Calorimetric study of non-isothermal crystallization kinetics of Zr 60Cu 20Al 10Ni 10 bulk metallic glass

Abstract

The non-isothermal differential scanning calorimetric techniques were used to evaluate the thermal stability and crystallization kinetics of Zr 60Cu 20Al 10Ni 10 bulk metallic glass. Various models were used to analyze the non-isothermal DSC at the heating rates ( ϕ) ranging from 1 to 80 K/min. The Kissinger equation, Ozawa equation, Augis-Bennett equation, Lasocka equation, and Vogel–Fulcher–Tammann non-linear equation were employed to describe the relationship between the crystallization peak temperatures and the heating rates. The overall crystallization activation energies of the metallic glass were estimated using the Kissinger, Ozawa and Augis–Bennett methods, respectively. The local activation energies at various volume fraction of crystalline phases were obtained by general Ozawa's isoconversional method. The crystallization kinetics was specified by a function reflecting crystallization mechanism. It has been found that a critical heating rate exists at around 20 K/min, beyond which the shapes of the DSC curves and the various relationships are varied. The crystallization process of the metallic glass can be divided into two groups, i.e. a slow heating rates region with ϕ = 1–20 K/min, and a rapid heating rates region with ϕ = 30–80 K/min. The overall crystallization activation energy for the slow heating rates regions is much larger than that for the rapid heating rates region. The crystallization activation energy derived from the Kissinger's peak temperatures is 326.4 ± 11.3 kJ/mol for the slow heating rates region, and 202.2 ± 26.6 kJ/mol for rapid heating rates region, respectively. The crystallization mechanisms were discussed with Johnson–Mehl–Avrami (JMA) and normal grain growth (NGG) mode. The crystallization mechanisms are different for the two heating rates regions. A transition point was found at the NGG-controlled crystallization stage for the higher heating rates, while it was absent for the slower heating rates.