Time-Scaling Properties and Crystallization Kinetics of Amorphous Alloys

Abstract

We have investigated the time-scaling properties of the isothermal crystallization kinetics for amorphous Co 75 B 25 , Fe 8O B 2O , Fe 40 Ni 40 B 20 , Fe 81 B 17 Si 2 and Fe 60 Ni 20 B 10 Si 10 alloys by differential scanning calorimetry. All the alloys exhibit a single crystallization stage. The time scale was defined as the time when the crystallization has reached half completion. All the time-scaled crystallization curves of each alloy fall onto a single muster curve of the Johnson-Mehl-Avrami form in each case. The Avrami exponent indicates that the crystallization process of the Fe 60 Ni 20 B 10 Si 20 is governed by interface-controlled growth with a constant nucleation rate, whereas those of the other alloys are by interface-controlled growth of a fixed number of nuclei. The Williams-Landel-Ferry equation based on a free-volume consideration gives a universal function of time-scaling parameter as a function of temperature for all the alloys. This suggests that we have to take into account the relaxation occurring in the amorphous phase outside the crystallite in the crystallization process.