Abstract:The effects of adding 1at% early transition metals (M=Ti, V, Cr, Zr, Nb, Mo) on the melt-spun structure, crystallized microstructure, and magnetic properties of Fe84.5B13Cu1.5M1 alloys were investigated. The mechanisms of different M elements in regulating the alloy structure and magnetic performance were also discussed. Results show that except for the M=Zr alloy presenting fully amorphous state in the as-spun condition, other alloys all contain pre-existing α-Fe grains dispersed in amorphous matrix with average grain sizes (dα-Fe) smaller than 10 nm and high numerical density (Nd). M doping can reduce both Nd and dα-Fe of pre-existing α-Fe phases to varying degrees, with reduction effectiveness following the sequence: Cr<V<Mo<Nb<Ti<Zr. This trend positively correlates with the enhanced amorphous-forming ability derived from increased atomic size mismatch and negative mixing enthalpy induced by M elements. M doping significantly influences the α-Fe phase/amorphous-nanocrystalline composite structure and magnetic properties after heat treatment. Compared with Fe85.5B13Cu1.5 alloy, alloys with M=V/Cr/Nb/Mo exhibit reduced average grain size (Dα-Fe) and coercivity (Hc) of α-Fe, while alloy counterparts with M=Ti/Zr show increased Dα-Fe and Hc. All doped alloys demonstrate slightly decreased saturation magnetic induction (Bs). Notably, the Mo-doped alloy achieves optimal nanocrystalline structure and soft magnetic properties, showing Dα-Fe=14.9 nm, Hc=8.3 A/m and Bs =1.84 T, which significantly outperforms the results as 17.9 nm, 22.1 A/m and 1.90 T of reference alloy, respectively. Mo doping attains optimized matching between Nd and dα-Fe of pre-existing α-Fe grains in melt-spun alloys, which enhances the coordinated intergranular competitive growth effects during thermal crystallization. This mechanism effectively refines the nanocrystalline structure, reduces magnetocrystalline anisotropy, and consequently improves soft magnetic properties.