CAJ | 학술논문

对高磁能积 NdFeB 永磁体的热退磁机理进行了分析。首先测量并研究永磁体开路磁通随温度的宏观变化，然后采用多功能显微镜、热分析仪及 X 射线衍射仪观察了高温金相形貌并分析了物相和表面成分变化，借助磁力显微镜观察了磁畴结构，从而分析了永磁体的热退磁机理。高温金相观察结果表明，在320℃以内，除金相形貌的颜色发生变化外，晶粒形状及尺寸均未发生明显变化；XRD 分析表明，金相形貌的颜色变化是表面氧化所致，说明磁体在320℃以内的热退磁现象与金相结构无关，即热退磁不是由金相结构变化引起的。320℃以后，XRD 及高温金相分析表明表面氧化变严重，尤其在580℃时有富 Nd 相熔融物析出，晶界模糊、大晶粒吞并小晶粒，金相结构发生明显变化。但磁畴观察结果表明，320℃内热退磁前后磁化强度方向发生偏转，方向一致性变差，是热退磁的原因所在。
대고자능적 NdFeB 영자체적열퇴자궤리진행료분석。수선측량병연구영자체개로자통수온도적굉관변화，연후채용다공능현미경、열분석의급 X 사선연사의관찰료고온금상형모병분석료물상화표면성분변화，차조자력현미경관찰료자주결구，종이분석료영자체적열퇴자궤리。고온금상관찰결과표명，재320℃이내，제금상형모적안색발생변화외，정립형상급척촌균미발생명현변화；XRD 분석표명，금상형모적안색변화시표면양화소치，설명자체재320℃이내적열퇴자현상여금상결구무관，즉열퇴자불시유금상결구변화인기적。320℃이후，XRD 급고온금상분석표명표면양화변엄중，우기재580℃시유부 Nd 상용융물석출，정계모호、대정립탄병소정립，금상결구발생명현변화。단자주관찰결과표명，320℃내열퇴자전후자화강도방향발생편전，방향일치성변차，시열퇴자적원인소재。
The demagnetization mechanism of high energy product NdFeB permanent magnet was analyzed. Firstly, changes of open-circuit magnet flux with temperature were studied. And then high-temperature metallurgical phase as well as surface composition changes were observed and analyzed using multi-functional metallographic microscope, thermal analysis instrument and X-ray diffraction, respectively. Finally we studied the phase magnetic domain structure of sintered NdFeB permanent magnet after magnetization and high-temperature treatment using magnetic force microscopy (MFM). The experimental results showed that in addition to changes in color of microstructure morphology, no obvious change occurs in grain shape and size below 320℃. XRD analysis showed that the color change is due to surface oxidation, which indicates that thermal demagnetization below 320℃ has nothing to do with the metallurgical structure. XRD and metallographic analysis also showed that surface oxidation becomes serious above 320℃, especially at 580℃ melting Nd-rich phase precipitates, the grain boundary became fuzzy and large grain annexes small one. However, magnetic domain observation showed that, magnetization direction changes after thermal demagnetization below 320℃, which is the fundamental reason for thermal demagnetization.