Processed by the hydrogenation, disproportionation, desorption and recombination (HDDR) process

Abstract

The hydrogenation, disproportionation, desorption and recombination (HDDR) process has been employed to produce -based permanent magnets. The master alloys for HDDR are -based alloys which are obtained by annealing mechanically alloyed (MA) powder at . The disproportionation reaction at results in the formation of an intimate mixture of Nd-hydride, and . On desorbing the hydrogen at the same temperature, different constituents recombine to form the thermodynamically stable and the Nd-rich phase, depending sensitively on recombination time and slightly on hydrogenation time. The phases obtained by HDDR at consist of , the Nd-rich phase and , whereas those obtained at are of , the Nd-rich phase and a small amount of . For comparison, the -based alloys have also been processed by HDDR, in which more and Nd-rich phases are found to coexist with after recombination at the same temperature. The -based alloy made by MA in conjunction with HDDR has better magnetic properties than that made by MA only.