Development of high-coercivity nanocomposite permanent magnets based on Nd2Fe14B and FexB

In a composition range along the tie line between Fe3B and Nd2Fe14B with Nd concentration between approximately 6 and 9 at%, it has been found that addition of a few atomic percent of Ti suppresses formation and growth of γ-iron and promotes the formation of Nd2Fe14B. This lead to development of a new series of nanocomposite permanent magnet materials on the Nd–Fe–B–Ti–C system, for which the strip-casting technique can be applied in the rapid solidification process. The newly developed Nd–Fe–B–Ti–C nanocomposite permanent magnets cover a wide range of magnetic properties and include a high-coercivity grade with coercivity (HcJ) of about 1 MA/m and remanence (Br) of 0.8 T and a high-remanence grade with HcJ = 500 kA/m and Br = 0.86 T. The high coercivity owes its origin to a larger volume fraction of the hard magnetic Nd2Fe14B phase compared to the previous Fe3B/Nd2Fe14B nanocomposite permanent magnets in which the volume fraction of the Nd2Fe14B phase is limited by disappearance of this phase in Nd concentration range beyond about 5 at%. Resin-bonded magnets fabricated using these powders show excellent stability against oxidation under a humid, high-temperature atmosphere.