Enlarging heat-treatment processing windows of Fe–Si–B–P–Cu–M nanocrystalline alloys by doping transition metal elements

The crystallization behavior, heat-treatment condition dependences of soft-magnetic properties and microstructural evolution in Fe_83-xSi₄B₁₀P₂Cu₁M_x (M = V, Cr, Nb, Mo, Ta and W; x = 0–2 at%) nanocrystalline alloys were systematically investigated. We found that these transition metals can enlarge the heat-treatment processing window and effectively improve the soft-magnetic properties. According to the results of comparative studies, Ta and Nb are the optimal elements in stabilizing and refining the nanocrystalline microstructure. The order of the alloying effect on the optimal heat-treatment conditions is: Ta=Nb > Mo=W > V > Cr, which can be correlated to the negative mixing enthalpy and atomic size difference between transition element and other component elements. The minor Nb and Ta doped alloys (1 at%) can be annealed in a large window with a temperature range of 70 K and a time range of 60 min, which are readily accepted for the industry. Superior soft-magnetic properties containing high B_s of 1.73 T, H_c of 8.4 A/m and μ_e of 21 × 10³ were obtained in the sample annealed at 743 K in 60 min. These high-performance alloys should be promising candidates for the mass production and the effects of transition metal alloying can be good references for the future development of high B_s alloys.