Simulation of Berkovich nanoindentation experiments on thin films using finite element method

The Finite element technique is applied for studying the very complex stress-strain field of thin hard coatings subjected to a nanoindentation process. Berkovich indentation experiments were simulated with the ABAQUS finite element software package. The investigated system was titanium nitride on high speed steel as an example of a hard film on a softer substrate. The numerical analysis allowed the plastic deformation history during indentation to be followed. In particular, it was possible to correlate the onset of plastic deformation in the substrate with the shape of the loading curve. The system was simulated by an axisymmetric model in which the conical indenter has the same contact area as the Berkovich indenter. A six-fold symmetric three-dimensional model was also defined for testing the suitability of the previous model. The indenter was modeled either as a rigid surface or as a deformable diamond tip. Comparison between the experimental data and numerical results demonstrated that the finite element approach is capable of reproducing the loading-unloading behavior of a nanoindentation test. The film hardness of TiN/HSS specimens was numerically calculated for different indentation depths. It was shown that the presence of the substrate affected the hardness measurement for relative indentation depths greater than about 15% of the film thickness.