Abstract: The Fe_81.3Si₄B_13-xP_xCu_1.7 soft magnetic alloys with high Cu and proper P elements addition were synthesized with the aim of ensuring the amorphous forming ability (AFA) while expanding the crystallization window (CW). It is found that the atomic ratio of P/Cu of ∼3 is advantageous for AFA whereas a small amount of P addition promotes the precipitation of α-Fe grains and excessive P addition induces surface crystallization behavior of the present alloys. High Cu concentration can expand the annealing temperature (T_a) window whereas proper P addition effectively expands the annealing time (t_a) window. The Fe_81.3Si₄B₈P₅Cu_1.7 soft magnetic alloy was successfully synthesized with a large T_a window of up to 130 °C and t_a window of 90 min, which is a breakthrough for nanocrystalline alloys with high saturation magnetization. Microstructure analysis reveals that the ultra-wide CW is related to the unique nucleation mechanism, that is, the α-Fe grains are precipitated attaching to the Cu or CuP clusters and enveloping the Cu clusters, resulting in the high number density of α-Fe nanocrystals. The ultra-wide CW promises the potential material in flexibly choosing the annealing process according to the performance.

Key words: Nanocrystalline alloys, Amorphous forming ability, Crystallization window, Soft magnetic properties