Effect of Nd content on the microstructure and coercivity of hot-deformed Nd–Fe–B permanent magnets

The microstructure of hot-deformed Nd–Fe–B permanent magnets with different Nd contents was investigated in order to correlate them with the hard magnetic properties. A thick distinct Nd-rich grain boundary (GB) layer was observed in a high Nd content sample by scanning electron microscopy and transmission electron microscopy. Three-dimensional atom probe results showed a significant increase in the Nd content in the GB as the overall Nd content in the alloy increased. We found a clear correlation between the Nd concentration in the GB layer and the coercivity. The mechanism of the coercivity increase is discussed based on the microstructure characterization and micromagnetic simulation results.