Effect of Fe/Co ratio on the microstructure and properties of a typical FeCo-based amorphous alloys

In this current study, the effect of various Fe/Co ratios on microstructure, thermal stability, microhardness, corrosion resistance and soft magnetic properties of Fe_xCo_{72- x}Y₃Si₁₀B₁₅ (x = 8, 12, 18, 24 and 36 at.%) amorphous alloy ribbons was investigated. Due to the similar atomic radii of Fe and Co ferromagnetic elements, we have prepared a series of glassy alloy ribbons with different Fe/Co ratios through single roller melt-spinning method and have determined their phase structures, thermal stability, microhardness, soft magnetic and anti-corrosion properties. Results present that the alloy ribbons with 36 at.% Fe can maintain fully amorphous state, while there are not only broad peaks at about 2θ = 45° but also sharp crystallization peaks at 2θ = 66° existing for the other four ribbon samples. The thermal stability of alloy ribbons gradually increases with the augmentation of Fe content. The maximum crystallization onset temperature under the heating condition of 20 K/min is about 911.0 K for Fe₃₆Co₃₆Y₃Si₁₀B₁₅ alloy specimen. The average microhardness of these amorphous ribbons in as-spun state and after immersed in 3.5 wt% NaCl solution for 30 h can be up to 1567 HV_0.1 and 1147 HV_0.1 or above, respectively. Besides, the microstructural characterization of ribbon surface with various Fe/Co ratios in as-received and corroded states was used by scanning electron microscopy. Altering Fe/Co ratios can also improve the anti-corrosion and soft magnetic performances of alloy ribbons. The most positive self-corrosion potential and the smallest corrosion current density are approximately −0.551 V and 2.685 μA/cm² for Fe₂₄Co₄₈Y₃Si₁₀B₁₅ amorphous alloy ribbons. The maximum saturation magnetic flux density is 0.92 T when Fe/Co ratio reaches 1:1. Thus, it can be summarized that FeCoYSiB amorphous alloy ribbons with proper Fe/Co ratio possess the better anti-corrosion property, high microhardness, superior thermal stability and acceptable soft magnetic properties simultaneously, which might broaden possibilities for the development and engineering application of high-performance metal materials.