Modified HDDR procedures applied to NdFeB alloys

The magnetic properties of Nd16.2Fe78.2B5.6, Nd12.6Fe81.4B6.0, and Nd12.6Fe69.4Co11.0Ga1.0B6.0 alloys after the application of modified HDDR (hydrogenation-disproportionation-desorption-recombination procedures have been investigated and particular emphasis has been given to the development of magnetic anisotropy and high coercivity in these different types of materials. Conventional HDDR processing leads to anisotropic material only in the case of the Nd12.6Fe69.4Co11.0Ga1.0B6.0 alloy. Combining solid-disproportionation with a controlled recombination under partial hydrogen pressure at 900 degrees C, a significant degree of anisotropy and a good coercivity were achieved for the two ternary alloys. These findings indicate the possibility of more than one mechanism and the relevance of the rod-like solid-disproportionated structure for the inducement of anisotropy. Another modification of the standard procedure, the reactive milling technique, leads to isotropic Nd16.2Fe78.2B5.6 powder with grain sizes, both in the disproportionated and recombined states, significantly smaller than those of conventional powder and a very high coercivity of mu(0J)H(c)=1.88T.