Preparation of Highly Textured Hydrogenation–Disproportionation–Desorption–Recombination Powders for Nd–Fe–B Sintered Magnets

Abstract

Developing Dy-free Nd-Fe-B sintered magnets with high coercive force is a current research hot topic of rare earth permanent materials. Refining the Nd 2 Fe 14 B grains is an effective way to enhance the coercivity[1]. A coercivity as high as 19 kOe has been reported in Dy-free sintered Nd-Fe-B magnets when the grain size is reduced to about 1 μm[2]. It has been shown that the coercivity of sintered Nd-Fe-B magnets is inversely proportional to the logarithm of the square of grain size[1]. Thus, it is possible that Dy-free sintered Nd-Fe-B magnets with higher coercivity can be prepared by further refining the grain size to submicron scale. The hydrogenation disproportionation desorption recombination (HDDR) process can be used to manufacture Nd 2 Fe 14 B magnetic powders with sub-micrometer grains. Single grain HDDR powders with the mean size of 300 nm is recommended as starting materials of fabricating fine-grained sintered magnets[3], but it is hard to obtain single grain HDDR powders by conventional jet milling technique. In this paper, highly textured HDDR Nd-Fe-B powders with uniform thin Nd-rich grain boundary layers were prepared. The detailed microstructure and magnetic properties of the powders were analyzed. We think that the highly anisotropic HDDR powders can be used to prepare fine-grained sintered magnets by conventional jet milling technique and sintering process.