Nanoindentation is routinely used to determine local mechanical properties of materials such as hardness and Young’s modulus. Especially for the testing of thin films, nanoindentation is used on materials approaching hardness close to diamond, the indenter tip's material. Yet, the correlation between the deformation of the indenter and the stress-strain evolution within sample remains still unknown.
Contrary, in-situ cross-sectional X-ray nanodiffraction (CSnanoXRD) coupled with indentation has given new insights into the elasto-plastic deformation of thin films during indentation. To test the mechanical response of the indenter tip, a diamond wedge indenter tip with a radius of 2µm was coated with a 3.8µm thick diamond thin film using hot-filament chemical vapour deposition. Focused ion beam milling at the edges of the wedge ensured uniform signal during the CSnanoXRD experiment. In following, the in-situ indentation setup was used to determine experimentally the multi-axial stress distributions across both the diamond-coated indenter and the tested nanocrystalline diamond with a resolution of 80nm. The multi-axial stress results yielded a maximum stress of -13GPa evaluated in direction of contact. Detailed stress analysis revealed accumulation of residual stress gradients both in the diamond indenter tip and sample up to depths of 1µm after the experiment. The results give unprecedented insights into the deformation of both indenter and tested material.