Heat treatment, microstructure and coercivity of (Nd, Dy)-Fe-B based permanent magnets

The mechanism of intrinsic coercive force changes in sintered and annealed (Nd, Dy)-Fe-B magnets has been analyzed. The influence of both the composition and annealing parameters on Hci was considered. The variation of Hci(y) of sintered magnets can be explained in terms of 'magnetic hardening' of (Nd1-yDyy)2Fe14B phase. The reason of annealing enhancement of Hci is 'magneto-structural hardening' caused by microstructural changes within the intergranular Nd-rich regions. The phenomenon of 'magneto-structural hardening' is reversible. Its mechanism is explained by using metastable Nd-Fe phase diagram