The effect of specimen roughness and indenter tip geometry on the determination accuracy of thin hard coatings stress–strain laws by nanoindentation

Nanoindentation, conducted using devices with enhanced accuracy and capabilities, contributes to the reliable characterization of coatings and other material mechanical properties. Herein there are many parameters that significantly affect measurement reliability and thus may lead to errors in the evaluation of results. Such parameters include specimen roughness and geometrical deviations (due to manufacturing tolerances) in the indenter tip form. In earlier investigations, the actual tip geometries of various indenter types were approached with the aid of a continuous simulation of the nanoindentation using finite element method modeling techniques that enable the determination of material stress–strain characteristics. In the present paper, the application of this method—further improved to define the constitutive laws of thin hard coatings—is described, wherein the effect of specimen roughness on the accuracy of the indentation results is taken into account. Furthermore, the results introduced show that the defined material elastoplastic deformation characteristics, based on the nanoindentation test results, are independent of the indenter type (Vickers or Berkovich) when deviations in the indenter tip geometry from the ideal are considered.