热处理对烧结NdFeB磁体机械破碎磁粉的影响

将烧结NdFeB磁体进行机械破碎,得到粒径大小运用于制备粘结磁体的磁粉,其矫顽力很低.在700~1050℃的温度范围内进行热处理.实验结果表明:适当地选取热处理温度,可以显著地提高磁粉矫顽力,使其成为各向异性的高性能磁粉.用光学显微镜及SEM对热处理前后磁粉的形态进行了观察.未经热处理的机械破碎磁粉,颗粒边缘地区很细碎,并且有很多裂纹,中心区域则相当完整.热处理后,磁粉的边缘区域裂纹明显减少并趋于平整,同时出现明显的稀土及其氧化物的富集区.这表明,热处理过程中磁粉可能发生了氧化,或者是将吸附的氧转化成了稀土氧化物.

Influence of Heat Treatment on the Coercivity and Morphology of the Magnet Powders Prepared by Mechanical Crushing Sintered NdFeB Magnets

Heat treatment experiments were carried out to magnet powders prepared by crushing the sinteped NdFeB hard magnets, within the annealing temperature range from 700 to 1050℃. The results have shown tha the annealing treatment can effectively enhance the coercivity of the crushed powders, which is very low after the communtion, to relative high values. The microstructural changes of the magnet powders during the annealing were checked using optical and scanning electronic microscopes. It is found out that the magnet powders have many cracks in their surface layer caused by the mechanical crush, while their center parts remain free from crack. On the other side, the magnet powders after annealing treatment possess have few cracks in the surface layer. This change is considered as the result of the repairing effect of the annealing treatment to the damaged surface, which should be the reason for the enhanement of the coercivity of the magnet powders. Meanwhile, in the powders after annealing, more Nd-rich prticles can be observed evidently,some of which are determined as Nd-oxide. It indicates the ocurrence of oxidation is an other process happened during the annealing treatment,which should affect the recovery of the coercivity of the manget powders negatively.