Effect of Heterogenous Gradient Structure Induced by High Cu Content on Nanocrystallization Process and Magnetic Properties of Fe‐Based Nanocrystalline Alloys

ABSTRACT The pre‐existing α‐Fe crystals have important effects on the precipitation and growth of nanocrystals and finally determine the comprehensive soft magnetic properties (SMPs) of the nanocrystalline alloys (NAs). In this work, a high content of Cu elements has been added to Nanomet‐type alloys to enhance the gradient heterogeneity in order to well control the nanocrystalline process of amorphous alloys. Crystallization kinetics reveal that α‐Fe crystals in the free‐side layer exhibit higher nucleation and growth activation energies, leading to a slower crystallization rate than in the wheel‐side layer. This inhomogeneous crystallization behavior reduces the uneven distribution of α‐Fe crystals in the as‐spun high Cu content ribbons. Consequently, the Fe 82.5 Si 3.5 B 9 P 2 C 1 Cu 1.7 alloy achieves superior SMPs through nanocrystallization, including high B s (∼1.82 T), low H c (< 10 A m −1 ), and high μ e (> 10,000 @ 1 kHz) across wide T A and t A ranges. Compared to low‐temperature long‐time and low‐temperature short‐time heat treatments, high‐temperature short‐time heat treatment results in better SMPs. This is because it intensifies the competition between the fast nucleation/growth of new α‐Fe crystals and the slower growth of pre‐existing crystals. These findings deepen the understanding of crystallization processes in gradient inhomogeneous materials and guide the optimization of annealing processes for improved performance in Fe‐based NAs.