Resolving depth evolution of microstructure and hardness in sputtered CrN film

• Effect of local microstructure on hardness and elastic modulus of sputtered CrN.
• X-ray nanodiffraction reveals microstructure changes due to varying ion bombardment.
• Depth-gradients obtained by nanoindentation on wedge-shaped film sample.
• Growth-related hardness gradient due to varying crystallite size and defect density.
• Elastic modulus determined to be almost constant due to isotropic film response

Hardness and elastic modulus of a sputtered nanocrystalline CrN thin film, prepared under varying ion bombardment conditions, were studied by nanoindentation using a depth-profiling technique and related to cross-sectional X-ray nanodiffraction data on the local microstructure. Changes in texture are shown to have almost no effect on the elastic modulus due to the isotropic response of the polycrystals. However, the locally varying growth conditions, which affect the crystal size and the number of defects in the film, determine the hardness values across the film thickness. Regions with highly distorted small crystals result in higher hardness in comparison with those with well-developed coarsened grains. This study confirms the notion of the existence of growth-related hardness gradients in single-phase nanocrystalline thin films.