• Proceedings of the Korean Magnestics Society Conference
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• 1996.05a
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• pp.42-43
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• 1996

• Journal of Magnetics
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• v.7 no.4
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• pp.138-142
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• 2002

Magnetic properties, microstructure and texture of NdFeB magnets fabricated by a modified hot working process from commercial melt-spun powders (Magnequench; MQPA, MQPB and MQPB＋) have been investigated. The hot-pressed isotropic magnet made from MQPA powder, which contains higher Nd content than that of MQPB or MQPB＋, shows higher coercivity. The magnet also shows homogenous and fine grains with higher coercivity for higher consolidation pressure. The hot-deformed MQPA magnet shows a strong anisotropy along the press direction with homogeneous platelet Nd$_2$Fe$_{14}$B grains of 50∼100nm in thickness and 200∼500nm in length. The hot-deformed MQPB＋ magnet, however, shows low remanence and low coercivity. The microstructure of the magnet consists of two areas; undeformed Nd$_2$Fe$_{14}$B grains and well-aligned but large grains with 3∼4 $\mu$m in length. Low Nd content attributes to the formation of the two different area.

• Proceedings of the Korean Magnestics Society Conference
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• 2013.05a
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• pp.50-51
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• 2013

• Journal of Powder Materials
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• v.23 no.6
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• pp.432-436
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• 2016

We investigate the microstructural and magnetic property changes of $DyH_2$, $Cu+DyH_2$, and $Al+DyH_2$ diffusion-treated NdFeB sintered magnets with the post annealing (PA) temperature. The coercivity of all the diffusion-treated magnets increases with increasing heat treatment temperature except at $910^{\circ}C$, where it decreases slightly. Moreover, at $880^{\circ}C$, the coercivity increases by 3.8 kOe in Cu and 4.7 kOe in Al-mixed $DyH_2$-coated magnets, whereas this increase is relatively low (3.0 kOe) in the magnet coated with only $DyH_2$. Both Cu and Al have an almost similar effect on the coercivity improvement, particularly over the heat treatment temperature range of $790-880^{\circ}C$. The diffusivity and diffusion depth of Dy increases in those magnets that are treated with Cu or Al-mixed $DyH_2$, mainly because of the comparatively easy diffusion path provided by Cu and Al owing to their solubility in the Nd-rich grain boundary phase. The formation of a highly anisotropic $(Nd,\;Dy)_2Fe_{14}B$ phase layer, which acts as the shell in the core-shell-type structure so as to prevent the reverse domain movement, is the cause of enhanced coercivity of diffusion-treated Nd-Fe-B magnets.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2004.11a
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• pp.33-33
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• 2004

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2003.10a
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• pp.68-69
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• 2003

• Proceedings of the Korean Magnestics Society Conference
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• 2013.12a
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• pp.90-90
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• 2013

Since discovery, NdFeB permanent magnet has replaced application of the conventional magnets rapidly because of its superior physical and mechanical properties. With increasing consumption of power combined with energy resource depletion, energy efficiency is becoming more and more inportant. According to recent reports, almost almost half of the electric power is consumed by motor, and NdFeB magnets which are the core component of the motor play a key role on improving energy efficiency of the devices. In parallel with finding alternatives energy resources, research works improving energy efficiecy have been conducted world wide. Althogh NdFeB magnets usage have been expanded to various applications, key materials such as Nd and Dy, resouces lean heavily on specific area, China. Magnetic industry revently experienced skyrocketing price fluctuatioin of rare earth at around 2008. Chineses government's regulations worsened the situation and arose a necessity to develop methods to minimize rare earth use. In this presentation, POSCO's recent research works on rare earth reduction is presented including novel powder alloying method using nitrate precursors. Also, future R&D plans for rare earth free magnets is briefly introduced as well.

• Journal of the Korean Magnetics Society
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• v.12 no.1
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• pp.34-40
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• 2002

In order to improve the microstructure of the strip cast Nd-Fe-B alloys that are frequently used for production of high energy sintered magnets, influence of various strip casting conditions on the microstructure and phase formation and distribution were investigated. Nd-Fe-B strips consisting of microstructures suitable for preparation of high energy sintered magnets could be obtained when the wheel speed was below 5 m/s. The compositional limit that can avoid the crystallization of free iron in the as-cast state was estimated to be Nd$\_$14/Fe$\_$79/B$\_$7/. Regardless of the compositional variation, <001> preferred orientation of Nd$_2$Fe$\_$14/B normal to the strip surface was always occurred below 5 m/s, which would eventually enhance the grain alignment during pressing the powder under a magnetic field. While the coercivity of the strip cast alloys increased with the increase of the wheel speed, mainly due to the refinement of Nd$_2$Fe$\_$14/B grains, it decreased with the reduction of Nd content in the alloy composition as the formation of free iron increased.

• Proceedings of the Korean Magnestics Society Conference
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• 2013.12a
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• pp.95-95
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• 2013

The NdFeB magnet can be classified into the sintered magnet and bonded magnet. The former has superior magnet characteristics but the degree of freedom in shape is highly restricted, whereas the latter has a high degree of freedom, but its magnet characteristics are inferior to the former. When a NdFeB magnet is used at the elevated temperature, part of Nd must be replaced with a high priced Dy to increase its coercive force. For these reasons, a Dy free and high performance NdFeB bonded magnet is desired strongly. The author successfully developed a Dy free NdFeB anisotropic bonded magnet based on discovery of new phenomena called as d-HDDR reaction and its mass production process such as a thermally balanced hydrogen reaction furnace, micro capsuled powder, compression molding / injection molding under magnetic field, magnetic die and so on. Applied to DC brush seat motor for automotive use, the motor has become 50% small in size and weight. The commercialization of a half sized motor for automotive use has been realized up to the market share of 30%. At present, its commercialization is extending to various types of motors such as power tool, ABS motor, wiper motor, window motor, electric bike power motor, and compressor motor. It is expected that the applications will be increasingly enlarged to EV motor, wind generator, EPS motor, washing machine, and glass cutting machine. This innovative technology has realized Dy free high performance magnet and mudt make big contribution to not only rare element strategies but also energy conservation.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.672-678
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• 1995

The magnetic separation of Nd-Fe-B powders prepared by melt-spun and HDDR processes was investigated. The experiments show that the ununiform melt-spun powders can be separated into various standards by means of magnetic separation method. The magnetic powders with higher properties were obtained by the use of suitable separating field. For example, the properties of ununiform melt-spun powders are Br=7.95 kG, iHc=9.93 kOe and (BH)max=10.2 MGOe before separating. Through separating in different magnetic fields, the powders obtained with a separating field of 780 Oe has the optimum properties of Br=7.7 kG, iHc=11.0 kOe and (BH)max=15.3 MGOe. The magnetic properties of the HDDR magnetic powder are hardly separated by the magnetic separation method.