In-situ determination of mechanical failure modes in thin mono- and multilayer coatings

Mechanical properties such as fracture strength and fracture toughness of thin films obtained from Physical Vapour Deposition are difficult to evaluate since the relative small dimension of such coatings. Furthermore, the fracture modes are not well understood yet. In this thesis novel techniques have been used in order to fill the lack of information about mechanical properties of hard thin coatings. In-situ bending tests were carried out in order to study the fracture strength. The evaluation of such property and the modes of fracture were studied via direct observation inside the Scanning Electron Microscope (SEM) during the loading. A comparison with traditional techniques such as Load Bearing Capacity (LBC) and nanoindentation is also presented. Another novel technique was used in order to test thin coatings avoiding the effect of the substrate: micropillar compression. Pillars were milled inside the coatings using a Focus Ion Beam (FIB) instrument and then compressed using an indenter inside the electron microscope. Using this technique, stress-strain curves were obtained. Furthermore, the fracture modes were analysed during the loading. Also in this case a comparison with LBC is discussed. Both techniques reveal to be useful to evaluate fracture mechanisms of the films, especially for multilayer films.