Coercivity enhancement of Nd-Fe-B sintered magnets with intergranular adding (Pr, Dy, Cu)-H_x powders

Forming Nd₂Fe₁₄B/(Nd, Dy)₂Fe₁₄B core-shell structure by intergranular adding Dy-containing sources into Nd-Fe-B sintered magnets is effective to improve coercivity and to minimize remanence loss simultaneously. However, the excessive Dy located in the intergranular regions has nearly no hard magnetic contribution, causing its low utilization efficiency. In this work, diluted Dy powders (Pr₃₇Dy₃₀Cu₃₃)-H_x were prepared and incorporated into Nd-Fe-B sintered magnets via a dual-alloy approach. The coercivity increases rapidly from 15.0 to 18.2 kOe by 21.3% with 2.0 wt% (Pr, Dy, Cu)-H_x addition (the equivalent Dy is only 0.32 at%). The deduced coercivity incremental ratio is 10.0 kOe per unit Dy at%. Dehydrogenation reaction of (Pr, Dy, Cu)-H_x occurs during sintering, which favors Dy diffusion towards the 2:14:1 phase grains as well as smoothing the grain boundaries (GBs). The enhanced local anisotropic field and the well decoupled 2:14:1 phase grains contribute to such rapid coercivity enhancement. This work suggests that adding diluted Dy hydrides is promising for fabricating high coercivity Nd-Fe-B sintered magnets with less heavy rare-earth consumption.