Coercivity variations with Pr- and Zr-substituted NdDyFeB-based HDDR powders

As part of an industry-based project. we studied the effects of Pr and Zr substitutions to a basic Nd15DyFe76B8 material. We processed the materials using a conventional hydrogenation-disproportionation-desorption-recombination (HDDR) process and a simple rotary-pump vacuum; however. we also experimented with high-vacuum conditions in order to see what effect these had. The Pr and Zr substitutions were observed to have a positive and cost-effective influence on the coercivity of the processed powders: the optimum Pr substitution was the replacement of three-quarters of the neodymium, and for Zr. a much smaller 0.1 at % was found to be the best. Microstructural observations of the as-cast structures revealed significant differences between the Zr- and Pr-substituted materials and the additive-free NdDyFeB alloy, but post-HDDR microstructures were all very similar and provided little help for optimizing the processing conditions. By combining the substitutions of Pr and Zr in a relatively rare-earth-rich alloy, we were able to produce a coercive powder of > 1000 kA/m and have a process which can now be quickly and easily transferred to the factory. (C) 2001 Elsevier Science B.V. All rights reserved.