烧结气氛对烧结NdFeB磁体显微结构的影响

对NdFeB合金的Ar保护烧结和真空烧结进行了对比研究。SEM显微观察发现,与Ar保护烧结的磁体相比,真空烧结磁体中的点状和块状富Nd相相对较小,且存在着明显的线状缺陷。蒸气压理论计算表明,真空烧结时烧结保温过程中Nd和添加元素Dy的饱和蒸气压均大大高于外压,因此Nd和Dy均存在着明显的挥发和烧损,这是造成真空烧结磁体中富Nd相较小以及存在着明显的线状晶界缺陷的主要原因。

Effects of Sintering Atmospheres on Microstructures of Sintered NdFeB Magnets

The argon atmosphere sintefing and vacuum sintering of NdFeB alloys were studied. It is found by SEM observations that compared with the magnet sintered in argon atmosphere, the magnet sintered in high vacuum has smaller punctate and lumpish Nd-rich phases, and clearly has linear defects. It is shown by the calculation with the theory of vapor pressure that in the course of vacuum sintering, the saturation vapor pressures of Nd and additional element Dy in heat preservation sintering are considerably higher than ambient pressure, therefore there obviously exist volatilizations and losses of Nd and Dy, which are the main reasons resulting in smaller fich-Nd phases and linear grain boundary defects existing in the vacuum sintered magnet.