Keywords: bulk nanomaterials, instrumentation, simulation, mechanical properties, polycrystalline materials, diffraction, thin films, elastic deformation, plastic deformation, microstructure, fabrication, tensile testing, nanoindentation, atom probe tomography, nanocomposites, nanotechnology
Small scale mechanical properties of polycrystalline materials: in situ diffraction studies
The recent developments in the fields of processing, mechanical characterisation as well as simulation allow for a deeper study of the relationships between the microstructure and the mechanical properties of nanostructured materials (thin films and bulk nano materials). The understanding of size effect on the elastic and plastic deformation mechanisms is of both fundamental and practical interests in particular for the optimisation of industrial applications. Understanding of the relationships between their fabrication, microstructure, and mechanical properties is also fundamental. In particular, one of the key factors is related to the deformation mechanisms responsible of the elevated mechanical properties of such materials. In situ structural studies during deformation process allow quantifying the strain stress relationship of nanomaterials in the elastic and plastic regimes in relation with the microstructure since the spacing d of the material is used as a strain gage. Due to the very small dimensions of the crystallites, very intense sources are necessary such as neutron reactors for bulk nanomaterials and synchrotrons for nanostructured thin films and bulk nanomaterials. For more than a decade, our group has developed in situ tensile testing in diffractometers at the laboratory using rotating anodes as X-ray sources or at dedicated beam lines of synchrotron and Neutron facilities such as LURE (France), ESRF (France), PSI (Switzerland), ALS (USA or in a near future SOLEIL (France). A close connection has been made recently with this last facility through an ANR-Pnano project called Cmonano. In addition, local analyses are done using nanoindentation for intrinsic mechanical properties and atom probe tomography for structural characterisation. Atomistic and molecular dynamics simulations are completing the instrumental study. This paper will give an overview of the subject considering recent experiments on nanometric multilayers (WCu) and thin films (MoCr) encountered in micro electronic applications as well as bulk CuNb and CuTa nanocomposites processed by severe plastic deformation.