Scientific Events

While the general principles underlying the plastic response of metals are mostly understood—especially for the crystalline state—advanced tailoring of their properties and the development of novel, high-performance materials requires detailed insights into the mechanisms at the atomic scale. This talk will discuss how computer models and simulations can be the tools of choice to discover such mechanisms in the context of our work on amorphous metals and wear. I will first introduce some concepts of molecular dynamics computer simulations and how we used them to investigate the plastic deformation of metallic crystal/glass composites, where localized and collective shear transformations govern the macroscopic behavior. In particular, I will address the questions of when and how precipitates can enhance the mechanical properties of metallic glasses and what the difference between a nanocomposite and a nanocrystal is. In the second part, I will discuss our current work on wear of materials and what to do when the time and length scale limitations of molecular dynamics become a problem. When surfaces in contact slide relative to each other, they are in fact only in contact in some small areas due to their roughness. At this length scale, we employ molecular dynamics with different model materials in order to elucidate how detachment of matter occurs in the form of individual particles, which in the end comes down to the details of nanoscale plasticity and fracture processes. In order to gain insights on relevant figures of merit for applications, though, we have to collect statistics of wear particle formation at the meso to macroscale, using continuum methods. Since some of this work is in its early stages, I will finish the talk with a preview of promising future research directions and methods, such as taking the microstructure evolution of the material into account. [more]

Analytical electron microscopy is applied to study elementary processes which govern micro- and nanostructural evolution and their effect on structural and functional properties in two-phase material systems. Modern computational alloy design for application relevant blade materials operating at high temperatures require reliable diffusion data, which consider the realistic superalloy condition. A new method will be presented to study diffusion kinetics in compositionally complex superalloys using intrinsic nano-diffusion-couples that are exposed to in situ and ex situ annealing experiments. Magnetic two-phase Heusler compounds are fascinating because they enable to study the influence of misfit induced strain gradients at interfaces on magnetic texture formation. Micro-engineering of misfit induced strains into a functional magnetic composite represents a novel approach which may well pave the way towards a new era of exploiting flexomagnetism, an area which has yet to be explored experimentally. [more]

Titanium is the fourth most abundant engineering material in the Earth’s crust. Although it has many beneficial properties, the cost of extraction remains a challenge and over 90% of high grade titanium is derived from the expensive and time-consuming Kroll Process. Electro-refining methods show promise but present their own special challenges. We present an overview and update of a novel molten salt process to extract and refine low-grade ores to produce high-grade powder titanium. Titanium oxycarbide produced by carbothermic reduction is electro-refined in a molten eutectic bath of NaCl:KCl salt. Anodic dissolution causes the Ti product to be plated out in the form of a dendritic product which collects on the cathode while impurities are retained in the anode. A gentle introduction to the process will be given and recent studies to apply the method to include the effect of using ilmenite and ilmenite/rutile blends as a feedstock, as well as the applicability of the process to other metals, specifically niobium (Nb) and vanadium-baring minerals presented. [more]

Microscopy, by definition, is the science of using a microscope to observe objects that are unseen by the naked eye. However, astronomical objects such as planets, moons and comets or asteroids are easily identifiable in the night sky, yet scientists are increasingly relying on microscopic methods to investigate their composition, structure, and determine their origins. Whether this is via extra-terrestrial exploration with satellites, landers or rovers, or by studying returned astromaterials in the laboratory itself, the use of microscopy within the diverse field of planetary science is quickly becoming the norm. Correlating multiple microscopic and spectroscopic methods within the scanning electron microscope (SEM) when studying meteorites allows us to extend the spectrum from nano or micro-scale imaging at one end, all the way up to the astronomical scale at the other. For example, the Mars Science Laboratory (MSL) rover, Curiosity, landed in Gale Crater; a region that had been heavily investigated using satellite data from previous mission Mars Odyssey. Using similar infrared microscopic methods in the laboratory, we can distinguish the same compositions within Martian meteorites as those directly observed on the Martian surface.Recent studies (e.g. Stephen et al. 2014; King et al. 2018) have combined traditional SEM imaging and analysis (energy-dispersive spectroscopy - EDS, electron-backscatter diffraction – EBSD, wavelength-dispersive spectroscopy – WDS) with micro Fourier transform infrared (μFT-IR) to inform the varied geological histories of meteorite parent bodies, including aqueous alteration on both asteroids and planets. Further studies combine SEM & TEM imaging with other X-ray techniques at varying scales, i.e. X-ray microscopy (XRM) or X-ray tomography (XRT), to help classify new meteorites and examine potential parent bodies throughout the Solar System (MacArthur et al. 2019).Non-destructive, microscopic methods allow for detailed investigation through multiple volumes that would otherwise be inaccessible without damaging the specimens themselves; a crucial consideration when working with limited material from an extra-terrestrial source. Correlating microscopy techniques across instruments, scales and disciplines is perhaps one of the best approaches to studying these astromaterials, and fully unravelling their geological history, as well as their journey to Earth.References:King et al. (2018) Investigating the history of volatiles in the solar system using synchrotron infrared micro-spectroscopy' Infrared Physics and Technology 94, 244-249.MacArthur et al. (2019) Mineralogical constraints on the thermal history of Martian regolith breccia Northwest Africa 8114, Geochimica et Cosmochimica Acta 246, 267-298.Stephen et al. (2014) Mid-IR mapping of Martian meteorites with 8-micron spatial resolution, Meteoritics and Planetary Science, pp A381. [more]

In this talk, the work within the Biomechanics Research Team at the Laboratory for Mechanics of Materials and Nanostructures of Empa on micromechanics of bone will be presented. Fundamental research on the failure mechanisms of bone on the microscale as a function of loading mode will be discussed. Nanostructural characterization is combined with micromechanical experimentation and mechanical modeling to allow identifying structure-property relationships in this complex nanocomposite. Recent technical developments allowing experiments with well defined boundary and environmental conditions in a broad strain rate range are employed to investigate the effect of water on the strain rate dependence of bone on the microscale. Furthermore, direct clinical applications of this fundamental research for assessing bone quality of patients in clinical studies will be discussed. [more]

In 1950, Bowden and Tabor pointed out that in metallic tribological contacts the majority of the dissipated energy is spend to change the contacting materials’ microstructures. This – in part – explains why most metals show a highly dynamic subsurface microstructure under the shear load imposed by a sliding contact. In order to understand these processes, the elementary mechanisms accommodating the shear strain and acting in the material need to be revealed and understood. In this presentation, three examples of research avenues following this hypothesis will be given. During the very early stages of sliding, dislocations show an interesting self-organization phenomenon. How these structures interfere with twin boundaries and what might be learned about the dislocation motion under the slider will be the first part of the talk. Second, we will address how the high entropy alloy (HEA) CoCrFeMnNi reacts to a tribological load and whether there is evidence for mechanisms specific to HEAs. Third, we will focus our attention at tribo-chemically activated oxidation process studied for high-purity copper. [more]

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