Overview of the Ways for Enhancing the Coercivity of Hot-Deformed Nd2Fe14B-Type Magnets

Several ways for improving the coercivity of the hot-deformed NdFeB magnets, mainly made from commercial MQU-F powders, were explored. First, mixing another commercial Dy-containing MQU-G powders into MQU-F powders could enhance the coercivity of the hot-deformed magnets from 15.1 to 22.1 kOe. The increment of magnetocrystalline anisotropy field for R
₂
Fe
₁₄
B with Dy substitution leads to coercivity enhancement. In addition, doping 2 wt% R70Cu30 alloy powders [R = Dy, Dy + Nd, mischmetal (MM)] into the hot-deformed NdFeB magnets is also effective in enhancing the coercivity to 19-19.5 kOe, originated from different mechanisms. Dy
₇₀
Cu
₃₀
-doped magnets and (Nd
_0.5
Dy
_0.5
)
₇₀
Cu
₃₀
-doped magnets show an almost identical enhancement of coercivity of about 4.4 kOe. Importantly, the latter magnet shows a beneficial effect of reducing the usage of Dy from 1.6 to 0.8 wt%. Most interestingly, Dy-free MM
₇₀
Cu
₃₀
-doped magnet (MM = Pr
₇₁
Nd
₂₇
Ce
₂
) can also exhibit a comparable coercivity increment of about 4 kOe and yet still persist high magnetic energy product. The microstructure analysis shows that the entrance of Pr into 2:14:1 phase, grain refinement, modified grain shape, and Ce-containing grain boundary layer play crucial roles in its coercivity enhancement.