Microstructure and Coercivity of Tb4O7 Grain Boundary Diffusion Processed Sintered (Nd, Dy)-Fe-B Magnets

摘要: In the grain boundary diffusion (GBD) process of Nd-Fe-B magnets, heavy rare earth elements (HREs) such as Dy and Tb are incorporated preferentially along the grain boundaries, instead of alloying them into the bulk. This results in a dramatic improvement in coercivity without losing remanence, leading to substantial savings in HREs. 1-3 However, it is well known that the alloying of Dy to the matrix is required to attain the coercivity higher than 2 T. In this study, a detailed microstructural characterization was carried out on terbium fluoride GBD processed (Nd, Dy)-Fe-B sintered magnets with four different Dy contents in order to understand the combined effect of Dy alloying and Tb GBD process. The nominal Dy compositions of the four base-alloys (prepared by two-alloy method) were 0, 2, 5, and 11 wt.%. Coercivity values of the four magnets before and after GBD process are, 1.2 and 1.9 T, 1.5 and 2.4 T, 2.1 and 3 …