Neue schwefelhaltige Metallische Massivgläser: Thermophysikalische und mechanische Eigenschaften
Zusammenfassung der Projektergebnisse
High Sulfur additions All in all, the high kinetic fragility in combination with the high driving force for crystallization strongly limit the GFA. Glass formation is suggested to take place because of a high interfacial energy between the liquid and the crystalline solid. The interfacial energy is also suggested to determine the location of the GFR in this system, which is a function of S-content. This is concluded since estimations of the kinetic fragility indicate an unchanged fragility index D* with compositional changes. Estimations of the driving force for crystallization by the entropy of fusion indicate even a decreasing ΔGl-x at lower S-contents (below 26 at%). Thus, these two parameters point towards a higher GFA for lower S contents, but the GFA diminishes, which is assumed to be caused by a change of either interfacial energy or rather the primary phase. Medium Sulfur additions In case of the kinetically strong Ti/Zr-based bulk glass forming alloys, the sluggish kinetics above and below the liquidus temperature are responsible for the frustration of the crystallization process. The S-additions cause a drastic drop of the surface tension in comparison to pure Ti/Zr-alloys, which is suggested to improve the molding accuracy and the achievable surface quality in casting processes. Regarding their properties, especially the Ti-based alloys are of the greatest interest for industrial applications, as 3 mm amorphous rods of Ti40Zr35Cu17S8 can be produced from industrial grade raw materials, drastically decreasing material costs. Furthermore, these alloys possess excellent mechanical properties like an outstanding strengthto-density ratio, as well as a high hardness in the as-cast state. The low content of late transition metals (Cu, Ni) together with the high amounts of Ti result in an excellent corrosion behavior in chloride solutions, which has so far not been achieved with any other Ti- or Zr-based BMGs. Parts produced from this alloy are able to outperform crystalline Ti-alloys like Ti6Al4V. Low sulfur additions to industrially relevant alloys In conclusion minor additions of S allow for distinct modifications of an alloy without completely changing the characteristics of the alloy family. Properties like the density, the elastic modulus, or the hardness remain mostly unchanged. However, especially the properties connected to the kinetics of the system, e.g. the length of the SCL region, the kinetic fragility, as well as the crystallization behavior, and hence GFA, can be changed drastically by minor additions of an element. Regarding the thermoplastic formability of the alloys, the thermal stability and the viscosity are the decisive factors, both of which are largely influenced by minor additions. Therefore, the formability of BMGs is a property that is highly sensitive to modifications by minor additions. This can impressively be confirmed by the thermoplastic deformation experiments on the Vit101 and Vit105 alloys and their modifications. Although, most modifications of the alloys result in a tradeoff between different properties: An increased thermoplastic formability can go along with a reduced GFA, or an embrittlement. Therefore, minor additions of S should not necessarily be seen as a universal tool to improve the properties of BMGs, but rather as a simple way to fine-tune a wide variety of properties to the desired use case. Overall parallels of sulfur-bearing compositions and potential outlook It is evident that S has not a universal role for the glass formation process and the resulting properties such as the kinetic, thermodynamic or mechanical properties. Still some similarities between the Pd- and the Ti-/Zr-based systems are observed. It is conspicuous that all alloys with a high Ni-content such as Pd31Ni42S27, Ti60Zr15Ni17S8 and Ni58Nb39S3 show a very brittle mechanical behavior. This might originate from the bonding character between Ni and S. Substitution of Ni by Cu in the Ti60Zr15Ni17S8 system led to a drastic improvement of the ductility, which is suggested to be caused by the reduction of the number of the Ni-S bonds. However, these are only speculations and for a more concrete proposition a detailed investigation of the types of bonds is necessary. The equilibrium liquid of all S-alloys shows drastic drop of the surface tension and high wet-ability on water-cooled Cu, which is suggested to originated from the high surface activity of S. Both aspects and especially the nature of the atomic bonds within the liquid and glassy state are open questions that need to be solved in the future.
Projektbezogene Publikationen (Auswahl)
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Development, Characterization and Processing of a novel Family of Bulk Metallic Glasses: Sulfur-containing Bulk Metallic Glasses. Dissertation, Saarland University
Kuball, A.
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Thermophysical and Structural Investigations of a CuTi- and a Zrbased Bulk Metallic Glass, the Influence of Minor Additions, and the Relation to Thermoplastic Forming. Saarland University, Dissertation. Dissertation, Saarland University
Bochtler, B.
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Bulk metallic glass formation in the (Ti,Zr)–(Ni,Cu)–S system. Journal of Physics: Condensed Matter, 32(26), 264003.
Gross, Oliver; Ruschel, Lucas; Kuball, Alexander; Bochtler, Benedikt; Adam, Bastian & Busch, Ralf
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Changes in the crystallization sequence upon sulfur addition in the Zr52.5Cu17.9Ni14.6Al10Ti5 bulk metallic glass-forming liquid revealed by in situ high-energy x-ray diffraction. Physical Review Materials, 5(10).
Bochtler, Benedikt; Mariño-Salguero, Jessica Marcela; Kuball, Alexander; Gross, Oliver; Yang, Fan; Meyer, Andreas; Buslaps, Thomas; Rütt, Uta & Busch, Ralf
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Effect of sulfur on the glass-forming ability, phase transformation, and thermal stability of Cu-Zr-Al bulk metallic glass. Acta Materialia, 212, 116923.
Jiang, Hao-Ran; Hu, Jing-Yi; Neuber, Nico; Bochtler, Benedikt; Adam, Bastian; Riegler, Sascha S.; Frey, Maximilian; Ruschel, Lucas; Lu, Wen-Fei; Feng, Ai-Han; Busch, Ralf & Shen, Jun
