Simultaneous enhancement in coercivity and remanence of Nd2Fe14B permanent magnet by grain boundary diffusion process using NdHx

We have successfully developed a Dy-free grain boundary diffusion process with neodymium hydride (NdHx) alloy to the permanent magnet Nd2Fe14B powders using hydrogenation - disproportionation - desorption - recombination (HDDR) method. All the diffusion treatments were performed at 700 -800 degrees C for various annealing time under the high vacuum with rotating diffusion method that effectively control the abnormal grain growth. The coercivities of Dy-treated Nd2Fe14B powders were varied from 9.5 kOe to 13.2 kOe but the remanence was decreased to 8.1 kG (10% reduction) depending on dysprosium hydride (DyHx) content and diffusion treated time. However, the coercivity and remanence of Dy-free diffusion treated powder have been increased to 12.2 kOe (28.5% enhancement) and 11.1 kG (22% enhancement) at the optimal diffusion treatment (-800 degrees C for 3 h), respectively. This unique simultaneous enhancement is to isolate the magnetic coupling between Nd2Fe14B grains by creating nonmagnetic Nd grain boundaries and enhance the alignment of the Nd2Fe14B hard magnetic phase, fabricated by optimal diffusion conditions. (C) 2015 Elsevier B.V. All rights reserved.