Experimental and simulative strain field investigation of nano- and microscratches on nanolaminated (Cr, Al)N coating

• Micro- and nanoscratches were created on a nanolaminated CrN/AlN sample.
• Vertical strains under the scratch were determined via scanning electron microscopy.
• The results are compared with those of finite element simulations.
• The appearance of lateral microcracks is correlated with strong shear stresses.
• A previously reported stress–strain determination methodology is validated.

Micro- and nanoscratches were made on a nanolaminated CrN/AlN coating under different loads and velocities. The remaining vertical strain fields under the scratches were determined by measuring the bilayer periods in cross-fracture images using scanning electron microscopy. These results were compared with the remaining vertical strain fields obtained from scratch simulations utilizing the strain-rate-dependent material properties examined in preliminary work. The effect of the friction coefficient and residual stress on the strain and stress fields was investigated using simulations. The experimental and simulated strain fields show good quantitative agreement for the nanoscratches. Furthermore, the appearance of fractures and microcracks under the scratches could be correlated with strong shear stresses in simulations during indenter overrun. This method and the results obtained enable the stress–strain fields of coatings under dynamic mechanical loads to be determined quantitatively. Additionally, the possibility of determining failure criterions using scratch tests enables the simulative prediction of a coating's resistivity under real loading conditions.