Study of the effect of a repeated HDDR treatment on the coercivity oftwo rare-earth-transition metal hard magnetic materials

Abstract

In an attempt to achieve a more complete and more homogeneousrecombination in the hydrogenation, disproportionation, desorption andrecombination (HDDR) of Sm2Fe17-type and Nd-Fe-B-typepermanent magnet alloys, thus achieving high coercivity, an HDDR treatment wasapplied repeatedly to those alloys (the HDDR-treated Sm2Fe17-type alloy was nitrogenated afterwards). The effect of thistreatment on the coercivity was investigated. The hydrogenation anddisproportionation characteristics of the previously HDDR-treated alloys werealso examined. It was found that for the Sm2Fe17-type alloythe hydrogenation temperature was slightly raised as the number of HDDR cyclesincreased, while the disproportionation temperature was significantlydecreased. For the Nd-Fe-B-type alloy both the hydrogenation and thedisproportionation temperatures decreased with the number of HDDR cycles.Repeated HDDR increases the coercivity of both Sm2Fe17Nx-type and Nd-Fe-B-type materials. The increase is greater for the Sm2Fe17Nx-type material.