Kinetic and structural investigations of deeply undercooled Zr-based bulk metallic glass forming liquids

点击翻译按钮获取中文摘要

In recent years, studies of various multicomponent glass forming liquids have revealed a discrepancy between fragile liquid behavior in the equilibrium melt and strong liquid behavior in the glassy state. This has been attributed to a polymorphic liquid-liquid (L-L) transition between two different liquid phases, each exhibiting distinct thermodynamic and kinetic signatures. Using a Couette rheometer, Busch and coworkers observed a direct Strong-Fragile transition for Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 (Vit1). To expand upon this work, the groups at the Chair of Metallic Materials in Saarbrücken and the Institute for Material Physics in Space in Köln have jointly investigated possible S-F transitions for select Zr-based metallic glass forming liquids. This project focused on obtaining unambiguous viscosity, density, and heat capacity data in the equilibrium melt and deeply undercooled liquid by comparing both conventional experimental techniques as well as containerless techniques, the results of which are summarized in this report. All of the alloys consistently showed the discrepancy in high and low temperature fragilities. However, unlike Vit1, direct observation of the S-F transition was obscured behind the onset of crystallization for all of the compositions. Preliminary works have been extended to calorimetric and synchrotron diffraction investigations of Vit1 and Zr58.5Cu15.6Ni12.8Al10.3Nb2.8 (Vit106a) liquids. Such in-situ studies with levitation allow distinguishing between crystallization and the L-L transition as well as monitoring liquid structure factor S(Q) from equilibrium melt down to glass transition. For both alloys systems thermodynamic and structural anomalies associated with the S-F transition have been revealed in the deeply undercooled liquid. The goal of the proposed project is thus to gain insight into the structural and thermodynamic changes associated with the S-F transition by employing in-situ X-ray diffraction measurements. Combined with the previous results, this will enable a comprehensive description of the thermodynamic, kinetic, and structural aspects of the S-F transition.