Grain size dependence of coercivity of hot-deformed Nd-Fe-B anisotropic magnets

The dependence of the coercivity of hot-deformed anisotropic Nd-Fe-B magnets on grain size has been studied by processing the magnets at different temperatures. Higher coercivity was obtained in fine-grained magnets processed at lower temperature (700 °C), in which intergranular phases formed uniformly along the grain boundaries. On the other hand, large Nd-rich triple-junction phases were frequently observed in the larger grain-sized magnets processed at higher temperature (900 °C). Three-dimensional atom probe analyses showed that the Nd content in the intergranular phase decreased as the processing temperature increased. The origin of the coercivity difference in these hot-deformed magnets processed at different temperatures is discussed based on micromagnetic analysis of the observed microstructures complemented with finite-element micromagnetic simulations.