【摘要】 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。更多还原

【Abstract】 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.更多还原