FWF- Defects and structural anisotropy in ultrafine-crystalline metals

In this project the correlation between the anisotropy of the microstructure and the characteristics of defect annealing in ultrafine crystalline metals could be identified and quantitatively analyzed using the specific experimental technique of high precision length measurements (dilatometry) in combination with structural characterization by neutron diffraction and scanning electron microscopy. Among others, the volume of the relaxed lattice vacancy – a fundamental structural parameter in condensed matter physics – could be determined experimentally. The access to anisotropic, i.e., orientation-dependent processes revealed to be the outstanding advantage of dilatometry compared to other techniques of thermal analysis.

The ultrafine crystalline metals with grain sizes in the regime of 100 nanometers (i.e., one tenth of a micrometer) were produced by techniques of severe plastic deformation (SPD), so-called equal channel angular pressing and high-pressure torsion. The processes of structural refinement by severe plastic deformation as well as the particular mechanical behaviour of this attractive class of materials are intimately related to their structural defects which are available in highly abundant concentrations and which were in the focus of this project.

A model could be proposed and successfully tested for directly determining the volume of lattice vacancies by means of dilatometric measurements of the orientation-dependent length change. Furthermore, kinetic diffusion models were developed quantitatively describing the length change due to the annealing out of deformation-induced free-volume type defects. These model tools are considered to be of more general interest going beyond the scope of SPD-metals.

Neutron diffraction and difference dilatometry clearly indicated that the observed anisotropy in length change upon defect annealing is solely attributable to the microstructure rather than to internal stresses. The examined close correlation between structural anisotropy and the anisotropic annealing of excess volume yielded – apart from the vacancy volume – also direct access to the grain boundary excess volume, a further key parameter in materials science.

The project was performed in close cooperation with groups of the Erich-Schmid Institute (OeAD and University of Leoben), the research neutron source Heinz Maier-Leibnitz (TU Munich, Garching, Germany), the Austrian Institute of Technolgy (AIT, Wiener Neustadt), the Institute of Materials Physics of the University of Münster (Germany), and the Institute of Electron Microscopy and Nanoanalytics of TU Graz.

In this project the correlation between the anisotropy of the microstructure and the characteristics of defect annealing in ultrafine crystalline metals could be identified and quantitatively analyzed using the specific experimental technique of high precision length measurements (dilatometry) in combination with structural characterization by neutron diffraction and scanning electron microscopy. Among others, the volume of the relaxed lattice vacancy a fundamental structural parameter in condensed matter physics could be determined experimentally. The access to anisotropic, i.e., orientation - dependent processes revealed to be the outstanding advantage of dilatometry compared to other techniques of thermal analysis. The ultrafine crystalline metals with grain sizes in the regime of 100 nanometers (i.e., one tenth of a micrometer) were produced by techniques of severe plastic deformation (SPD), so-called equal channel angular pressing and high-pressure torsion. The processes of structural refinement by severe plastic deformation as well as the particular mechanical behaviour of this attractive class of materials are intimately related to their structural defects which are available in highly abundant concentrations and which were in the focus of this project. A model could be proposed and successfully tested for directly determining the volume of lattice vacancies by means of dilatometric measurements of the orientation-dependent length change. Furthermore, kinetic diffusion models were developed quantitatively describing the length change due to the annealing out of deformation-induced free-volume type defects. These model tools are considered to be of more general interest going beyond the scope of SPD-metals. Neutron diffraction and difference dilatometry clearly indicated that the observed anisotropy in length change upon defect annealing is solely attributable to the microstructure rather than to internal stresses. The examined close correlation between structural anisotropy and the anisotropic annealing of excess volume yielded apart from the vacancy volume also direct access to the grain boundary excess volume, a further key parameter in materials science. The project was performed in close cooperation with groups of the Erich-Schmid Institute (OeAD and University of Leoben), the research neutron source Heinz Maier-Leibnitz (TU Munich, Garching, Germany), the Austrian Institute of Technolgy (AIT, Wiener Neustadt), the Institute of Materials Physics of the University of Münster (Germany), and the Institute of Electron Microscopy and Nanoanalytics of TU Graz.