Magnetic Properties and Stabilities of (Nd_0.76, Pr_0.24)-Fe-B HDDR Powders and Injection-Molded Bonded Magnets Made from Them

Abstract

The effects of replacing Nd by rare-earth mixture Nd_0.76Pr_0.24, which is equivalent to didymium, and hydrogen desorption rate at the early stage of desorption-recombination process on magnetic properties of HDDR Nd-Fe-B powders were studied. It was found that the Pr-substituted powder produced by a very slow desorption speed exhibits the same coercivity H_cJ and approximately 8% higher remanence B_r compared with the powder of pure Nd system prepared by the conventional desorption speed. Although corrosion resistance of the Pr-substituted powder is slightly inferior to that of the pure Nd system powder, it was confirmed that the Pr substitution does not strongly affect irreversible flux losses of the injection-molded bonded magnet fabricated from the powder after exposure to air at 100°C. These results indicate that didymium can be used as an alternative of the pure Nd to produce the HDDR powders. It is also expected that the usage of didymium can reduce the material cost eliminating the process for the separation of the rare-earth elements.