Dependences of magnetic performance and microstructure on the PrGa diffusion time for multi-main-phase Nd-La-Ce-Fe-B magnet

For the multi-main-phase (MMP) Nd-La-Ce-Fe-B magnets with 40% La–Ce substitution level of total rare earth (RE), dependences of the magnetic performance and microstructure on the Pr80Ga20 diffusion time are investigated. Compared to the untreated magnet with low coercivity of 5.2 kOe, the coercivity of PrGa diffused magnet increases to 13.4 kOe after 4 h diffusion, peaks at 16.1 kOe after 6 h diffusion, and then deteriorates after 8 h diffusion. Results show that longer diffusion duration increases the diffusion depth of Pr and Ga, which promotes the formation of non-ferromagnetic RE6Fe13Ga as continuous grain boundary phase, and is beneficial for the coercivity enhancement. However, longer diffusion duration also leads to the homogenization of RE distribution within the matrix phase grains, which weakens the magnetic hardening effect of Pr/Nd-rich shell, and is negative for the coercivity enhancement. Above findings reveal that balancing the microstructure and chemical heterogeneity is important for fabricating high-performance diffusion processed MMP Nd-La-Ce-Fe-B magnets.