Thermal stability improvement of hot-deformed PrNd-Fe-B magnets by diffusion of Nd-Gd-Ga alloy

This work introduces a novel approach by combining liquid and hard phases during deformation using a single alloy. The hot-deformed Nd-Fe-B magnets with notable thermal stability were achieved through diffusion of Nd-Gd-Ga alloy. The uniform microstructure of the matrix phase, the magnetic isolation effect of the non-ferromagnetic grain boundary phase and the increase in Curie temperature of the matrix phase played a key role in enhancing thermal stability. The effective remanence temperature coefficient α has increased from −0.152 %/℃ to −0.133 %/℃, and the coercivity temperature coefficient β has increased from −0.490 %/℃ to −0.430 %/℃ within the temperature range from 20 to 180 ℃. The irreversible magnetic flux loss of magnets shows a reduction of 95.93 % at 180 ℃. The diffusion by Nd-Gd-Ga alloy suppresses the growth of coarse grains, thereby improving the squareness. The formation of non-ferromagnetic grain boundary phases enhanced the intrinsic coercivity and inhibited further grain growth. The emergence temperature of reverse magnetization domains has risen from 80℃ to 110℃, with distinct changes in their expansion pattern, indicating that the refined structure impedes their nucleation and growth. Simultaneously, the Gd element which entered matrix phase resulted in the increase of Curie temperature , thereby enhancing thermal stability. A novel low-cost diffusion strategy is presented to enhance the thermal stability of hot-deformed Nd-Fe-B magnets. • A diffusion method in hot-deformed PrNd-Fe-B magnets uses a single alloy combining liquid and hard phases during deformation. • The importance of irreversible magnetic flux loss and its influencing factors is emphasized. • Gd, the less common element, is used to boost the Curie temperature of the 2:14:1 phase, enhancing the thermal stability of magnets.