渗Dy处理对烧结NdFeB磁体结构与磁性能的影响

在工业生产线上制备35H、40H烧结钕铁硼磁体,应用DyF_3粉末作为镝源,进行渗镝处理试验。应用比较高的渗镝处理温度、比较长的渗镝处理时间有利于提高渗镝处理磁体的内禀矫顽力;在一定的渗镝处理温度和时间条件下,随着磁体厚度减小,渗镝处理磁体的内禀矫顽力明显提高。在1218 K保持2 h而进行渗镝处理,3.0 mm厚度40H磁体的内禀矫顽力上升幅度达到406.7 kA/m,其剩磁下降0.0187 T;而3.0 mm厚度35H磁体的内禀矫顽力上升363.8 kA/m,其剩磁下降幅度为0.0198 T。SEM与EDAX分析结果表明,Dy元素扩散进入富稀土晶界相中,并存在于主相晶粒表面区域,从而使渗镝处理磁体内禀矫顽力大幅度上升,同时其剩磁仅略微下降。

Effects of grain boundary Dy-diffusion on the microstructure and magnetic properties of sintered Nd-Fe-B magnets

Grain boundary diffusion process experiments with DyF3 powders were conducted on mass-produced 35H and 40H sintered Nd-Fe-B magnets. According to the experimental results, higher diffusion temperature and longer diffusion time led to a larger rise in intrinsic coercivity of grain boundary diffusion processed magnets; for given diffusion conditions, grain boundary diffusion processed magnets with smaller thickness exhibite larger rise in intrinsic coersivity. A grain boundary diffusion process at 1218 K for 2 h produces a 406.7 kA/m intrinsic coercivity increase and a 0.0187 T remanence decrease for 20 mm× 15 mm× 3.0 mm 40H magnet, and a 363.8 kA/m intrinsic coercivity increase and a 0.0198 T remanence decrease for 20 mm× 15 mm× 3.0 mm 35H magnet, respectively. According to the SEM observation and EDAX analysis, Dy diffuses into the intergranular Nd-rich phase and also exists in the surfacial region of matrix phase grains, which is believed to be the basic reason for the substantial rise in intrinsic coercivity and a certain degree of descent in remanence of grain boundary diffusion processed magnets.