Enhancement of Heat Resistance of Nd-Fe-B Anisotropic Magnet by Dy addition in HDDR Process

摘要

Nd-Fe-B anisotropic bonded magnets have excellent magnetic properties in room temperature, but the application has been somewhat limited due to its low heat resistance. In sintered magnets, it is known that addition of dysprosium to the NdFeB ingot increase its coercivity, which directly brings the improvement of the heat resistance. However this approach showed a little effect on HDDR-method. It is because there exists a difference in hydrogenation pressure between dysprosium and neodymium. The authors have found that the dysprosium addition after the HDDR treatment can avoid the above mentioned problem, and had developed a new process to improve the coercivity of magnet powder. The process is to make dysprosium diffuse into Nd-Fe-B magnet powder by heat-treating the mixture of DyH_2 fine powder and Nd-Fe-B magnet powder produced by the d-HDDR treatment. The magnetic properties of the magnet powder showed (BH)max of as high as 259kJm~-3 and iHc of 1.56MAm~-1. Bonded magnets made from this magnet powder showed the temperature of 5 percent-irreversible loss up to 415K, which is much higher compared to the temperature of 353K obtained for the dysprosium-less magnet.