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

近年来，对各种多组分玻璃形成液的研究揭示了平衡熔体中的脆弱液体行为与玻璃态中的强液体行为之间的差异。这归因于两种不同液相之间的多晶液-液（L-L）转变，每种液相都表现出不同的热力学和动力学特征。使用Couette流变仪，Busch和同事观察到Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 （Vit1）的直接强-脆性转变。为了扩展这项工作，saarbr<e:1> cken金属材料主席和Köln空间材料物理研究所的小组共同研究了选择zr基金属玻璃形成液体的可能S-F转变。本项目通过比较常规实验技术和无容器实验技术，重点获得平衡熔体和深度过冷液体的明确粘度、密度和热容量数据，本报告对结果进行了总结。所有合金均表现出高低温脆性的差异。然而，与Vit1不同的是，S-F跃迁的直接观测被掩盖在所有成分结晶开始的背后。初步工作已扩展到Vit1和Zr58.5Cu15.6Ni12.8Al10.3Nb2.8 （Vit106a）液体的量热和同步加速器衍射研究。这种悬浮的原位研究可以区分结晶和L-L转变，以及监测从平衡熔融到玻璃化转变的液体结构因子S(Q)。对于这两种合金系统，在深度过冷的液体中都揭示了与S-F转变相关的热力学和结构异常。因此，拟议项目的目标是通过采用原位x射线衍射测量来深入了解与S-F转变相关的结构和热力学变化。结合之前的结果，这将能够全面描述S-F转变的热力学、动力学和结构方面。

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.