Composition design and crystallization behavior of Zr–Cu–Ni–Al bulk metallic glasses

Abstract

The Zr–Cu–Ni–Al system was explored in this study, and seven new compositions of Zr-based bulk metallic glasses (BMGs) were designed by combining different proportions of binary eutectic phases Zr₃₈Cu₆₂, Zr₇₆Ni₂₄ and Zr₅₁Al₄₉, and rod-like shape samples were prepared with different diameters using the copper mold casting method. Modifying the proportion coefficient of these eutectic units, the width of the supercooled liquid region was increased from 79 to 95 K, and the thermal stability of the prepared metallic glass was improved. Differential scanning calorimetry was used to investigate the non-isothermal and isothermal crystallization behavior of the prepared samples. Noticeably, there was a small low-temperature exothermic peak before the glass transition temperature T_g in the non-isothermal crystallization process, which was related to the structural relaxation. The crystallization transition activation energy fitted by the Kissinger equation had the same variation trend as that obtained by the Arrhenius equation. Among the four metallic glasses studied, the glassy phase of Zr_55·5Cu_23·25Ni₉Al_12.25 was more stable, showing higher glass transition activation energy and longer incubation time. In addition, the isothermal crystallization processes of four metallic glasses were studied according to the Johnson-Mehl-Avrami (JMA) model. The calculated average Avrami exponents were >2.5, indicating that the nucleation rate increased during the isothermal crystallization process.