TEM Study of Microstructural Changes in an Anisotropic Nd–Fe–Co–B–Zr Magnet Alloy during HDDR Process

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

“…Although the shape of lamellar cluster after the HD step was different, above microstructural change during DR step was similar even when P HD was 100 kPa. orientation between α-Fe and NdH 2 grains in the disproportionated stage was reported previously, [8][9][10][11][12][13][14] and from the present study, such an orientation relationship is found to be maintained even when the DR process is under progress. On the other hand, no relationship among recombined Nd 2 Fe 14 BH y grains as well as between Nd 2 Fe 14 BH y and α-Fe or NdH 2+x grains was observed at this stage.…”

“…1(b)) as previously reported. 10,12 Simultaneously, it is found that almost lamellar clusters had already recombined to Nd 2 Fe 14 BH y (X region in Fig. 1(b)).…”

“…This type of texture is commonly known as a hydrogen disproportionated state of Nd-Fe-B-based magnet. [8][9][10][11][12] It is a slightly difficult for the samples to avoiding absorption of the remaining hydrogen in the chamber during the cooling process of sample retrieval. Thus, the amount of hydrogen in the NdH 2+x is changed before cooling from the value at high temperature to room temperature.…”

“…7 Along with efforts to obtain the higher degree of anisotropy, investigations of the mechanism that induces such a crystallographic alignment have been intensively performed to date. [7][8][9][10][11][12][13][14][15][16] Further, from the microstructural observation as well as the analysis of orientations of crystal grains, it is now recognized that the α-Fe and NdH 2 grains formed during the HD process tend to align with some type of crystallographic orientation. [8][9][10][11][12][13][14] Currently, there are several reports that describe the details of such an orientation observed at the state where the HD step was completed; however, not enough information is available on the alignment behavior during the DR process.…”

Corroded microstructure of HDDR-NdFeB magnetic powders

“…The market of bonded NdFeB magnet is developing very fast owing to the remarkable advantages in terms of low-cost and near-net-shape manufacturing. One of the promising methods to produce NdFeB powders for bonded magnets is hydrogenation-desorption-decomposition-recombination (HDDR) process [1][2][3]. Bonded anisotropic magnet made with HDDR powders shows the magnetic energy product ðBHÞ max as high as 193 kJ/m 3 [4], which is significantly superior to the isotropic bonded magnets with 80-144 kJ/m 3 [5].…”