Glass-to-crystalline transformation in rapidly quenched Fe78B9Si13 ferromagnetic alloy

Calorimetric studies of the ferromagnetic Curie temperature T_c, and the crystallization kinetics of the metallic glass Fe₇₈B₉Si₁₃ have been performed in an attempt to elucidate the possibility of reversible relaxation processes near T_c and the crystallization mechanisms taking place. From the change of T_c with heating rate and on annealing it appears that ageing irreversibly increases the Curie temperature. Crystallization is thermally activated following an Arrhenius behaviour and proceeds in two stages, the best fit to the experimental data for each stage of crystallization has been obtained by use of a Johnson-Mehl-Avrami-Erofe'ev equation. The effective activation energy and the kinetic exponent are respectively E = (4.7 ± 0.1) eV, n = 2.0 ± 0.2 for the first and E = (4.5 ± 0.1) eV, n = 4.0 ± 0.2 for the second stage of crystallization. From these results it appears that the mechanisms of crystallization are quite different in both stages.