Different Methods for Calculation of Activation Energies During Non-Isothermal Annealing of Mg72Zn27Pt1 and Mg72Zn27Cu1 Metallic Glasses.

Mg₇₂Zn₂₇Pt₁ and Mg₇₂Zn₂₇Cu₁ metallic glasses were produced using a melt-spinner. Their crystallization kinetics were investigated during annealing with five heating rates using DSC. Amorphous Mg₇₂Zn₂₇Pt₁ crystallized in the form of one and Mg₇₂Zn₂₇Cu₁ crystallized in the form of two exothermic crystallization peaks. It was noticed that the glass transition, the onset crystallization and the crystallization peak temperatures were strongly heating-rate-dependent. The addition of Pt and Cu increased the stability compared to that of binary Mg-Zn glass, and especially so with Pt, due to its higher melting point and different atom size to those of Mg and Zn. The activation energies were calculated using six model-free methods: the Kissinger, Ozawa-Flynn-Wall, Boswell, Tang, Augis-Bennett and Gao-Wang methods. The Augis-Bennett and Gao-Wang methods allow for the calculation of only the activation energy at the crystallization peak but they are the only ones that consider Tx or dx/dT. For Mg₇₂Zn₂₇Pt₁, the calculated values fluctuate in the ranges 114.60-117.99 kJ/mol, 102.46-105.98 kJ/mol and 71.16-98.62 kJ/mol for Eg, Ex and Ep, respectively, whereas, for Mg₇₂Zn₂₇Cu₁, the calculated values are in the ranges of 98.51-101.77 kJ/mol, 95.15-98.51 kJ/mol and 55.15-93.34 kJ/mol for Eg, Ex and Ep, respectively. Both alloys are meta-stable in the amorphous state and crystallization occurs spontaneously. The Kissinger, Ozawa-Flynn-Wall, Tang and Boswell methods give similar values for the activation energy. The Gao-Wang method significantly underestimates values compared to other methods. The Augis-Bennett method shows much lower values for the local activation energy. Considering the ease of their formulas, best convergence and widespread use in the literature, the Kissinger and Ozawa-Flynn-Wall methods will work very well for any comparison.