of operation mode possible in conventional FAST/SPS devices-might become an attractive alternative for processing of anisotropic NdFeB magnets with optimized energy product (BH) max .…”

Magnetic and structural properties of spark plasma sintered nanocrystalline NdFeB-powders

“…By consolidation with SPS magnetically dead material can be avoided. Investigations show that magnets SPSed from Ndrich nanocrystalline alloys consolidate quite well due to the presence of Nd-rich liquid phase during sintering while Nd-Fe-B single phase and sub-stoichiometric alloys are relatively difficult to consolidate into high density magnets [16,17]. In this work we report on the influence of SPS temperature and pressure on the microstructure and magnetic properties of melt spun powders with a near-stoichiometric composition.…”