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

点击翻译按钮获取中文摘要

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.