A study on magnetic anisotropy induced in the HDDR process

An investigation into the effect of Zr addition and Co and Ni substitution in Nd2Fe14B-based alloys, on an anisotropy induced during the HDDR process, has been undertaken. Experiments were developed to observe the microstructure under polarised light. Magnetisation measurements to determine the orientation of the grains in the Nd2Fe14B phase both in initial ingots and in HDDR treated samples, and thermopiezic analysis to investigate the stability of the Nd2Fe14B phase against disproportionation have been carried out. From the hydrogen absorption and desorption behaviour of both Zr and Co substituted Nd-Fe-B alloys, these elements enhance stability of the 2-14-1 phase against hydrogen. Anisotropic orientation of grains in HDDR treated samples was found to arise from the presence of undisproportionated cells formed by substitutional element, such as Zr and Co. These cells could remain during the disproportionation reaction, and maintain the same orientation as the initial large Nd2Fe14B grains in the recombination reaction, consequently yielding anisotropic HDDR powders. (author)