Effets d'échelle sur le comportement mécanique des verres métalliques – MEGAPROSE

Metallic glasses share with some other nanomaterials exceptional mechanical properties and in particular an elastic limit approaching the theoretical limit. Their main drawback is their almost complete lack of homogeneous plastic deformation at room temperature, which limits their industrial application. In order to develop new metallic glasses with improved characteristics, a better understanding of their deformation mechanism is required. It is known that at room temperature, the plastic deformation is localized in shear bands, but the origin of latter is still a matter of debate, especially the first steps of their development. Moreover, since metallic glasses have no long-range order, no size effect is expected during their plastic deformation, i.e. their deformation should be independent to the sample size. This expectation was recently contradicted by experiments that showed that the plastic deformation increases when one sample dimension gets below few microns [C. J. Lee, J. C. Huang, T. G. Nieh, Applied Physics letters, 91 (2007) 161913]. Even if the cause for this size effect is not known, it might be directly related to a characteristic length scale in the deformation processes, possibly the critical size above which a growing shear band becomes unstable (considering that the fabrication process of such small sample doesn't modify the mechanical behaviour). In the present project, we aim to study the size effect on the mechanical behaviour of metallic glasses and use the link between size and deformation process to better understand the first steps of shear band formation. The project is based on a combination of experiments and simulations. We will deposit thin films of metallic glasses of various widths using microelectronic techniques. The location of Grenoble is a great advantage thanks to the proximity of clean room facilities (especially the PTA 'Plateforme de Technologie Amont'), of MINATEC and because of the 'pôle de compétitivité' Minalogic. Some micro-testing systems will be developed and used. In order to get a local view of the deformation mechanism, in-situ TEM characterisation will also be performed. At the same time, we want to adapt to metallic glasses a very innovative auto-actuated testing system that was recently developed at Louvain-la-Neuve to test the mechanical properties of crystalline samples of sub-micron size. Finally, we will use molecular dynamics simulations to link the experimental results to the local atomic behaviour.