Research

Research

On this page you can find information about ongoing research in the group.

Alexander Müllner, PhD student

Experimental setup for small angle and wide angle X-ray measurements.

My master's thesis is titled “In-situ X-ray Scattering of Spruce Wood with Variation of Load and Humidity”. I performed in-situ X-ray scattering of spruce wood by varying load and humidity to investigate structural changes on the nanoscale. A suitable X-ray transparent chamber was developed which makes measurements at variable strains in a humidity range between 0 and 100% possible. For the wide-angle X-ray scattering (WAXS) signal, an image plate at a sample-to-detector distance of 5.1 cm was used, whereas the small-angle X-ray scattering (SAXS) intensity passed through a hole in the WAXS imageplate and was detected by a second image plate at a distance of 65.6 cm. The microfibril angle and cellulose lattice spacing were evaluated from both SAXS and WAXS intensities. It turned out that the laboratory X-ray intensities are not sufficient to measure a dependence on the strain as successfully reported from synchrotron experiments. However, the influence of humidity could be clearly detected: An increasing crystal lattice spacing was observed and can be explained with swelling of fibrils by absorption of water.

Erhard Schafler, ao. Univ. Prof.

Bulk Nanocrystalline Metals and Alloys

The nanostructuring of bulk metallic materials is obtained by top-down structuring using extremly large strains achieved by plastic deformation under enhanced hydrostatic pressure ("Severe Plastic Deformation, SPD"). Therfore "High Pressure Torsion, HPT" is  primarily used as hydrostatic pressure can be varied and strain can be applied continuously and unlimited. Subsequently the measurement & understanding of the increased mechanical properties (strength, ductility, fatigue strength, fracture thoughness) as a function of grain size and annealing treatment is of main interest.

X-ray Profile Analysis (XPA)

The microstructural features like grain/subgrain-size and -distribution, the dislocation density and also planar lattice defects of nanostructured materials produced by severe plastic deformation but also by other processing routes (electro- and vapor deposition, crystallization from amorphous state,..) are analysed by X-ray Bragg profile analysis. The microstructure is characterised "ex-situ" after processing and/or thermal treatment using an especially designed home laboratory diffractometer but a special focus lies in the devlopment of in-situ experiments using high brilliant Synchrotron radiation.

High Entropy Alloys (HEA)

 These are materials that consist at least of 4-5 alloying-partners/elements in equal amount. Due to Gibbs free energy of formation (ΔG) and the high configurational (mixing) entropy the material may crystallize in one single phase, mostly with high symmetry (fcc or bcc).

The HEAs exhibit high strength, good ductility, increased low temperature deformation properties, good corrosion resistance and also good fatigue properties are predicted. However, many basic principals are not investigated yet, especially with regard to the many different alloys that can be constructed.

Functional properties of nanostructured materials

The improvement of following functional properties of materials by applying by severe plastic deformation is investigated:

  • Hydrogenated nanomaterials: processing by SPD; hydrogen storage, ab- and desorption, stabilization of lattice defects by hydrogen
  • Thermoelectric nanomaterials: chemical synthesis, processing by ball-milling and SPD, structural analysis and characterization, thermoelectric properties

Plasticity of Polymers

The microstructural features and mechanisms of plastic deformation in polymers with semi/nanocrystalline and amorphous structure are investigated with respect to dislocation dominated plasticity in the crystalline phase.

Bogdan Sepiol, ao. Univ.-Prof.

Experimental setup for an aXPCS experiment at the DESY

Experimental setup for an aXPCS experiment at DESY.

My key research area is the study of the properties of materials, like the dynamics (diffusion and phonons) and kinetics of condensed systems, in particular metallic films, intermetallic alloys, as well as metallic glasses and fast ionic conductors, by scattering and by simulation techniques. The focal point is the dynamics of atomic diffusion processes which means the process of atomic movement in solids. The knowledge of these processes is the key to the fundamental understanding of many essential material properties. Important influences are for example how often atoms change their place and to which lattice position they prefer to jump.

The efficient combination of computer simulations and experimental methods like X-ray diffraction make it possible to examine these processes on a whole new level. Especially the extension of the scattering methods to new coherent experimental techniques makes it possible to test theoretical models also on the atomic scale. The measurements are usually done at large-scale research facilities like the ESRF in Grenoble or PETRA III in Hamburg. The radiation available in such facilities fulfills the requirements of coherence, intensity and brilliance which are necessary in these kind of experiments.

Christoph Tietz, PhD student

Typical result of an aXPCS experiment.

Typical result of an aXPCS experiment.

My field of research is the dynamics of amorphous solids on the atomic scale. This is done by the relatively new scattering technique of atomic scale X-ray correlation spectroscopy (aXCPS) based on coherent X-rays. Changes in the microscopic structure of the samples through atomic motion gives rise to changes in the interference patterns called speckles which then can be used to determine atomic motion. aXPCS experiments are done at the 3rd generation synchrotron radiation facilities PETRA III in Hamburg and ESRF in Grenoble. The materials investigated are primarily alkali borate glasses, e.g. rubidium borate x(Rb2O) (1-x)(B2O3). These type of glasses are well known fast ion conductors with possible applications in energy storage. I prepare the glass samples myself in our lab and determine different properties like density, glass transition temperature, etc.

Additionally I perform structure investigations by means of total scattering experiments and computer simulations. This task is necessary in order to extract structure factors needed for modeling of the aXPCS data and to learn more about the microscopic structure of the investigated material. The experiments are either done synchrotrons. Computer simulations include running self-written Monte Carlo simulations of the glasses and refining the potential parameters as well as using Reverse Monte Carlo (RMC) software.

This work is funded by the Austrian Science Fund (FWF): P28232-N36

Katharina Werbach, PhD student

A pin used for the three point bend test.

The aim of my work is the determination of the elastic properties of materials with various experimental methods. Especially ceramics and composite materials are—because of their growing importance for industrial purposes—of particular interest. To determine these properties static as well as dynamic methods are employed.

Micro- and nanoindentation, both static methods, are useful for me because they not only give information about the elastic, but also the plastic properties in a spatially resolved way. Bending tests—also a static method of determining mechanical properties—are particularly useful for the study of composite materials, because filming the experiment allows the investigation of the individual components.

I also use Resonant Ultrasound Spectroscopy—a dynamic method—because it yields information about the elastic behavior of the whole specimen. In this method, ultrasound is used to excite the eigenmodes of a specimen, which allows the simultaneous determination of all elastic constants.

The combination of various methods not only allows me to obtain a detailed picture about the elastic behavior of a material, but also to connect local mechanical properties to global ones.