• Journal of the Korean Magnetics Society
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• v.14 no.5
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• pp.196-200
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• 2004

In order to improve dendritic formation of Nd$_2$Fe$\_$14/B phase in the strip-cast Nd-Fe-B alloys that are frequently used for production of high energy sintered magnets, effect of small substitutional additives such as Cu (0.3～1.0 at. %) and Co (0.5～1.5 at.%) on the phase formation and microstructures of the strip-cast alloys based on Nd$\_$14/Fe$\_$80/B$\_$6/ were investigated. As the amount of Cu addition increased, formation of Nd$_2$Fe$\_$14/B dendrites along the direction normal to the strip surface was suppressed with the reduction of the strip thickness mainly due to the increase of fluidity of the melt. However, both the dendrites and their <001> preferred orientation along the direction normal to the strip surface were improved with the increase of the strip thickness as the amount of Co addition increased. The dendrites became finer after small amount of Cu or Co was added. While small copper additions tended to stabilize the formation of primary Fe, small cobalt additions suppressed it. When small amount of Zr was added, however, the dendrite structures were totally collapsed with excessive grain growth of Nd$_2$Fe$\_$14/B.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2001.11a
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• pp.8-9
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• 2001

• Journal of the Korean Society for Precision Engineering
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• v.10 no.2
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• pp.146-153
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• 1993

Thd specimens were melited in high frequency induction furnace. The samples for measurements were prepared by machining cylinder of 9.5mm diameter and 15mm height. These samples were then hot-pressed according to strain rate ( .epsilon. ). These samples were decanned and cut out, and subsequently heat treated at 1000 .deg. C for 4hours. These were investigated for the change of microstructure, domain pattern, X-ray diffraction and magnetic properties. The stress distributions in the specimens during compressing process were calculated by a finite element method program(SPID). The calculated stresses were effective stress( .sigma. $_{eff}$), compressive direction stress( .sigma. $_{z}$), and shear stress( .tau. $_{rz}$ ). These stresses were compared with the experimental data.a.a.

• Proceedings of the Korean Magnestics Society Conference
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• 1993.11a
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• pp.52-53
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• 1993

• Journal of the Korean Magnetics Society
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• v.1 no.1
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• pp.17-24
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• 1991

Laves phases of $NdFe_2$, $Nd{(Fe_{0.5})}_2$, $SmCo_2$ and $Sm{(Fe_{0.5}Co_{0.5})}_2$ stoichiometry were prepared using a rapid solidification technology. Low temperature magnetic properties show ferromagnetic behaviors for the $Nd{(Fe_{0.5}Co_{0.5})}_2$, $SmCo_2$ and $Sm{(Fe_{0.5}Co_{0.5})}_2$Nd(Feo,Coo,) Laves compounds while a sort of spin reorientation has been suggested for the supposed composition of $NdFe_2$ alloy. This rapidly solidified $NdFe_2$ alloy is believed to consist of metastable rhombohedral $NdFe_7$ phase plus fine particles of Nd-rich phase. Some evidence of phase transition from the mixture of unstable $NdFe_7$ compound plus Nd-rich to $Nd_2Fe_{17}$ plus Fe-Nd-O phase was obtained after annealing the $NdFe_2$, alloy. The pseudo-binary Laves compound, $Sm{(Fe_{0.5}Co_{0.5})}_2$ exhibits a high coercivityof 4 kOe at room temperature with Curie temperature of $400^{\circ}C$ while the $Nd{(Fe_{0.5}Co_{0.5})}_2$ compound shows a magnetic moment of $2.8\;{\mu}_B/f.u.$.

• Journal of the Korean Magnetics Society
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• v.22 no.3
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• pp.85-90
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• 2012

Oxidation of the $Nd_2Fe_{14}B$ compound crystal and its effect on the coercivity of the fine $Nd_2Fe_{14}B$ crystal particles were investigated. Oxidation kinetics of the $Nd_2Fe_{14}B$ compound crystal was investigated using an excessively grown $Nd_2Fe_{14}B$ grains in the $Nd_{15}Fe_{77}B_8$ alloy ingot. Oxidation of the $Nd_2Fe_{14}B$ compound crystal occurred by dissociation of the phase into multi-phase mixture of ${\alpha}$-Fe, $Fe_3B$, and Nd oxides. Oxidation rate of the $Nd_2Fe_{14}B$ compound crystal showed no dependence on the crystallographic direction. The oxidation reaction was modeled according to simple linear relationship. Activation energy for the oxidation of $Nd_2Fe_{14}B$ compound crystal was calculated to be approximately 26.8 kJ/mol. Fine $Nd_2Fe_{14}B$ crystal particles in near single domain size was prepared by ball milling of the HDDR-treated $Nd_{15}Fe_{77}B_8$ alloy, and these particles were used for investigating the effect of oxidation on the coercvity. The near single domain size $Nd_2Fe_{14}B$ crystal particles (${\fallingdotseq}0.3\;{\mu}m$) had high coercivity over 9 kOe. However, the coercivity was radically reduced as the temperature increased in air (<2 kOe at $200^{\circ}C$). This radical coercivity reduction was attributed to the soft magnetic phases, ${\alpha}$-Fe and $Fe_3B$, which were formed on the surface of the fine particles due to the oxidation.

• Proceedings of the Korean Magnestics Society Conference
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• 1997.05a
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• pp.70-71
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• 1997

• Proceedings of the Korean Magnestics Society Conference
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• 1998.05a
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• pp.88-89
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• 1998

• Proceedings of the Korean Magnestics Society Conference
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• 1991.05a
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• pp.49-50
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• 1991

• Proceedings of the Materials Research Society of Korea Conference
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• 2002.05a
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• pp.87-87
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• 2002