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Microscopy study of advanced engineering materials

Crystallography and methodology
PhD ceremony:Mr L.T.H. (Leo) de Jeer
When:January 12, 2018
Supervisor:prof. dr. J.T.M. (Jeff) de Hosson
Co-supervisor:ir. V. (Václav) Ocelik, Dr PhD
Where:Academy building RUG
Faculty:Science and Engineering
Microscopy study of advanced engineering materials

This research concentrates on the change in microstructure by (industrial) processing in advanced engineering materials. Crystals are the building blocks of metals and their orientation plays an important role in mechanical and oxidation behaviour. With Electron Backscatter Diffraction (EBSD) we mapped the change of the crystal orientation distribution, or texture, in a material on a global and a local scale. In this thesis, the crystallographic change of different complex materials were studied and linked to physical mechanisms. We studied the deformation, heat treatment and oxidation of AISI 420 stainless steel; production of nanoporous gold by dealloying and quenched Al0.7CoCrFeNi.

Industrial processes change the texture and this was studied in detail for deformation and heat treatments. On the surface, we conclude that highly deformed sites on the steel are a good indicator for predicting places where oxidation starts and that the oxidation rate depends greatly on the crystallographic plane at the surface.

By dealloying gold-silver foils, nanoporous gold foils are obtained. The violent process of dealloying leaves the material with a better fitting of the crystals and an enhanced texture on a local and global scale due to reorganization of the gold atoms.

For Al0.7CoCrFeNi, a five element alloy with only two crystal phases, the crystal orientation relationship on the boundary of the phases was studied. A relationship is common due to the fitting of the crystals; however in this case a continuum between two theoretical relationships is found. This effect is attributed to local variation in composition in the material.