Microstructure and magnetic properties of anisotropic Nd–Fe–B magnets prepared by spark plasma sintering and hot deformation

Abstract

Bulk anisotropic Nd–Fe–B magnets were prepared from hydrogen–disproportionation–desorption–recombination (HDDR) powders via spark plasma sintering (SPS) and subsequent hot deformation. The influence of sintering temperature on the structure and magnetic properties of the spark plasma sintered Nd–Fe–B magnets were studied. The remanence Br, intrinsic coercivity Hcj, and the maximum energy product (BH)max, of sintered Nd–Fe–B magnets first increase and then decrease with the increase of sintering temperature, TSPS, from 650 °C to 900 °C. The optimal magnetic properties can be obtained when TSPS is 800 °C. The Nd–Fe–B magnet sinter treated at 800 °C was subjected to further hot deformation. Compared with the starting HDDR powders or the SPS treated magnets, the hot-deformed magnets present more obvious anisotropy and possess much better magnetic properties due to the good c-axis texture formed in the deformation process. The anisotropic magnet deformed at 800 °C with 50% compression ratio has a microstructure consisting of well aligned and platelet-shaped Nd2Fe14B grains without abnormal grain growth and exhibits excellent magnetic properties parallel to the pressing axis.