材料期刊网

The hydrogenation, disproportionation, desorption and recombination (HDDR) process has been employed to produce Nd2Fe14C-based permanent magnets. The master alloys for HDDR are Nd2Fe14C-based alloys which are obtained by annealing mechanically alloyed (MA) Nd16Fe75C9 powder at 850 degrees C. The disproportionation reaction at 850 degrees C results in the Formation of an intimate mixture of Nd-hydride, alpha-Fe and Nd2Fe2C3. On desorbing the hydrogen at the same temperature, different constituents recombine to form the thermodynamically stable Nd2Fe14C and the Nd-rich phase, depending sensitively on recombination time and slightly on hydrogenation time. The phases obtained by HDDR at 950 degrees C consist of Nd2Fe17Cx, alpha-Fe, the Nd-rich phase and Nd2C3, whereas those obtained at 700 degrees C are of Nd2Fe17Cx, the Nd-rich phase and a small amount of alpha-Fe. For comparison, the Nd2Fe17Cx-based alloys have also been processed by HDDR, in which more alpha-Fe and Nd-rich phases are found to coexist with Nd2Fe14C after recombination at the same temperature. The Nd2Fe14C-based alloy made by MA in conjunction with HDDR has better magnetic properties than that made by MA only.