Origin of magnetic anisotropy formation in the HDDR-process of Nd2Fe14B-based alloys (original) (raw)
Related papers
Acta Materialia, 1999
ÐTo understand the disproportionation and anisotropy-inducing mechanism of the hydrogen-ation±disproportionation±desorption±recombination process of Nd 2 Fe 14 B-based anisotropic magnets, the disproportionated structure of Nd 13.0 Fe 67.9 Co 11.0 B 7.0 Ga 1.0 Zr 0.1 alloys has been investigated via transmission electron microscopy. An intermediate hydrogenation phase of the tetragonal Fe 3 B (t-Fe 3 B) has been revealed to appear in the early stage of disproportionation. The t-Fe 3 B possesses lattice coherency and an associated``one-to-one'' orientation relationship with the parent Nd 2 Fe 14 B phase. Within the t-Fe 3 B grain, ®ne Nd 2 Fe 14 B particles exist along with NdH 2 particles. The diameter of the Nd 2 Fe 14 B particles is around 50 nm, and they have close orientation to that of original Nd 2 Fe 14 B. An anisotropy-mediating disproportionation scheme with the intermediate hydrogenation phase is proposed.
Journal of Magnetism and Magnetic Materials, 1996
Lorentz transmission electron microscopy and optical Kerr microscopy studies of the hydrogenation, decomposition, desorption and recombination (HDDR)-processed anisotropic Nd2FeHB-based magnets show that a magnetic domain structure develops in which a unit domain includes a number of submicron Nd2Fel4 B grains coupled by the intergrain-exchange interaction. Grain boundaries and particles of an intergranular phase have been observed to pin the domain boundary walls, and their magnetic characteristics and distribution may determine the size of magnetic domains forming in a thermally demagnetized state. Measurements of differential susceptibilities indicate that the motions of the domain walls become sluggish after magnetization and dc-field demagnetization, compared to that in a thermally demagnetized state.
HDDR process of NdFeB with an excess of intergranular Nd-rich phase under magnetic field
Journal of Alloys and Compounds, 1997
Hig~ coercive isotropic Nd=Fe~B powders can be obtained using the hydrogenation-disproportionation-desorption-recombination (HDDR) process. In order to produce ani.mtropic coercive powders, a static magnetic field of 7 T has been ~pplied during the recombination stage, using an Nd-Fe~B alloy, with an excess of intergranular Nd/Cu eutectic, in parallel, the behaviour of the Nd/Cu eutectic h~s been studied by in-situ neutron diffraction experiments: under hydrogen, the Nd/Cu eutecti¢ i~ ~lid in tall temperature ranges, but under vacuum, hydrogen desorbs and the Nd/Cu becomes liquid. To induce a rolalion of the magnetic Nd~ Fet~ B cry~t~dlite.~, it i.~ necessary to teach a pronounced desorption of hydrogen. Hence, we have ~¢n ~b!¢ to produce ~lni~tropi¢ Nd~Fe~B material unde~ a magnetic field by increasing the holding time during the re¢ombin~lion ~t~e of the HDDR proce~. ~ 1~7 El~vier Science S.A.
Relationships between the coercivity of hydrogenation disproportionation desorption recombination (HDDR) Nd 12.5 Fe 81.5−x Co 6 B x bonded magnets and boron content were investigated. Nd 2 Fe 17 phase with planar magnetic anisotropy is present in the microstructure when x= 4at%-5.88at%, which does not reduce the coercivity of the bonded magnets. High-resolution transmission electron microscopy (TEM) images show that Nd 2 Fe 17 phase exists in the form of nanocrystals in the Nd 2 Fe 14 B matrix. There is an exchange-coupling interaction between the two phases so that the coercivity of HDDR Nd 12.5 Fe 81.5−x Co 6 B x bonded magnets is hardly reduced with a decrease in boron content.
Nd2Fe17 nanograins effect on the coercivity of HDDR NdFeB magnets with low boron content
International Journal of Minerals, Metallurgy, and Materials, 2012
Relationships between the coercivity of hydrogenation disproportionation desorption recombination (HDDR) Nd 12.5 Fe 81.5−x Co 6 B x bonded magnets and boron content were investigated. Nd 2 Fe 17 phase with planar magnetic anisotropy is present in the microstructure when x= 4at%-5.88at%, which does not reduce the coercivity of the bonded magnets. High-resolution transmission electron microscopy (TEM) images show that Nd 2 Fe 17 phase exists in the form of nanocrystals in the Nd 2 Fe 14 B matrix. There is an exchange-coupling interaction between the two phases so that the coercivity of HDDR Nd 12.5 Fe 81.5−x Co 6 B x bonded magnets is hardly reduced with a decrease in boron content.
Journal of the Korean Physical Society, 2017
The anisotropy of the Nd2Fe14B powder is originated during the creation of a fine Fe2B lamellar structure in the disproportionation step. The aspect ratio (A/R) of Fe2B structure increased from 3.37 ± 1.5 to 6.69 ± 3.2 during phase decomposition for 0 ∼ 60 min at 820 • C (PH2 = 10 kPa). The Fe2B having high A/R ratio recombined Nd2Fe14B, which is close to the single domain, and the magnetic properties are also improved with increasing A/R ratio.
Journal of The Less Common Metals, 1990
The microstructur~s of magnets fabricated by the hydrogen decrepitation process and a conventional route have been compared using transmission electron microscopy. The results reveal that magnets produced by the conventional technique contain particles of neodymium-rich and boron-rich phases in the hard magnetic Nd,Fe,,B grains, whilst this matrix phase is found to be almost free of neodymium-rich particles in the magnets produced by the hydrogen decrepitation route, but the boron-rich particles still exist within the matrix phase. In addition, in both routes the microstructure showed that the Nd,Fe,,B grains have a clean and faultless structure. Magnetic domain walls have been observed within the Nd*Fe,,B phase using Lorentz electron microscopy with no special stage. The result shows that all the domain walls end, and are impeded, at the neodymium-rich regions around the grain boundaries, confirming that HCi in the sintered Nd-Fe-B magnets is nucleation-controlled rather than pinning-controlled inside the matrix phase.