Mechanical strength of the solid-HDDR treated Nd–Fe–B-type materials

The hydrogenation, disproportionation, desorption, recombination (HDDR) is known as a unique process through which a noncoercive cast Nd–Fe–B-type material can be easily converted into a coercive one. Although the conventional HDDR process generally leads to a powderlike material, a solid-HDDR material can be realized if the HDDR process is properly modified (solid-HDDR). In the present study, the change of mechanical strength (compressive strength) of the Nd–Fe–B-type material during the solid-HDDR has been investigated using a sintered magnet with composition Nd13.8Dy0.7Fe78.25Si0.15Mn0.6B6.5. It has been found that the low strength of the hydrided material was improved by the subsequent disproportionation. The restoration of the strength was explained by the eutectoidlike disproportionation structure containing fine neodymium hydride rod embedded in tough iron matrix. The high strength of disproportionated material was reduced radically in an earlier stage of recombination, and this was explained by th...