Derivation of tensile flow properties of thin films using nanoindentation technique

By regarding the tip blunting as a ball indentation at very low depth range (within about 80 nm in our experiments), the flow properties of Au thin films were derived from the indentation load–depth curve obtained by nanoindentation technique. The effects of pile-up or sink-in were considered in determining the real contact between the indenter and the specimen. The representative strain in indentation was defined in various ways and examined by comparing the flow properties derived from indentation load–depth curve with those measured by tensile test. The best definition was found to be the shear strain at contact edge multiplied by 0.1. When we considered the effects of pile-up or sink-in, the representative stress in indentation could also be determined, and was found to be one third of the mean contact pressure for fully plastic regime. As a more intrinsic property than hardness, the yield strengths of Au films with thickness of 0.56 and 0.99 μm were extrapolated from the derived true stress–true strain curve as 261±30 and 154±18 MPa, respectively.