Kinetics of crystallization process for Pd-based bulk metallic glasses

Abstract

The crystallization behavior of Pd 79Cu 6Si 10P 5 and Pd 79Cu 4Au 2Si 10P 5 bulk metallic alloys was studied using differential scanning calorimeter (DSC) under different heating conditions. Under isochronal heating, the onset temperatures of the glass transition and crystallization for these glasses exhibited strong heating-rate dependence. The activation energies for the glass transition and crystallization were determined, based on the Kissinger plots, to be 540 and 452 kJ/mol, respectively, for Pd 79Cu 6Si 10P 5 glassy alloy, and 640 and 318 kJ/mol, respectively, for Pd 79Cu 4Au 2Si 10P 5 glassy alloy. The isothermal kinetics was modeled by the Johnson–Mehl–Avrami equation. For the Pd 79Cu 6Si 10P 5 glassy alloy the Avrami exponent was mostly in the range from 2.23 to 2.52, which indicated a decreasing nucleation rate and a diffusion-controlled three-dimensional growth. For the Pd 79Cu 4Au 2Si 10P 5 glassy alloy the Avrami exponent was in the range between 2.42 and 2.76, which indicated an increasing nucleation rate and a diffusion-controlled three-dimensional growth.