Boryana Rashkova

Sample Preparation by Metallography and Focused Ion Beam for Nanomechanical Testing

Abstract Mechanical size effects in micron and submicron scale sample testing are of immense interest in materials science. In this work, we report on a combination of structured chemical etching and focused ion beam fabrication to allow site specific and time efficient fabrication of miniaturized specimens for mechanical testing. Further, we demonstrate the applicability of these samples for quantitative in situ experiments in the scanning and transmission electron microscopes.

Influence of heat treatment on the microstructural evolution of Al–3 wt.% Cu during high-pressure torsion

Solution-treated, peak-aged and overaged samples of the model alloy Al–3 wt.% Cu, obtained by selective heat treatments of the pre-material, have been subjected to high-pressure torsion at room temperature and at 200 °C. The mechanical behaviour of the samples was investigated with torque measurements during deformation and microhardness measurements after deformation. Irrespective of the initial material condition, in the saturation regime a comparable equilibrium microstructure was found consisting of ultrafine aluminium grains stabilized by precipitates formed at grain boundaries.

Microstructural evolution and grain refinement in an intermetallic titanium aluminide alloy with a high molybdenum content: Paper presented at “XV International Conference on Electron Microscopy”, 15–18 September 2014, Cracow, Poland

Abstract As a strong β-stabilizing alloying element, Mo has gained importance for intermetallic β/γ-TiAl alloys. In general, TiAl alloys containing a significant volume fraction of the disordered body-centered cubic β-phase exhibit improved processing characteristics during hot-working. To increase the understanding of the alloying effect of Mo, a model alloy with the chemical composition Ti-44Al-7Mo-0.1B (in at.%) was investigated. In this work, the microstructural evolution after individual heat-treatment steps was studied by means of scanning as well as conventional and in-situ transmission electron microscopy. Additionally, macro-hardness and nanoindentation measurements were conducted to study the change in hardness due to grain refinement and solid-solution hardening. The variation of the observed macro- and nano-hardness corresponds well with the microstructural evolution. The obtained grain refinement effect leads to a significant increase in the macro-hardness, whereas the increase in the average nano-hardness of the individual phases is related to solid-solution hardening.

Metallography - A Powerful Instrument for Material Characterisation, Material Development and Failure Analysis

A. Widmanstätten (1754-1849) was one of the first scientists who developed techniques for studying the microstructure of meteorites by grinding and etching them with nitric acid. Also H.C. Sorby (18261908) used such methods for microstructural investigations of minerals and rocks to identify their origin, as well as to examine steels and meteorites. Other famous and nowadays well known researchers such as R. Hadfield (1858—1940), A. Martens (1850-1914), E.C. Bains (1891-1971), K.H. Ledebur (18371906), and H. Brearley (1871-1948) further developed these basic methods to get more information about the microstructure, especially in case of steels. Many microstructural parts or phases of the FeFe3C phase diagram are called in honour of these scientists, e.g., “Widmanstätten ferrite”, “Sorbite”, “Bainite”, “Martensite”, or in case of cast iron “Ledeburite”.