Coercivity enhancement of Nd–Fe–B sintered magnets with intergranular adding (Pr, Dy, Cu)−Hx powders

• (Pr, Dy, Cu)–Hx hydride powders were introduced into Nd–Fe–B sintered magnets.
• Rapid coercivity enhancement from 15.0 kOe to 18.2 kOe with only 0.32 at% Dy was realized.
• High utilization efficiency of Dy was achieved due to its promoted diffusion process.
• Wettability and mobility of grain boundary phase was improved.

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)–Hx 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)–Hx 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)–Hx 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.