Abstract The effects of grain size on magnetic and mechanical properties of Dy-free Nd-Fe-B sintered magnets were studied. The grain size of the sintered magnets was varied by using different sized Dy-free Nd-Fe-B alloy feedstock powders which were ball milled to different extents. Increasing the ball milling time from 7 to 11 h caused the average particle size of the powders to decrease from 3.6 to 2.1 µm, while the average grain size of the corresponding sintered magnets decreased from 5.0 to 4.0 µm. The intrinsic coercivity Hcj and maximum energy product (BH)max of these magnets increased from 11.6 to 13.7 kOe and 41.6 to 43.6 MGOe, respectively. The finer grain magnets exhibited better thermal stability, as indicated by a smaller temperature coefficient of Hcj (−0.71%/°C). With extending ball milling time to 15 h, the magnetic properties of the magnets deteriorate, while the flexural strengths first decrease and then increase. The flexural strength improvement is attributed to the increased Oxygen content in the magnets due to finer grains. The coercivity enhancement by reduction of grain size is a promising approach to develop Dy-free Nd-Fe-B sintered magnets with better thermal stability. It is important to control the Oxygen contents in the magnets to compromise both magnetic and mechanical properties.

中文翻译：

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晶粒细化无镝钕铁硼烧结磁体的磁力学性能

摘要 研究了晶粒尺寸对无镝钕铁硼烧结磁体磁性能和力学性能的影响。通过使用球磨不同程度的不同尺寸的无镝Nd-Fe-B合金原料粉末来改变烧结磁体的晶粒尺寸。将球磨时间从 7 小时增加到 11 小时导致粉末的平均粒度从 3.6 减小到 2.1 µm，而相应的烧结磁体的平均粒度从 5.0 减小到 4.0 µm。这些磁体的内禀矫顽力 Hcj 和最大能积 (BH)max 分别从 11.6 增加到 13.7 kOe 和 41.6 到 43.6 MGOe。细晶粒磁体表现出更好的热稳定性，如较小的 Hcj 温度系数 (-0.71%/°C) 所示。将球磨时间延长至 15 小时，磁铁的磁性能变差，而抗弯强度先降低后增加。抗弯强度的提高归因于更细的晶粒导致磁体中氧含量的增加。通过减小晶粒尺寸来提高矫顽力是开发具有更好热稳定性的无镝Nd-Fe-B烧结磁体的一种很有前景的方法。重要的是控制磁体中的氧含量以损害磁性和机械性能。