An Analysis of Crystallization Process in Amorphous Alloys Using Time-Scaling Factor

Abstract

We have investigated the time-scaling properties of the isothermal crystallization process for Cu 66 Ti 34 and Zr 65 Cu 35 amorphous alloys by differential scanning calorimetry. Local atomic structures have also been studied by extended X-ray absorption fine structure (EXAFS) measurements. The results are discussed in comparison with the previous results obtained for metal-metalloid amorphous alloys. The timescaling factor is defined as the time when the crystallization has reached half completion. By rescaling the time axis for each annealing temperatures, the crystallization curves measured at various temperatures for each alloy can be superimposed on a single curve in each case. The Williams-Landel-Ferry formula based on a free-volume consideration gives a universal function for the temperature dependence of the timescaling factor for all the alloys. This suggests that we have to take into account the relaxation process occurring in the amorphous phase during the crystallization. The WLF analysis reveals that there exists a significant difference in the temperature dependence of the scaling factor between the metal-metal and metal-metalloid amorphous alloys. From the EXAFS study, such difference is considered to be due to the local structural differences between those two types of amorphous alloys.