Abstract
Nanoindentation of treated surfaces, thin films, and coatings is often used as a simple method to measure their hardness and stiffness. These quantities are technologically highly relevant and allow to qualitatively compare different material and surface treatments but fail to capture the entire extent of the highly complex mechanical interaction between indenter tip and the tested surface. Many studies have addressed this question by analytical or numerical modeling, but they must rely on verification by recalculating indentation curves or ex situ microscopy of surface deformation postexperiment. Herein, results from in situ measurements of the multiaxial stress distributions forming beneath an indenter tip while the tested sample is still under load are presented. A 9 μm‐thick TiN hard coating is tested in 1) as‐deposited state and 2) shot‐peened by Al2O3 particles, using two diamond wedges as indenter tips, with 60° and 143° opening angle, respectively. The results reveal a strong influence of the tip shape on the deformation behavior and the main stress component developing inside the sample while under load. In addition, a crack‐closing effect can be attributed to the exponentially declining near‐surface compressive residual stress gradient that is present in the shot‐peened sample.
Highlights
Sample PreparationThe %9 μm-thick TiN hard coating was deposited onto a ferritic steel substrate in an industrial-scale plasma-assisted chemical vapor deposition plant manufactured by Rübig (Wels, Austria) using the process gases TiCl4, H2, N2, and Ar, mixed by mass flow controllers
Nanoindentation of treated surfaces, thin films, and coatings is often used as a and preexisting near-surface stress state of simple method to measure their hardness and stiffness
The 9 μm-thick TiN thin film investigated in this work features a nanocrystalline microstructure with columnar grains and a fiber texture.[9]
Summary
The %9 μm-thick TiN hard coating was deposited onto a ferritic steel substrate in an industrial-scale plasma-assisted chemical vapor deposition plant manufactured by Rübig (Wels, Austria) using the process gases TiCl4, H2, N2, and Ar, mixed by mass flow controllers. Halfway through the deposition process, the substrate temperature was raised rapidly from 813 to 853 K, resulting in two sublayers with slightly differing film microstructures and residual stress levels Up to this point, the sample is the same as described in the previous study by Zeilinger et al.,[9] but for this work, the TiN hard coating was subjected to a shot-peening treatment using a pressure of 400 kPa and a spherical blasting medium of Al2O3 particles, 50 μm in size. The sample is the same as described in the previous study by Zeilinger et al.,[9] but for this work, the TiN hard coating was subjected to a shot-peening treatment using a pressure of 400 kPa and a spherical blasting medium of Al2O3 particles, 50 μm in size This treatment resulted in compaction and smoothing of the coating’s surface, as well as the introduction of near-surface compressive residual stress.[17]
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