Non-isothermal Crystallization Kinetics and Isothermal Crystallization Kinetics in Supercooled Liquid Region of Cu-Zr-Al-Y Bulk Metallic Glass

The crystallization kinetics of Cu43Zr48Al9 and (Cu43Zr48Al9)(98)Y-2 bulk metallic glasses in non-isothermal and isothermal conditions was studied by differential scanning calorimetry. In the non-isothermal and isothermal modes, the average activation energy of (Cu43Zr48Al9)(98)Y-2 is larger than that of Cu43Zr48Al9, meaning the higher stability against crystallization of (Cu43Zr48Al9)(98)Y-2. In addition, the average activation energies for Cu43Zr48Al9 and (Cu43Zr48Al9)(98)Y-2 calculated using Arrhenius equation in isothermal mode are larger than the values calculated by Kissinger-Akahira-Sunose method in non-isothermal mode, indicating that the energy barrier is higher in isothermal mode. The Johnson-Mehl-Avrami model was used to analyze the crystallization kinetics in the non-isothermal and isothermal modes. The Avrami exponent n for Cu43Zr48Al9 is above 2.5, indicating that the crystallization is mainly determined by a diffusion-controlled three-dimensional growth with an increasing nucleation rate, while the Avrami exponent n for (Cu43Zr48Al9)(98)Y-2 is in the range of 1.5-2.5 in the non-isothermal mode, implying that the crystallization is mainly governed by diffusion-controlled three-dimensional growth with decreasing nucleation rate. Finally, the Avrami exponents n for Cu43Zr48Al9 and (Cu43Zr48Al9)(98)Y-2 are different in the non-isothermal and isothermal conditions, which imply different nucleation and growth behaviors during the crystallization processes.