Grain boundary restructuring and La/Ce/Y application in Nd-Fe-B magnets

Since the 1980s,Nd-Fe-B with largest energy product (BH)_max approaching the theoretical limit has become the landmark of permanent magnetic material.The application spectrum for Nd-Fe-B continues to expand over time both in the industrial and commercial sectors,which leads to growing research interests for solving the long-standing drawbacks of Nd-Fe-B,i.e.,poor corrosion resistance,low coercivity,high Dy/Tb and low La/Ce/Y consumption.Concerning the above obstacles,we aim to present the novel grain boundary restructuring (GBR) approach,from GB design,processing,to structure evolution and property evaluation with a focus on the corrosion and coercivity mechanism of the restructured 2:14:1-typed magnets.Starting with an introduction to the fundamental of GBR,two representative examples,high-electrode-potential (Pr,Nd)_32.5Fe_62.0Cu_5.5 and low-melting-point Dy_71.5Fe_28.5,are given with detailed descriptions of the advantages of GBR to enhance the intrinsic anti-corrosion stability and to strengthen the coercivity at low Dy consumption.Microstructure-property correlations are established to understand the critical importance of regulating the restructured GB phase to maximize the all-round performance of the 2:14:1-typed permanent magnets.Aiming at sustainable and balanced development of rare earth (RE) industry,the proceeding section proposes new prototypes of La-Ce and Y-Ce co-substitutions with dual benefits of stabilizing the 2:14:1 tetragonal phase and strengthening the intrinsic hard magnetism.The findings of additional REFe₂ intergranular phase delight that the GBR approach also opens up a new horizon of research and application to develop high-performance La/Ce/Y-rich permanent magnets with deliberately tailored GB phase.