An insight into the improved microstructure and elevated comprehensive properties of sintered Nd-Fe-B magnets via the infiltration of DyCu alloy

Grain boundary diffusion (GBD) can maximize the utilization of heavy rare earth (HRE) elements, and achieve the purpose of greatly improving the coercivity without reducing the remanence and maximum magnetic energy product. In this work, based on GBD technique, high coercivity Nd-Fe-B magnets are produced by using Dy30Cu70 alloy as the diffusion source. The results show that, with increasing diffusion temperature, the coercivity is enhanced monotonously from 1103 kA/m for as-prepared magnet to 1428 kA/m for diffusion magnet processed at 900 °C, increasing by 29.5%, and the remanence is decreased slightly. Microstructural characterization reveals that the GBD does not change the crystal structure of intergranular phase. Dy has diffused into matrix phase to form the (Nd, Dy)2Fe14B shell with a higher magnetocrystalline anisotropy field in the extended layer of matrix phase, inhibiting the nucleation of reversed magnetic domain. Cu is mainly enriched in RE-rich phase, which is responsible to the formation of thin RE-rich phase and can effectively increase magnetic isolation effect between matrix phases. Thus, the optimization of the intergranular phase and the formation of (Dy, Nd)2Fe14B shell should be responsible to the huge improvement of coercivity. In addition, the diffusion of DyCu alloy is beneficial in enhancing the thermal stability and corrosion resistance.