Calorimetric study of the crystallization kinetics ofCu47Ti33Zr11Ni8Si1metallic glass

Abstract

The isochronal and isothermal activation energies for the primary crystallization process of ${\mathrm{Cu}}_{47}{\mathrm{Ti}}_{33}{\mathrm{Zr}}_{11}{\mathrm{Ni}}_{8}{\mathrm{Si}}_{1}$ metallic glass powders subjected to varying thermal treatments have been evaluated by differential scanning calorimetry and determined using the Kissinger approach and the Johnson-Mehl-Avrami (JMA) analysis, respectively. The values of the differential Avrami exponent are also determined from the isothermal data. Assuming diffusion-controlled growth, it is shown that thermal treatment of the samples in the supercooled liquid region considerably influences the behavior of the nucleation rate during the crystallization process. Microstructural investigations indicate that the thermal treatment is accompanied by precipitation of fine nanocrystals in an amorphous matrix. The values for the activation energies determined by both the Kissinger approach and the JMA analysis are similar for the as-prepared powder, but a significant difference is found for the thermally treated powders. This discrepancy is explained on the basis of the fundamental assumptions made in the models. It will be shown that the Kissinger method fails if the differential Avrami exponent changes significantly during the transformation process.