Nd-fe-b magnet with modified grain boundary and process for producing the same
In the conventional process, a coercitivity increase is realized by effecting selective presence of, for example, Dy metal in crystal grain boundary zones of sintered magnet. However, as this process employs a physical film forming technique using a vacuum vessel, such as sputtering, there has been a difficulty in mass productivity in the performing of vast quantities of magnet treatment. Further, from the viewpoint, for example, that an expensive high-purity Dy metal or the like must be employed as a film forming material, there has been a drawback in magnet cost.
There is provided a method of modifying the grain boundary of Nd-Fe-B magnet, characterized in that a fluoride, oxide or chloride of metal element M (M: Pr, DY, Tb or Ho) is subjected to reduction treatment so that there is effected diffusion infiltration of the metal element M from the surface of Nd-Fe-B sintered magnet having an Nd rich crystal grain boundary phase surrounding the circumferential part of Nd2Fe14B main crystal into the grain boundary phase.