Finite element modeling of indentation into superhard coatings

Indentation techniques are now widely used to measure the hardness and elastic modulus of surface coatings. In this paper, we applied finite element modeling to simulate the mechanical response of superhard coatings on soft substrates under indentation. In these situations, it was found that the diamond tip cannot be treated as rigid any more. Doerner–Nix method and Oliver–Pharr method were found to give quite different data when applied to derive hardness from the load–displacement curves. The substrate influence was found to be severe even for relatively thick (∼5 μm) coatings. In order to get the film hardness with no substrate influence, indentation experiments should be made within ∼5% the film thickness, rather than the 10% rule-of-thumb.