Optimization of crystallization behavior and soft magnetic properties of the Si-free Fe-B-P-C-Cu nanocrystalline alloys by Cu content tuning

•Effect of Cu on the AFA, structure and SMPs of Fe-B-P-C-Cu alloys are studied.•The stability of α-Fe phase can be improved by tuning Cu.•The sensitivity of SMPs to annealing temperature can be optimized by tuning Cu.•Fe82.9B9P3C4Cu1.1 alloy exhibits Bs of 1.84T~1.85T and Hc of 13.0A/m ~ 8.9A/m. The effect of Cu content on amorphous forming ability (AFA), crystallization behavior and soft magnetic properties of the new Si-free Fe84-xB9P3C4Cux (x = 0.7, 0.9, 1.1, 1.3 and 1.5) alloys were systematically investigated. The phase structure identified by XRD reveals that the alloys for Cu content less than 1.3 at. % have good AFA. The dependence of activation energies of nucleation and growth on Cu content shows that the growth of α-Fe grains is more difficult than the nucleation for the alloy ribbons with Cu ≤ 1.1 at. %, which is beneficial to obtain finer nanocrystalline α-Fe grains during crystallization annealing, while for those with Cu > 1.1 at. %, the growth of α-Fe grains is easier than the nucleation. The relationship between coercivity (Hc) and the annealing temperature (Ta) indicates that appropriate Cu content is beneficial to improve the stability of soft magnetic properties, especially, when annealed near the temperature of the first crystallization peak. The nanocrystalline Fe82.9B9P3C4Cu1.1 alloy exhibits a high saturation magnetic flux density of 1.84 T ~ 1.85 T and a low Hc of 13.0 A/m ~ 8.9 A/m annealed in the range of 703 K ~ 763 K.