Rare earth Nd-Fe-B, a widely used magnet composition, was synthesized in a shape of powders using gas atomization, a rapid solidification based process. The microstructure and properties were investigated in accordance with solidification rate and densification. Detailed microstructural characterization was performed by using scanning electron microscope (SEM) and the structural properties were measured by using X-ray diffraction. Iron in the form of α-Fe phase was observed in powder of about 30 μm. It was expected that fraction of Nd2Fe14B phase increased rapidly with decrease in powder size, on the other hand that of α-Fe phase was decreased. Nd-rich phase diffused from grain boundary to particle boundary after hot deformation due to capillary action. The coercivity of the alloy decreased with increase in powder size. After hot deformation, Nd2Fe14B phase tend to align to c-axis.
With the recent advancement in technology for titanium metal powder injection molding and additive manufacturing, high yield and good flowability powder production is needed. In this study, titanium powder was produced through vacuum induction melting gas atomization with a cold crucible, which can yield various alloy compositions without the need for material pretreatment. The gas behavior in the injection section was simulated according to the orifice protrusion length for effective powder production, and powder was prepared based on the simulation results. The gas distribution changes with the orifice protrusion length, which changes the location of the recirculation zone and production yield of the powder. The produced powders had a spherical morphology, and the content of impurities (N, O) changed with the injected-gas purity.
In this study, we demonstrate a facile and cost-effective way to synthesize Nd-Fe-B of various shapes such as powders, rods and fibers using electrospinning, heat-treatment and washing procedures. Initially Nd-Fe-B fibers were fabricated using electrospinning. The as-spun Nd-Fe-B fibers had diameters ranging 489 to 630 nm depending on the PVP concentration in reaction solutions. The different morphologies of the Nd2Fe14B magnetic materials were related to the difference in thickness of the as-spun fibers. The relationships between the as-spun fiber thickness, the final morphology, and magnetic properties were briefly elucidated. The intrinsic coercivity of Nd2Fe14B changed with the change in morphology from powder (3908 Oe) to fiber (4622 Oe). This work demonstrates the effect of the Nd-Fe-B magnetic properties with morphology and can be extended to the experimental design of other magnetic materials.
Liquid metal extraction (LME) process results in 100% neodymium (Nd) extraction but the highest extraction efficiency reported for Dysprosium (Dy) so far is 74%. Oxidation of Dy is the major limiting factor for incomplete Dy extraction. In order to enhance the extraction efficiency and to further investigate the limiting factors for incomplete extraction, experiments were carried out on six different particle sizes of under 200 µm, 200-300 µm, 300-700 µm, 700-1000 µm, 1000-2000 µm and over 2000 µm at 900℃ with magnesium-to-magnet scrap ratio of 15:1 for 6, 24 and 48 hours, respectively. This research identified Dy2Fe17 in addition to Dy2O3 phase to be responsible for incomplete extraction. The relationship between Dy2Fe17 and Dy2O3 phase was investigated, and the overall extraction efficiency of Dy was enhanced to 97%.
Recently, since the demand of rare earth permanent magnet for high temperature applications such as an electric motor has increased, dysprosium (Dy), a heavy rare earth element, is becoming important due to severe bias in its production. To fulfill the increasing need of Dy, recycling offers as a promising alternative. In recycling of rare earths, Hydro-metallurgical extraction method is mainly used however it has adverse environmental effects. Liquid metal extraction on the other hand, is an eco-friendly and simple method as far as the reduction of rare earth metal oxide is concerned. Therefore, liquid metal extraction was studied in this research as an alternative to the hydro-metallurgical recycling method. Magnesium (Mg) is selected as solvent metal because it doesn’t form intermetallic compounds with Fe, B and has a low melting and low boiling point. Extraction behavior of Dy in (Nd,Dy)-Fe-B magnet is observed and effect of Mg ratio on extraction of Dy is confirmed.
NdFeB anisotropic sintered permanent magnets are typically fabricated by strip casting or melt spinning. In this study, the plastic deformability of an NdFeB alloy was investigated to study the possibility of fabricating anisotropic sintered magnets using gas atomized powders. The results show that the stoichiometric composition Nd12Fe82B6 softens at high temperatures. The aspect ratio and orientation factor of Nd12Fe82B6 billets after plastic deformation were found to increase with increasing plastic deformation temperature, particularly above 800℃. This confirms that softening at high temperatures can lead to plastic deformation of Nd2Fe14B hard magnetic phases.