Coercivity Enhancement of Sintered Nd-Fe-B Magnets by Grain Boundary Diffusion with DyH₃Nanoparticles

Abstract

Grain boundary diffusion technique with DyH 3 nanoparticles was applied to fabricate Dy-less sintered Nd-Fe-B permanent magnets with high coercivity. The magnetic properties and microstructure of magnets were systematically studied. The coercivity and remanence of grain boundary diffusion magnet were improved by 60% and reduced by 7% compared with those of the original magnet, respectively. Meanwhile, both the remanence temperature coefficient (α) and the coercivity temperature coefficient (β) of the magnets were improved after diffusion treatment. Investigation shows that Dy is preferentially enriched as (Nd, Dy) 2 Fe 14 B phase in the surface region of the Nd 2 Fe 14 B matrix grains indicated by the remarkable enhancement of the magneto-crystalline anisotropy field of the magnet. As a result, the magnet diffused with a small amount of Dy nanoparticles possesses enhanced coercivity without remarkably sacrificing its magnetization.

Coercivity enhancement of recycled Nd–Fe–B sintered magnets by grain boundary diffusion with DyH3 nano-particles

“…Fig. 1 show the TEM image of DyH 3 nano-particles [8]. Most of DyH 3 nano-particles were 50-100 nm in diameter.…”

“…Recently, many researchers have begun to study on recycling of anisotropic Nd-Fe-B powders and magnets [2][3][4]. In the past few years, new techniques by diffusing a continuous layer of Tb or Dy onto the surface of the Nd 2 Fe 14 B matrix grains have been developed [5][6][7][8]. It allows the enhancement of coercivity without obvious reduction of their remanence.…”

Waste Nd-Fe-B Sintered Magnet Recycling by Doping With Rare Earth Rich Alloys

“…The B r is never fully recovered to the original level of the starting material. It is expected that the Dy in the SA alloy powder substitutes some of Nd in the Nd 2 Fe 14 B main phase and forms (Dy, Nd) 2 Fe 14 B phase [10], [11], which has a lower M s and higher H A than that of the Nd 2 Fe 14 B phase [12], [13]. The additional decrease in the B r with SA content above 2.0 wt% can be attributed to the formation of the (Dy, Nd) 2 Fe 14 B phase.…”

Review on the Parameters of Recycling NdFeB Magnets via a Hydrogenation Process

“…The same as the primary production of NdFeB magnets, the key to the recovery of magnetic properties of recycled NdFeB magnets is rooted in doping with REE hydrides . Liu et al reported that by adding up to 1% of nanoparticles DyH 3 before sintering about 89% of the initial ( BH ) max can be recovered.…”