Enhancement in hard magnetic properties of nanocrystalline (Ce,Y)–Fe–Si–B alloys due to microstructure evolution caused by chemical heterogeneity
Abstract
To release the pressure on the supply of critical rare earths (REs), much effort has been made to substitute Nd and Pr by more highly abundant La, Ce, and Y elements in Nd–Fe–B magnets. The chemical heterogeneity reported in multi-main-phase sintered magnets is a promising solution to suppress the magnetic dilution of La-, Ce-, or Y-added Nd–Fe–B magnets. Here, we investigated the nanocrystalline (Ce1−xYx)17Fe75Si3B6 (x = 0–0.6) alloys prepared by melt spinning and observed an unusual chemical heterogeneity in the (Ce0.5Y0.5)17Fe75Si3B6 alloy. Here, the Y segregation in RE2Fe14B (2 : 14 : 1) phase and Ce segregation in REFe2 (1 : 2) phase were demonstrated due to the significantly different Ce and Y diffusion rates in these two phases. As a result, an extremely high coercivity Hc of 432 kA m−1 and a greatly enhanced maximum energy product (BH)max of 7.1 MGOe with Curie temperature Tc of 547 K were obtained. In the alloys with x = 0.1–0.4, Hc decreased with Y substitution but the remanence Jr, (BH)max and Tc did not increase significantly despite the higher magnetization Ms and Tc of the Y2Fe14B phase than those of Ce2Fe14B. The reason for this could be attributed to the formation of a large amount of 1 : 2 phase and the insignificant Y and Ce segregations. For the alloy with x = 0.6, though a further increase of Jr was obtained, (BH)max value of 7.2 MGOe was similar to that of the alloy with x = 0.5 because Hc was significantly reduced. The unique microstructural evolution was responsible for the notable change in magnetic properties. The nano-level chemical heterogeneity manifested by the present work offers a potential approach to improve the cost performance and understand the physical mechanism of free-RE magnets.