Composition analysis at the nm-scale, marking the onset of clustering in bulk metallic glasses, can aid the understanding and further optimization of additive manufacturing processes. By atom probe tomography, it is challenging to differentiate nm-scale segregations from random fluctuations. This ambiguity is due to the limited spatial resolution and detection efficiency. Cu and Zr were selected as model systems since the spatial distributions of the isotopes therein constitute ideal solid solutions, as the mixing enthalpy is, by definition, zero. Close agreement is observed between the simulated and measured spatial distributions of the isotopes. Having established the signature of a random distribution of atoms, the elemental distribution in amorphous Zr59.3Cu28.8Al10.4Nb1.5 samples fabricated by laser powder bed fusion is analyzed. By comparison with the length scales of spatial isotope distributions, the probed volume of the bulk metallic glass shows a random distribution of all constitutional elements, and no evidence for clustering is observed. However, heat-treated metallic glass samples clearly exhibit elemental segregation which increases in size with annealing time. Segregations in Zr59.3Cu28.8Al10.4Nb1.5 > 1 nm can be observed and separated from random fluctuations, while accurate determination of segregations < 1 nm in size are limited by spatial resolution and detection efficiency.

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.

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.