PrAl and PrDyAl diffusion into Nd-La-Ce-Fe-B sintered magnets: Critical role of surface microstructure in the magnetic performance

摘要

To solve the challenging hurdle of low coercivity, Pr80Al20 and Pr40Dy40Al20 diffusion is applied to the Nd-La-CeFe-B sintered magnets with high La-Ce substitution (La-Ce/TRE = 40 wt%, TRE: total rare earth). Coercivity approaching 15 kOe with approximately 200% increment level is acquired for PrAl diffusion. Anomalously, PrDyAl diffusion cannot further enhance the coercivity whilst lowers the remanence drastically from 12.60 to 12.16 kG. This anomaly is correlated with the critical role of surface microstructure that consumes large amounts of expensive Dy, i.e. thick Dy/Fe-rich top layer, and below that Dy/Al diffusion into the interior of 2:14:1 grain. Such predominant Dy agglomeration at the surface region can well interpret that the negative role of Dy in deteriorating remanence is exacerbated, while its positive role in strengthening the local shell of 2:14:1 phase and enhancing the coercivity is weakened. Comparably, PrAl diffusion generates the Pr-rich magnetically hardening shell along the continuous grain boundary layer, paving it a versatile route for significant coercivity enhancement of Nd-La-Ce-Fe-B without sacrificing remanence.