Crystallographic alignment in the recombination stage in d-HDDR process of Nd-Fe-B-Ga-Nb powders

Abstract

Nd-Fe-B-Ga-Nb magnetic powder was subjected to the dynamic hydrogen disproportionation desorption recombination treatment. For samples disproportionated at both 30 and 100 kPa of hydrogen pressure, the changes in the microstructure and grain orientation during recombination process were investigated. It was observed that even during the recombination process, the orientation relationship was maintained between α-Fe and NdH2+x grains formed after the disproportionation treatment at 30 kPa of hydrogen pressure, [110]α-Fe // [110]NdH2+x, (-110)α-Fe // (-220)NdH2+x. Additionally, the alignment of recombined Nd2Fe14BHy grains became clear after 30 min of DR treatment showing following orientation relationship: (001)Nd2Fe14BHy // (110)α-Fe and (110)NdH2+x. In contrast, such a relationship was not observed in the sample disproportionated at 100 kPa of hydrogen pressure. This difference in the degree of alignment was also confirmed by measuring the magnetic property of the respective samples.

Applied Magnetic Field Increases Magnetic Anisotropy in HDDR-Processed Nd-Fe-B Alloy

“…Temp. Ramp Rate [11] H 2 % in Supply Gas * [10][11][12][13][14][15][16][17][18] Dwell Temp. [19][20][21][22][23][24] Total Pressure * [25] Dwell Time [10,21,24,26,27] Gas Introduction Temp.…”

“…Ramp Rate [none] 1st Vacuum Pressure [28,29] Dwell Temp. [19,22,23,[30][31][32] 2nd Vacuum Pressure [33] Dwell Time [16,26,28,29,31,32,34,35] -…”

Relationship between Hydrogen Pressure and Temperature for Recombination Reactions in the HDDR Processing of Ce–Fe–B Alloys

“…Although various models of the induction mechanism of magnetic anisotropy during HDDR treatment have been proposed, [36][37][38] the prevailing theory is as follows. [39][40][41][42] First, it was observed that disproportionation treatment under conditions near the P H2 -T curve led to orientation relationships of [110]¡-Fe // [110]NdH 2+x and (¹110)¡-Fe // (¹220)NdH 2+x between the ¡-Fe and NdH 2+x grains. In addition, the recombined Nd 2 Fe 14 B grains were clearly aligned with orientation relationships of (001)Nd 2 Fe 14 B // (110)¡-Fe and (001)Nd 2 Fe 14 B // (110)NdH 2+x .…”

Alignment of magnetic particles in anisotropic Nd–Fe–B bonded magnets

“…[14,15] The other one is Magfine Nd-Fe-B anisotropic magnetic powder prepared using a Hydrogenation-Disproportionation-Desorption-Recombination (HDDR) route. [16,17] Each particle of the anisotropic magnetic powder of MQA-or Magfine-Nd-Fe-B contains several millions of Nd2Fe14B grains. However, the distribution of magnetic easy axes of Nd2Fe14B grains (or [001] crystallographic orientation) is not completely aligned along a single direction in each particle [15,18].…”

“…One is Magnequench anisotropic (MQA) Nd-Fe-B anisotropic magnetic powder, produced by hot-deformation (or die-upsetting) of powders derived from melt-spun Nd-Fe-B ribbons [14,15]. The other is Magfine Nd-Fe-B anisotropic magnetic powder, prepared using a hydrogenation-disproportionation-desorptionrecombination (HDDR) method [16,17]. Each particle of the anisotropic magnetic powder of MQA or Magfine Nd-Fe-B contains several million Nd 2 Fe 14 B grains.…”