Structural Characterization of Nanoindentations

The development of new advanced materials and the advent of mechanical devices at the micrometer scale require knowledge of the material behaviour at the micro- and nanometer scale. Different mechanisms are known influencing the deformation behaviour and the mechanical properties at small material volumes. Miniaturized mechanical systems are of growing importance in medical applications, in robotics and in electro-mechanical devices. For a successful design of such mechanical systems the materials response to loads at this length scale is important. New advanced materials consist frequently of several phases, whereas the size of these phases in at least one dimension is commonly in the micro- and nanometer regime (e.g. nano composites, fully lamellar TiA1, et cetera). These materials have improved properties with respect to strength and ductility over common materials and are important, e.g. for the transport and aerospace industry. There is an essential link between the macroscopic material behaviour and the macroscopic processes. In order to understand and improve the macroscopic mechanical behaviour the local deformation mechanisms in the micro- and nanometer regime (e.g. plastic deformation around small hard particles) have to be known. Indentation tests are a simple way to test the elastic and plastic properties of materials an different length scales (micro-, micro- and nanohardness). At small indentation depths in the range of several 100 nm an indentation size effect has been found, i.e. the hardness increases with decreasing indentation depth. This effect is attributed to a change in the local deformation structure at small indentations. Investigating both, the mechanical properties and the resulting microstructure simultaneously deliver this essential link. Several experimental setups will be used (e.g. indentations to different depths in different oriented grains, indentations in the vicinity of grain boundaries and hard particles) in order to investigate the influence of certain constraints an the deformation behaviour. Additionally, models will be developed to describe the mechanical behaviour of materials in the micro and nano scales. Furthermore, the experimental results will be compared with simulations from a previous project and from the literature. The aim of the proj ect is to provide a better understanding of the size effect and the basic plastic deformation mechanisms in small volumes (under extreme constrains).