Production of Nd-Fe-Co-B Magnet Powders Having High B_r by Modified HDDR Process

Abstract

It is well established that the hydrogenation-decomposition-desorption-recombination (HDDR) process can produce anisotropic Nd₂Fe₁₄B-based magnet powders having high coercivities. In this study, we investigated effects of the intermediate argon (IA) treatment, where alloys are annealed under argon atmosphere after hydrogenation in the HDDR process, on magnetic properties of Nd_12.6Fe_bal.Co_17.4B_6.5Zr_0.1Ga_0.3 magnet powders. It was found that magnetic anisotropy of magnet powders is improved with IA treatment time. On the other hand, their coercivities are decreased by the IA treatment longer than 10min. The magnetic properties of the magnet powders with diameters of 100-212μm produced through the IA treatment for 10min are as follows: B_r=1.38T, H_cJ=1000kA/m and (BH)_max=334kJ/m³. Transmission electron microscope observation revealed that change in microstructures such as rapid growth of α-(Fe, Co) matrix, disappearance of (Fe, Co)₂B and formation of a new phase (TE phase) occur in hydrogenated alloys during the IA treatment.