Influence of Cu Addition on Magnetic Properties and Microstructure of Melt-spun NdFeB Alloys

Abstract

The (Nd_10.23Pr_2.56Fe_69.77Co_11.63B_5.81)_100−xCu_x (x = 0–2.0) alloy ribbons were fabricated by melt-spinning technique at 15 m/s, and their hard magnetic performance and microstructure were systematically examined. The experimental results indicate that the intrinsic coercivity (H_ci) initially increases significantly with minor Cu addition, followed by a gradual decrease at higher Cu contents, while both the remanence (B_r) and maximum magnetic energy product ((BH)_max) exhibit a declining trend. Notably, the x = 0.5 alloy achieves the highest intrinsic coercivity of 1260 kA/m, representing a 40.6% improvement compared to the Cu-free alloy. Cu addition results in a marked increase in the grain size. Transmission electron microscopy (TEM) analysis shows that a minor Cu addition has a dramatic effect on the average grain size, enlarging it from 19 ± 1 nm (x = 0) to 60 ± 1 nm (x = 0.5). The mechanism of coercivity improvement induced by Cu addition is discussed by the observed intergranular phase. A distinct ferromagnetic intergranular phase enriched in Nd, Pr, and Cu is observed in the x = 0.5 alloy. The ~ 8 nm-thick intergranular phase exceeds the ferromagnetic exchange interaction length (over 4.18 nm) between 2:14:1 grains, thereby weakening ferromagnetic exchange coupling interaction and enhancing coercivity.