Deformation modes of nanostructured thin film under controlled biaxial deformation

This paper reports on the mechanical behaviour of nanostructured W/Cu thin films deposited on Kapton® under controlled biaxial loadings thanks to a biaxial testing device developed on DiffAbs beamline at SOLEIL synchrotron (Saint-Aubin, France). In situ tensile tests were carried out combining 2D synchrotron X-ray diffraction (XRD) and digital-image correlation (DIC) techniques. First, the elastic behaviour of the composite metallic film — polymeric substrate was investigated under equi-biaxial and non-equi-biaxial loading conditions. The results show that the strain measurements (in the crystalline film by XRD and the substrate by DIC) match within 10− 4. This result demonstrates the full transmission of strains in the elastic domain through the film-substrate interface and thus a good adhesion of the thin film to the substrate. The second part of the paper deals with higher strains response under equi-biaxial tensile tests. The elastic limit of the nanostructured W/Cu thin films was determined at the bifurcation point between strains obtained by XRD and DIC. Deformation mechanisms such as strain localisation and film fragmentation are proposed.

► Deformation of nanostructured W/Cu thin films on polymer studied by biaxial loading. ► Strains in the film and the substrate match within 10− 4 in the elastic domain. ► Full strain transmission through the film–substrate interface in the elastic domain. ► Good metallic film adhesion to the polymer is obtained without substrate treatment. ► The high elastic limit of the films (up to 0.5%) is due to the residual stresses.