Crystallization kinetics of Mg61Cu28Gd11 and (Mg61Cu28Gd61)99.5Sb0.5 bulk metallic glasses

The crystallization behavior of Mg61Cu28Gd11 and (Mg61Cu28Gd11)(99.5)Sb-0.5 bulk metallic glasses was studied using differential scanning calorimeter technique under different heating conditions. Under isochronal heating, the onset and peak temperatures of crystallization for these glasses exhibit strong heating-rate dependence. The activation energies for onset and peak crystallization were determined, based on Kissinger plots, to be 77 and 79 kJ/mol, respectively, for Mg61Cu28Gd11 glassy alloy, and 104 and 108 kJ/mol, respectively, for (Mg61Cu28Gd11)(99.5)Sb-0.5 glassy alloy. The isothermal kinetics was modeled by the Johnson-Mehl-Avrami equation. The Avrami exponents suggest that the isothermal crystallizations of the two glassy alloys are both governed by diffusion-controlled growth. On the basis of Arrhenius relation, the activation energies in the isothermal process were calculated to be 88 and 112 kJ/mol, respectively for Mg61Cu28Gd11 and (Mg61Cu28Gd11)(99.5)Sb-0.5 glassy alloys. The superior thermal stability of Sb-additive glassy alloy can be attributed to the strong affinity for Sb/Mg and Sb/Gd, which appears to impose resistance to the formation of Mg2Cu and CusGd phases. (C) 2010 Elsevier B.V. All rights reserved.