THE EFFECT OF AGING AT 500-DEGREES-C ON NB-CONTAINING ND-FE-B MAGNETS

The aging behaviors of Nd16.4Fe75.7B7.9, Nd16Fe76.3Nb0.3B7.4, and Nd14.5Dy1.5Fe76Nb1B7 magnets were investigated. The magnets were quenched and then aged at 500-degrees-C to establish whether recovery of coercivity was possible below the melting point of the grain boundary. The samples were cooled and measured magnetically after 10- or 20-min intervals before being heated again for another interval. After aging at 500-degrees-C for 55 min there was a dramatic increase in coercivity in the Nd-Dy-Fe-Nb-B samples, whereas the coercivity of the Nd-Fe-B samples remained unaltered. The results from thermomagnetic analysis on Nd-Dy-Fe-Nb-B show that an extra ferromagnetic phase is present in the magnets that had been aged for over 55 min and in the magnets that had full magnetic properties, but not in the quenched magnets. The Nd-Fe-B samples did not show any additional ferromagnetic phase. The experiments were repeated with Nd-Fe-Nb-B magnets and the results followed the same trend to those observed in the Nd-Dy-Fe-Nb-B magnets. The difference in coercivity between the aged and the initial-state magnets, for all types, was recovered upon heating at 650-degrees-C.