An improved HDDR treatment for the production of anisotropic Nd-Fe-B ternary powders

The magnetic properties of Nd12.2Fe81.8B6.0 alloys processed using a new HDDR (hydrogenation disproportionation desorption recombination) treatment were investigated. This newly proposed HDDR treatment is a combination of heat treatments at hydrogen pressures close to the recombination pressure of the Nd2Fe14B compound, in both the disproportionation and recombination stages. In other words, this new treatment is a combination of the I-HD (heating in a low H-2 pressure during the hydrogenation disproportionation stage.), and s-DR (heating in Ar or in a relatively high pressure of hydrogen, at the start of recombination) treatments. In this investigation, the influence of the s-DR conditions on the magnetic properties of anisotropic Nd-Fe-B HDDR-treated powders, were investigated. It was found that an s-DR treatment in which the hydrogen pressure was decreased in steps from 0.1 MPa to 0.5 kPa, enhanced the remanence (1.45 T) and anisotropy (Br/Js=0.94). The rate at which the hydrogen pressure decreases to 6 kPa during s-DR is also considered to be an important factor in obtaining both a high remanence and a high coercivity. In addition, the coercivity was found to increase after an s-DR treatment in which the temperature was decreased in a step by step manner. (C) 2002 Elsevier Science B.V. All rights reserved.