Mechanical properties of hard AlCrN-based coated substrates

The present investigation has been conducted in order to study three commercially available hard AlCrN-based coated substrates by means of nano- and microindentation, aimed at determining the intrinsic hardness of the films. The results obtained are subsequently discussed taking into consideration the residual stresses and structure (grain size and texture) determined by X-ray diffraction and in the light of published data available in the literature. The study is first carried out with monolithic CrN and AlCrN coatings and it is further extended to the analysis of multilayer AlCrN/TiSiN coatings. Hardness obtained from nanoindentation at low depth and modelling the microindentation data match with values obtained at 22, 30 and 31 GPa for CrN, AlCrN and AlCrN/TiSiN coatings respectively. Residual stresses change from slightly tensile for CrN coating to highly compressive for AlCrN and AlCrN/TiSiN ones while the average grain sizes neglecting microstrains are similar for the three coatings (10–15 nm). AlCrN and AlCrN/TiSiN response similarities result from the low influence played by the stratification as compared to the nanostructure of the polycrystalline sublayers (nanometric grain size).