| 1. |
- Goetz, Inga K., 1992-, et al.
(author)
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Convective Flow Redistribution of Oxygen by Laser Melting of a Zr-Based Amorphous Alloy
- 2023
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In: Materials. - : MDPI. - 1996-1944. ; 16:11
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Journal article (peer-reviewed)abstract
- Oxygen impurities play a crucial role in the glass-forming ability and crystallisation behaviour of metallic glasses. In the present work, single laser tracks were produced on Zr59.3-xCu28.8 Al10.4Nb1.5Ox substrates (x = 0.3, 1.3) to study the redistribution of oxygen in the melt pool under laser melting, which provides the basis for laser powder bed fusion additive manufacturing. Since such substrates are commercially not available, they were fabricated by arc melting and splat quenching. X-ray diffraction revealed that the substrate with 0.3 at.% oxygen was X-ray amorphous, while the substrate with 1.3 at.% oxygen was partially crystalline. Hence, it is evident that the oxygen content affects the crystallisation kinetics. Subsequently, single laser tracks were produced on the surface of these substrates, and the melt pools attained from the laser processing were characterised by atom probe tomography and transmission electron microscopy. Surface oxidation and subsequent convective flow redistribution of oxygen by laser melting were identified as causes of the presence of CuOx and crystalline ZrO nanoparticles in the melt pool. Bands of ZrO likely originate from surface oxides that were moved deeper into the melt pool by convective flow. The findings presented here highlight the influence of oxygen redistribution from the surface into the melt pool during laser processing.
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| 2. |
- Tidefelt, Mattias, et al.
(author)
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In Situ Mapping of Phase Evolutions in Rapidly Heated Zr-Based Bulk Metallic Glass with Oxygen Impurities
- 2024
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In: Advanced Science. - : John Wiley & Sons. - 2198-3844. ; 11:16
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Journal article (peer-reviewed)abstract
- Metallic glasses exhibit unique mechanical properties. For metallic glass composites (MGC), composed of dispersed nanocrystalline phases in an amorphous matrix, these properties can be enhanced or deteriorated depending on the volume fraction and size distribution of the crystalline phases. Understanding the evolution of crystalline phases during devitrification of bulk metallic glasses upon heating is key to realizing the production of these composites. Here, results are presented from a combination of in situ small- and wide-angle X-ray scattering (SAXS and WAXS) measurements during heating of Zr-based metallic glass samples at rates ranging from 102 to 104 Ks-1 with a time resolution of 4ms. By combining a detailed analysis of scattering experiments with numerical simulations, for the first time, it is shown how the amount of oxygen impurities in the samples influences the early stages of devitrification and changes the dominant nucleation mechanism from homogeneous to heterogeneous. During melting, the oxygen rich phase becomes the dominant crystalline phase whereas the main phases dissolve. The approach used in this study is well suited for investigation of rapid phase evolution during devitrification, which is important for the development of MGC. Oxygen impurities impact on phase-transformations during rapid heating of Zr-based metallic glass Zr59.3Cu28.8Al10.4Nb1.5 is thoroughly investigated using a multi-technique approach. During devitrification, the extracted phase evolutions reveal that the phase fraction hierarchy correlates with the oxygen impurity concentration. Numerical simulations with a heterogeneous nucleation mode capture the experimental observations. During melting, the oxygen-rich phase becomes the dominant phase. image
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| 3. |
- Weiszflog, Matthias, et al.
(author)
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Transforming laboratory experiments for digital teaching : remote access laboratories in thermodynamics
- 2022
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In: European journal of physics. - : IOP Publishing. - 0143-0807 .- 1361-6404. ; 43:1
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Journal article (peer-reviewed)abstract
- Laboratories in an undergraduate physics course were adapted to remote learning while conserving a high degree of student autonomy regarding the experimental work. The commencement of the COVID-19 pandemic in 2020 and the resulting restrictions for large groups enforced the immediate development and implementation of new teaching concepts. This article describes laboratories, which have been redesigned in order to give the students the possibility to remotely steer and control the experiments by instructing their teachers, who were on site in the laboratory. This interactive approach allowed for a high degree of autonomy and freedom in the experimental design. The assessment of the laboratories, oral presentations by the students, was carried out in a similar format as in previous years, but remotely. The presentations indicated that the students reached a comparable level of understanding of the underlying physics concepts as in years with on-site laboratories. The experiences gathered with this concept can be beneficial beyond the described one-time implementation and allow adaptation for other scenarios of remote courses.
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