Time-scaling properties and crystallization kinetics of amorphous alloys

Abstract

We have investigated the time-scaling properties of the isothermal crystallization kinetics for amorphous Co75B25, Fe80B20, Fe40Ni40B20, Fe81B17Si2 and Fe60Ni20B10Si10 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 Fe60Ni20B10Si10 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.