THE CRYSTALLIZATION KINETICS OF FE80SI4B16 METALLIC-GLASS

Differential scanning calorimetry has been used to study the kinetics of crystallization of Fe80Si4B16 metallic ribbon. Continuous heating a nd isothermal measuring techniques were used. Two overlapping exotherm al peaks were always observed. Both processes proceeded by Johnson-Meh l-Avrami crystallization kinetics having temperature- and time-depende nt activation energies. In the first crystallization step E(1)(755 K) = 325 kJ (g atom)(-1) continuously increased to E(1)(794 K) = 487 kJ (g atom)(-1) and the exponent n(1) = 2.5 decreased to 1.5 for extende d degrees of conversion. These observations were interpreted as crysta llization of two types of primary product having quite different kinet ics. In the second crystallization step the exponent n(2) = 4 and the activation energy E(2) having the mean value of 340 kJ (g atom)(-1) d ecreased slightly with increasing temperature. These observations were interpreted as the crystallization of the metastable and stable eutec tic phases.