Elementary mechanisms

The amorphous structure of metallic glasses is at the origin of their peculiar mechanical properties. The most impressive are for instance their very high yield strengths (from 1500 to as high as 3000 MPa) as well as their very large elastic deformation ability (up to 2%). Their are in general however poorly ductile at room temperature, at least in tension. One of the major challenge in the scientific community is to understand the relationship between their structure and how this latter evolve during their deformation, both in the elastic and in the plastic regime as well as how they fail. The mechanical responses of these materials depend obviously on their compositions but more interestingly also on less intuitive characteristics such as their sizes or their deformation histories, even in the elastic regime.

Left: Thin metallic ZrNi amorphous thin film specimens were produced by PVD in collaboration with the IMAP Laboratory in Belgium (Université Catholique de Louvain) and tested in tension thanks to the "micro-machine" technology. Surprisingly, specimens of thicknesses below 500 nm were found to exhibit higher yield strength as well as giant ductility (up to 14 % !) inducing the idea of "the smaller, the better" (Matteo Ghidelli thesis, Acta. Mat. Paper). To go further in the understanding of such mechanical properties, preliminary tests using a nano-focused X-ray beam (ESRF-ID01 beamline) were performed in order to probe and map the local deformation at a sub-micron scale and see how it correlates with the macroscopique deformation.

Right: In this case, 3 mm diameter rods of a Zr-based bulk metallic glasses were processed by arc-melting followed by suction casting and room temperature compression tests with differents pre-loading stages (0, 3 or 7 load cycles at 20 % of the yield strength). The results show that structural modifications, called "rejuvenation" in the litterature, and therefore different macroscopic deformation capacities can be induced by a few small pre-sollicitations in the elastic regime. The very nature of these features remains however still unknown.