Crystallization kinetics of Ca65Mg15Zn20 bulk metallic glass

Abstract

The crystallization behavior of Ca65Mg15Zn20 bulk metallic glass was studied by means of differential scanning calorimetry. Under continuous heating, the glass transition and crystallization exhibit strong heating rate dependence. The activation energies for glass transition, onset and peak crystallizations were determined, based on the Kissinger relation, to be 148±4, 123.5±2 and 116±7kJ/mol, respectively. In the case of isothermal annealing, the crystallization kinetics was modeled by the Johnson–Mehl–Avrami equation. The Avrami exponents ranged from 2.08 to 2.67 indicating a diffusion-controlled three-dimensional growth, and the local Avrami exponents and activation energies were also calculated. Besides, the crystallization product after isothermal annealing was detected to be CaMg2 by X-ray diffraction, and the particle size was evaluated to be about 5nm. The reasons for the formation and the crystal size of the CaMg2 phase were discussed.