NdFeB磁体重稀土Dy热扩渗工艺及其机制研究

Studyon process and mechanism of Dy diffusion for sintered NdFeB magnet

重稀土热扩渗技术在制备高性能、低成本烧结NdFeB磁体领域有重要的应用前景。本研究利用涂覆工艺将DyF3粉末均匀涂覆在M档商业烧结NdFeB磁体表面,获得均匀DyF3涂层,然后进行热扩渗处理。对热扩渗后磁体的性能,微观组织结构及元素分布进行分析,讨论了NdFeB磁体热扩渗工艺对其性能的影响及热扩渗机制。结果表明,本研究磁体的最佳渗Dy工艺为920℃×5h,磁体的矫顽力提高了428A/m,达到1555A/m,剩磁下降很小,磁体达到最佳的综合性能。在扩渗过程中,浓度差提供了扩渗的驱动力,在其驱动下,Dy元素从表面经由晶界向芯部扩散,距磁体表面约689μm范围内,Dy元素扩渗充分且均匀,超过该范围后Dy元素开始出现梯度分布,在本扩渗工艺Dy元素可渗透3mm厚度的磁体。

Dy diffusion process is a novel method to increase coercivity of sintered NdFeB magnets and optimize thermal performance.In this work,a facile Dy-diffusion process was carried out.DyF3 powder as Dy precusor was dispersed in a solvent,and then the NdFeB magnet was immersed into the solvent.A uniform DyF3 coating was obtained on the magent surface after dying.The magnet with Dy coating was heated to diffuse Dy under a high vacuum condition.The influence of Dy-diffusion process on the properties of magnets and mechanism of the diffusion were investigated.An optimal Dy-diffusion process was obtained when the heating treatment was conducted at 920℃for5 hours.Coercivity of the magnet treated by the optimal process has a significant increase(from 1127 A/m to1555 A/m)with a negligible decrease of remanence.Analyses of microstructure and elements distribution indicate that the diffusion was driven by the concentration difference,and the grain boundary provides a highway for the diffusion of Dy element from the surface to the inside.A magnet of 3 mm thickness could be penetrated by using this Dy diffusion process.Within the range of about 689μm from the magnet surface,the diffusion of Dy element is sufficient and uniform.Beyond this range,the Dy element begins to display in a gradient distribution.