Crystallization behavior of C-containing FINEMET amorphous alloy melt-spun ribbon

The crystallization kinetics of amorphous Fe68.5Si13.5B9Cu1Nb3C5 (at. pct) melt-spun ribbons were studied by the DSC method in the mode of continuous heating. The apparent activation energy E-p1 and E-p2 (373.07+/-7.92 and 518.75+/-21.35 kJ/mol, respectively) derived from the Kissinger plots were calculated by the peak temperatures TO, T-p2, which display a strong dependence on the heating rates. The crystallization behavior during isothermal annealing at 823 K for 1, 5, 10 h and 973 K for 5 h were investigated using XRD and TEM. The results show that crystallization behavior becomes completely different from that of FINEMET. It is not bcc alpha-Fe (Si) but metastable fcc gamma-Fe (Si) that participates in the first crystallization step combining the appearance of Fe23B6 and Nb2B. Therefore, the addition of C promotes the combination of Fe and B. Fe3.5B is participated in the second step together with the disappearing of Fe23B6, which indicates that transition Fe23B6-->Fe3.5B+Fe2B presumably happens. gamma-Fe (Si) with peculiar stability cannot transform into nano-sized a-Fe (Si) crystals until the amorphous ribbons were annealed for 5 h at 973 K.