Fig. 1 Diagram of the wedge-shaped casting apparatus consisting of a melting and a temperature measurement. The thermocouples are embedded on the axis of the copper mold cavity at 3, 10 and 20 mm away from the tip of the wedge

Fig. 2 Measured (dotted lines) and calculated (solid lines) cooling temperature curves during wedge-casting. The distances indicated in the legend are measured along the z-axis from the tip of the wedge: 3 mm (black), 10 mm (red), and 20 mm (blue). To reflect the temperature change in the initial stage of solidification, the inset shows a magnified view of the first 0.4 s

Fig. 3 Thermogram of the Fe-based glass-forming alloy ingot after 0.0259 s of cooling. The imposed lines indicate the range of possible isothermal contours during cooling based on the appearance of the glass-crystalline transition region. The cooling rates corresponding to the isothermal contours line are shown in the thermogram. The isothermal contours at the tip of the wedge specimen are enlarged and placed at the bottom right

Fig. 4 Microstructural features on the cross section a and corresponding X-ray spectra at different locations b of the wedge-shaped ingot. The microstructural features of the ingot are congruent to the contrast visible in the thermograms (Fig. 3), and a transition from amorphous to polycrystalline is evident. The X-ray spectra refer to the regions (position 1, 3 mm away from the tip of the wedge; position 2, 10 mm away from the tip of the wedge; position 3, 20 mm away from the tip of the wedge) are described

Fig. 5 Microstructure images and corresponding EDS mapping results of the wedge-shaped ingot observed at different positions: SEM image a at the position of 10 mm away from the tip of the ingot and the corresponding EDS mapping results b-e in the red box; SEM image f at the position of 20 mm away from the tip of the ingot and the corresponding EDS mapping results g-j in the yellow box

Fig. 6 a Isothermal DSC traces of Fe-based ribbons annealed at various temperatures between Tg and Tx, Tanneal = 798 K, 803 K, 808 K, 813 K, 823 K and 828 K, respectively. b Fit of the crystallization onset time by rearranging Eq. (7) to get B (K) and T0 (K) for a given Γ. c TTT curves for a given set of C (KJ2 /m6)

Fig. 7 Schematic TTT diagrams on account of the calculated Rc in Table 1 with four phases in Fe-based metallic glass: α-Fe, {Fe, Ni}, Fe2P and M23B6

Fig. 8 a DSC measurement of the Fe-based amorphous alloy ribbon at a heating rate of 20 K/min. Three distinct crystallization events are apparent and the onset crystallization temperature Tx are 835 K, 898 K and 995 K, respectively. The total crystallization heat is determined to be − 260.8 J/g. b XRD patterns of Fe-based alloy ribbons annealed at the temperature of 773 K, 873 K, 923 K and 1023 K and the time of 2 h

Fig. 9 Summary of cooling curves and TTT diagrams. Region A (gray) is the experimental and calculated isothermal TTT curve of the Fe-based alloy; Region B (blue) is the calculated TTT curves of the four crystal phases; Region C (yellow) is the cooling curves measured at different locations during solidification. The cooling curve at 3 mm leading to amorphous phase during casting does not intersect the TTT curves, but the cooling curves at 10 mm and 20 mm cut the TTT diagrams and in good agreement with the XRD data; Region D (orange) is the phase precipitation sequence upon heating at a rate of 20 K/min