Berlin 2018 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 50: Topical session (Symposium EPS and MM): Mechanical Properties at Small Scales

MM 50.1: Topical Talk

Donnerstag, 15. März 2018, 10:15–10:45, H 0106

New Insights into the Ductility of Freestanding Metallic Thin Films — •Benoit Merle — Department of Materials Science and Engineering, Institute I, Friedrich-Alexander-University Erlangen-Nürnberg, Germany

Little is known about the ability of freestanding films to accommodate plastic deformation, which is detrimental to the design of future generations of MEMS and integrated sensors. New insights are provided by investigations on 100-300 nm PVD copper, gold and silver thin films by means of in-situ tensile tests in a TEM and in-situ bulge tests in an AFM. They revealed that small specimens can accommodate a remarkable level of strain (10% or more) due to the grain-boundary mediated dominated deformation and the associated high strain-rate sensitivitya. This is in sharp opposition to the behavior of larger samples, which typically fail around 1% strain, because they contain defects that act as crack initiators. Suppressing them at all is hardly achievable in practice, which is why the most promising strategy to improve the ductility of thin films consists into improving their resistance to fracture. The bulge test offers a convenient way to measure the fracture toughness and observe the associated mechanisms. Against expectations, it was found that the thickness hardly influences the toughness of the films within the investigated range and that the microstructure does not play such a critical role as assumed. The resistance to fracture was shown to mostly depend on the resistance to necking ahead of a crack tip, suggesting new possibilities to increase the ductility of the films.