Effects of grain size, Cu addition, and Nd substitution for Pr on intrinsic coercivity in cast–hot-pressed Pr-Fe-B magnets

Abstract
The coercivity of anisotropic cast–hot-pressed Pr19Fe74.5B5Cu1.5 magnets is investigated. The microstructure features and virgin magnetization curve reveal a nucleation-controlled coercivity mechanism. Regression analysis shows that the intrinsic coercivity varies inversely as the logarithm of the average grain size: iHc(kOe) = 21.7550 − 6.0517 ln d (μm), which is in good agreement with the nucleation statistical model. Investigation of Cu addition and Nd substitution shows that Cu mainly plays a role of suppressing grain growth during the final annealing. Higher coercivity is thus obtained with Cu addition. Nd19Fe74.5B5Cu1.5 magnets exhibit a much lower coercivity due to their coarse-grained cast structure.