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)32.5Fe62.0Cu5.5 and low-melting-point Dy71.5Fe28.5, 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.