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펄스자장을 이용한 고이방화 Nd - Fe - B 자석의 종축자장성형방법
김동환(Donghwan Kim),강병길(Byungkill Kang),장동열(Dongyoul Jang),김승호(Andrew S. Kim),김상면(Sangmyun Kim),장태석(T. S. Jang) 한국자기학회 2003 韓國磁氣學會誌 Vol.13 No.4
A new axial pressing method using pulse magnetizing field was studied to improve the remanence of Nd-Fe-B sintered magnets. In order to make near-net shape green compacts of butterfly, disk, or coin magnets, conventional axial-type pressing has been normally used. However, compared to the transverse-type pressing, it is not possible to obtain higher remanence by this method because the magnetic alignment of powder begins to deteriorate when the density of green compacts increases over a critical value. On the other hand, we found that an axial pressing under pulse magnetizing field was very effective to increase the degree of magnetic alignment of powder, yielding remanences even higher than those obtained by the transverse pressing. In this study, it was revealed that appropriate tapping density and how to apply pulse magnetic field were important to improve the grain alignment and thus remanence of Nd-Fe-B sintered magnet.
Strip - cast 조건이 Nd - Fe - B 합금의 미세조직 형성에 미치는 영향
이대훈(D.H. Lee),장태석(T.S. Jang),김동환(D.H. Kim),김승호(Andrew S. Kim) 한국자기학회 2002 韓國磁氣學會誌 Vol.12 No.1
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 ㎧. The compositional limit that can avoid the crystallization of free iron in the as-cast state was estimated to be Nd₁₄Fe_(79)B_7. Regardless of the compositional variation, <001> preferred orientation of Nd₂Fe₁₄B normal to the strip surface was always occurred below 5 ㎧, 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 Nd₂Fe₁₄B grains, it decreased with the reduction of Nd content in the alloy composition as the formation of free iron increased.
소량의 첨가원소가 Strip - Cast Nd - Fe - B 합금의 미세 조직 형성에 미치는 영향
이대훈(D. H. Lee),장태석(T. S. Jang),김동환(D. H. Kim),김승호(Andrew S. Kim) 한국자기학회 2004 韓國磁氣學會誌 Vol.14 No.5
In order to improve dendritic formation of Nd₂Fe₁₄B 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 Nd₁₄Fe_(80)B_6 were investigated. As the amount of Cu addition increased, formation of Nd₂Fe₁₄B 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 Nd₂Fe₁₄B.