Wolfgang Kurtz

Temperature dependence of faceting in Σ5(310)[001] grain boundary of SrTiO3

Abstract Using high-resolution electron microscopy (HREM), temperature dependence of faceting of an asymmetric Σ5 grain boundary (GB) in SrTiO 3 is observed. The bicrystal samples have been fabricated by ultra-high vacuum diffusion bonding and heat-treated between 1100 and 1600 °C. Below 1300 °C, this GB facets into symmetric (310) and asymmetric (100)//(430) GB planes. At 1300 °C, in addition to the asymmetric facet, the symmetric {210} facet appears: three different facets are thus observed at this temperature. At 1400 and 1500 °C, the asymmetric facet disappears and the two kinds of symmetric facets remain. At 1600 °C, faceting disappears and the GB becomes defaceted. The faceting/defaceting transition behavior of the GB is interpreted in terms of the Wulff plot and its corresponding equilibrium crystal shape.

Current work at the Stuttgart UHV diffusion bonding facility

Abstract The Stuttgart ultra-high-vacuum (UHV) diffusion bonding facility serves to produce high-quality solid solid model interfaces. An overview is givef on the more recent work comprising bicrystals of metal–metal, ceramics–ceramics, and metal–ceramics combinations. Orientation errors below 0.1° have been obtained routinely with sapphire–sapphire bicrystals. The bi- and tricrystals produced serve as samples for mechanical testing and as specimens for both analytical and quantitative high-resolution electron microscopy. The close control of the interface chemistry allows for segregation studies and studies of the influence dopants have on the interface properties. UHV diffusaon-bonded low-angle grain boundaries present arrays of edge or screw dislocations of just one type and thus facilitate investigations of these dislocations and their core structures.

Bonding between Cu and α-Al2O3

Abstract This ongoing study aims to investigate systematacally the influence of surface preparation methods on the bonding between Cu and α-Al2O3. High-spatial-resolution electron energy-loss spectroscopy and high-resolution transmission electron microscopy were used to study Cu/α-Al2O3 interfaces produced by molecular beam epitaxy and diffusion bonding. Our results show that the preparation of the Al2O3 surface can affect the interfacial bonding considerably. Only very weak adhesion between Cu and Al2O3 could be obtained for an Al2O3 substrate subbected to a chemical cleaning procedure followed by annealing. Ar+ ion pre-sputtering of the Al2O3 led to much stronger adhesion. Intermetallic-like interfacial bonding was observed in the samples on Al2O3 substrates annealed in ultra-high vacuum after pre-sputtering; whilst in the samples on Al2O3 substrates annealed in oxygen after the pre-sputtering, no significant bonding formed. High temperature and pressure applied in diffusion bonding production were not ...

HVEM in situ study of fracture of Al2O3/Nb sandwich specimens

Abstract In situ straining experiments on α-Al2O3/Nb/α-Al2O3 single crystal sandwiches have been performed in a high-voltage electron microscope in order to observe the dislocation motion connected with the fracture of these samples. The tricrystals had two different orientation relationships at the interfaces, both possessing high fracture energies. The in situ studies showed that the fracture occurs along the interfaces but more frequently inside the Nb sheet. The fracture is connected with strong plastic deformation. The crack opening and the dislocation processes are analysed.

Segregation of Yttrium at Grain Boundaries in α-Al 2 O 3

Quantitative X-ray analysis allows the investigation of yttrium-doped grain boundaries. In the present study well-defined bicrystal interfaces were characterized. The quantitative comparison of segregation at different bicrystals requires a correction of artifacts in the X-ray spectra due to mass absorption, fluorescence, and beam spread. Mean grain boundary excess values of 3 Y/nm 2 and around 5 Y/nm 2 were found at a ∑17 and ∑37 symmetrical grain boundary, respectively. Additionally, with the ∑17 bicrystal YAG precipitation and presence of silicon was found.