Micro-structural and -mechanical characterisation of Cu-based foils using electron backscatter diffraction, bulge testing and instrumented indentation

The derivation of mechanical properties from freestanding metallic foils requires establishing tailored characterisation methods. This study presents a novel methodology for a comprehensive mechanical characterisation of micrometric-thickness Cu-based thin foils (13 - 27 μm). The approach combines Focused Ion Beam-Electron Backscatter Diffraction (FIB-EBSD) for microstructural analysis, Bulge Testing (BT) for macroscopic material properties, and Instrumented Indentation Testing (IIT) for local mechanical behaviour. The effects of alloying elements (Ni, Zn), manufacturing and thickness on the elastoplastic properties of Cu (Phosphorous High- Conductivity PHC, 99.95 % wt.) were evaluated, as well as their influence on the microstructural and mechanical properties. The methodology was successfully applied to and validated for Cu-based foils, demonstrating feasibility and good agreement with the literature for elastic and plastic properties. Microstructure significantly influenced the mechanical properties of Cu-based foils. Adding Zn and Ni in Cu15Zn and Cu18Ni20Zn alloys delayed recrystallisation, while strengthening the alloyed foils compared to pure Cu and decreasing ductility. Increasing the grain size to foil thickness ratio reduced flow stress and ductility. BT proved the most suitable technique to determine plastic properties, while IIT provided reliable elastic modulus, hardness, and elastic/plastic indentation work.