Deviations in determining coatingsʹ and other materialsʹ mechanical properties, when considering different indenter tip geometries and calibration procedures

In the ISO 14577-4 standard various procedures for estimating the indenter area functions and the frame compliance Cf are proposed. Recently, a FEM-supported method performing a stepwise, trial and error simulation of nanoindentation, enabled the determination of materials stress–strain laws and moreover the precise mathematical description of an equivalent indenter tip geometry. An evolution of this method is presented in this paper, allowing the definition of the exact indenter inclination angle and of the indenters’ area functions as well (TiGAF algorithm: Tip Geometry & Area Function). Various materials, including coatings, Silicon (100), glass BK7, fused silica, tungsten, steel, etc were tested by nanoindentations and the related results were used to determine the indenter area functions, according to the aforementioned procedures by the TiGAF algorithm and after ISO14577-4 (method 3). A comparison of the obtained results revealed a good agreement. Furthermore, an effort to approach the stress–strain curves of a TiAlN coating, by assuming various indenter tip geometries, was realized by employing appropriate FEM-based techniques. The application of indenter tip geometries diverging from the determined one by the TiGAF algorithm led to significant deviations of the different stress–strain characteristics from the nominal ones.