NdDyFeBZr high-coercivity powders prepared by intensive milling and the HDDR process

A comparative study of the processing of highly coercive, isotropic NdFeB-type magnet powders was carried out using two different techniques. Nd Fe B alloys with additions of Dy (1 at.%) and Zr (0.1, 0.3 and 0.7 at.%) were processed by: (a) a combination of 15 77 8 intensive milling-and-annealing and (b) the hydrogenation-disproportination-desorption-recombination (HDDR) process. A marked retarding effect on grain growth due to the Zr addition was observed. Intensively milled and annealed samples containing both Zr and Dy additions showed a large improvement in coercivity in comparison with the additive-free alloys, reaching an optimum value of 2.5 T for 0.1 at.% Zr and 1.0 at.% Dy. The improved microstructure resulted in a wide processing window in which high-coercivity material could be produced. A ZrB lamellar phase was observed using transmission electron microscopy; this phase appears to have a grain-growth- 2 inhibiting effect during HDDR processing of NdDyFeBZr materials. A maximum coercivity of 1.9 T was obtained for the HDDR- processed material. At recombination temperatures above 8008C explosive grain growth was observed using Kerr microscopy. © 2001 Elsevier Science B.V. All rights reserved.