Nanoindentation studies of brittle thin films on a titanium alloy substrate

The mechanical properties of a range of tribological mitigating and biocompatible films deposited on a titanium alloy substrate have been investigated using nanoindentation. For a range of carbon films investigated, the ratio of hardness to modulus was almost constant at around 0.1. The onset of film-substrate interactions of a coated system upon progressive loading could be determined as the depth of penetration at which the slope of the force versus depth curve deviated from that of an analytically derived "bulk film" system that incorporated the indenter tip effect on the contact area. For the carbon-coated systems investigated, the corresponding force, or the critical load-carrying capacity of a localized contact event by a sharp indenter, appears to scale with the elastic modulus mismatch between film and substrate.