Consolidation of hydrogenation–disproportionation–desorption–recombination processed Nd–Fe–B magnets by spark plasma sintering

Coercivity enhancement of HDDR-processed Nd–Fe–B permanent magnet with the rapid hot-press consolidation process

“…Such a phenomenon has not been reported in previous studies using the conventional hot-press [8,[14][15][16] or the SPS apparatus [10,11]. Moreover, a high H cJ surpassing that of the initial HDDR powder by 25% has been obtained with this process.…”

“…5a and c, respectively. Aligned Nd-rich phases can be observed around the surface of fragmented HDDR particles, which is known in hot-pressed and spark plasma sintered samples [7,10]. High magnification SEM-BSE images of samples B and C are shown in Fig.…”

“…Morimoto et al [9] reported improved alignment in the final bulk magnet by hot pressing the powder at an incomplete hydrogen-desorption stage, but the coercivity of the product was somewhat lower. More recently, the spark plasma sintering (SPS) technique that enables sintering at a reduced temperature was employed [10], and improvement in the c-axis texture was demonstrated by post-sintering hot deformation [11]. However, detailed investigations of the microstructural variations and their influence on intrinsic coercivity (H cJ ) during the consolidation process were not conducted in previous investigations.…”

Rapid sintering of anisotropic, nanograined Nd–Fe–B by flash-spark plasma sintering

“…In recent years research has focussed on the use of Electric Current Assisted Sintering (ECAS) techniques such as Spark Plasma Sintering (SPS) [5][6][7][8][9]. Such techniques enable isotropic, nanocrystalline, melt-spun magnetic powders to be sintered to full density in much shorter sintering times by the application of high pressures and electric fields/currents.…”

52.7 kOe high coercivity in Sm(Co0.9Cu0.1)4.8 melt-spun ribbons

“…[4][5][6][7] It was also reported that the Cu stabilises 1:7 phase. 8,9 For high coercivity in SmCo 5 magnets, the following structure-property correlations have been understood through detailed studies: i) the presence of high anisotropic SmCo 5 single phase as the matrix, 10 ii) availability of a thin layer of nonmagnetic grain boundary phase to reduce inter-grain magnetic exchange coupling between the neighbouring grains, 11,12 iii) fine grain structure with average grain size in the range of a single domain size (750 nm) to suppress the nucleation of domain walls within the grains, 13,14 and iv) evenly distributed domain wall pinning centres (defects, precipitates and low or high anisotropic secondary phases) within the matrix where the pinning center size is in the range of domain wall thickness of SmCo 5 phase (∼3-4 nm). 15 Suresh et al 6,7 have studied Sm(Co 0.9 Cu 0.1 ) 4.8 melt-spun ribbons using 55 kOe SQUID magnetometer and reported a coercivity of 42.6 kOe in ribbons with wheel speed (WS) of 50 m/s, and the reasons for such high coercivity have been attributed to i) the formation of fine grain size, ii) the absence of unwanted phases, and iii) the presence of more fraction of 1:5 grains.…”