科研之友
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摘要
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)(17)Fe75Si3B6 (x = 0-0.6) alloys prepared by melt spinning and observed an unusual chemical heterogeneity in the (Ce0.5Y0.5)(17)Fe75Si3B6 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 H-c of 432 kA m(-1) and a greatly enhanced maximum energy product (BH)(max) of 7.1 MGOe with Curie temperature T-c of 547 K were obtained. In the alloys with x = 0.1-0.4, H-c decreased with Y substitution but the remanence J(r), (BH)(max) and T-c did not increase significantly despite the higher magnetization M-s and T-c 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 J(r) was obtained, (BH)(max) value of 7.2 MGOe was similar to that of the alloy with x = 0.5 because H-c 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.
