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Research program

Nanostructured materials: nano-clusters, nano-foams, nano-pillars

Control of the grain-size dispersion is extremely important in the experimental design of nano-structured materials. A nano-structured material with a broad grain-size dispersion will exhibit a lower overall yield/flow stress than a material with the same average grain size but with a much smaller grain-size distribution. To control the defect content and microstructure in nano-structured metallic systems a relatively new approach was explored based on sputtering, i.e. using a so-called magnetron based nanocluster source. Interestingly, the clusters are grown in extreme non-equilibrium conditions, which allow obtaining metastable structures of metals and alloys.

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Laser surface and interface engineering: thick coatings and applications

The surface condition of a component is usually the most important engineering factor. Almost inevitably the outer surface of a work-piece is subjected to wear and corrosion while it is in use. To an increasing degree, therefore, the search is for surface modification techniques, which can increase the wear resistance of materials. In our work two high-power laser techniques are used for the surface engineering of metallic alloys: Laser cladding, which allows the deposition of thick resistant metallic by a melting process fusing a special alloy onto a weaker substrate and Laser hardening, which produces wear resistant tracks by microstructural transformations, i.e. a laser beam scans across a component without melting.

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Advances in microscopy: in situ electron microscopy and scanning probe microscopy

The actual coupling between the microstructure studied by microscopy on one hand and the property of a material is almost elusive. The reason is that these properties are determined by the collective dynamic behavior of defects rather than by the behavior of an individual static defect. However, the situation is not hopeless and we argue that for a more quantitative evaluation of the structure-property relationship emphasis on in-situ measurements is necessary.

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Nanostructured composite coatings: thin films and applications

Nanocomposite coatings: composed of crystalline/amorphous phases mixture are synthesized (PVD and lasers) with unique physical-chemical properties that cannot be attained in bulk materials. By controlling the size and volume fraction of nanocrystalline phases in an amorphous matrix and consequently the separation width of amorphous matrix among the nanocrystallites, the properties of the nanocomposite coatings can be tailored, e.g. to make a balance between hardness and elastic modulus to permit close match to the elastic modulus of substrates, and particularly to obtain high toughness that is crucial for applications under high loading contact and surface fatigue.

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Heterophase and homophase interfaces: fundamentals and applications

This route focuses on the structural aspect of interfaces as a central theme; i.e. it considers mainly the atomic scale with HRTEM and the effects of segregation on in-situ fracture using UHV small-spot SEM/SAM. We have concentrated on the question whether HRTEM image information can be interpreted in terms of the atomic structure and whether the latter will provide information of the bond-strength along the (segregated) heterophase interface between dissimilar materials, like a metal and a ceramic material. It is accurate to say that important properties of materials in high-technology structural and functional applications are strongly affected, even controlled, by the presence of solid interfaces.

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