New sulfur-bearing Bulk Metallic Glasses: Thermophysical and mechanical properties

近年来，发现了一类以硫为主要成分的大块金属玻璃（BMG）成形合金。到目前为止，硫还没有被考虑用于玻璃形成成分的开发。令人惊讶的是，结果表明，含硫bmg可以在广阔的组成空间中产生。此外，还观察到，在现有合金中添加少量硫可以改善从玻璃态加热时的热稳定性，从而通过热塑性成形或增材制造获得更好的可加工性。到目前为止，它仍然是开放的，为什么S稳定亚稳过冷液体(例如在（Ti,Zr)-(Ni,Cu)-S体系中），允许形成大块玻璃样。因此，阐明硫在玻璃形成过程中的作用是很重要的，这是由热力学和动力学贡献决定的。为了理解为什么硫在各种体系中导致玻璃形成能力和热稳定性的关键改善，有必要对其热力学和动力学性质进行广泛的研究。本项目将研究几种含硫合金的热物理性质（如低温粘度、比热容、热力学函数和时间-温度转变图）。特别是，少量添加硫对商业合金(例如，Vitreloy™105 （Zr52.5Cu17.9Ni14.6Al10Ti5), Vitreloy™101 (Cu47Ti34Zr11Ni8)）的影响将被检查并与初始的无硫合金进行比较。本项目的另一个主要课题是研究硫对这些合金力学性能的影响。一般来说，氧、氮、硫等元素通常被认为是金属玻璃中的杂质，它们对玻璃成形能力（GFA）和机械性能有负面影响。因此，我们将研究硫对几种玻璃成形系统中力学性能的影响，并与无硫合金进行比较。最后，将热物理和力学分析结果结合起来，验证了不同作者提出的动态脆性与机械延性之间的相关性。结合高能同步加速器实验，对原子结构与宏观性质之间的关系有了更深入的认识。这些结果将有助于全面了解新型含硫大块玻璃成形合金及其可能的应用领域。

Recently, a new family of bulk metallic glass (BMG) forming alloys containing sulfur as major constituent has been discovered. Up to now, sulfur was not considered for the development of glass forming compositions. Surprisingly, it was shown that sulfur-containing BMGs can be produced in a vast compositional space. Additionally, it was observed that minor additions of sulfur to existing alloys can lead to an improvement of the thermal stability upon heating from the glassy state resulting in a better processability by thermoplastic forming or additive manufacturing. To this point, it remains open, why S stabilizes the metastable undercooled liquid (e.g. in the (Ti,Zr)-(Ni,Cu)-S system), allowing the formation of bulk glassy samples. Thus, it is important to elucidate the role of sulfur for the process of glass formation, which is governed by thermodynamic and kinetic contributions.In order to understand why sulfur leads to a crucial improvement of the glass-forming ability and thermal stability in various systems, extensive research on their thermodynamic and kinetic properties is necessary. In the proposed project, the thermophysical properties (e.g. the low temperature viscosity, the specific heat capacity, the thermodynamic functions and the time-temperature-transformations diagrams) of several sulfur-containing alloys will be investigated. Especially, the effect of minor additions of sulfur to commercially used alloys (e.g. Vitreloy™105 (Zr52.5Cu17.9Ni14.6Al10Ti5), Vitreloy™101 (Cu47Ti34Zr11Ni8)) will be examined and compared to the initial, sulfur-free alloys. The other main topic of this project is the investigation of the influence of sulfur on the mechanical properties of these alloys. In general, elements like oxygen, nitrogen or sulfur are often considered as impurities in metallic glasses, having a negative influence on the glass forming ability (GFA) and the mechanical properties. Therefore, we will study the influence of sulfur on the mechanical properties in several glass forming systems in comparison to sulfur-free alloys.Finally, the results of the thermophysical and mechanical analysis are combined in order to verify a correlation between the kinetic fragility and the mechanical ductility as proposed by different authors. In combination with high energy synchrotron experiments this study will lead to a deeper insight in the relationship between the atomic structure and the macroscopic properties. These results will lead to a comprehensive understanding of the novel, sulfur-bearing bulk glass forming alloys and their possible fields of application.