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PRINCIPAL PUBLICATION AND AUTHORS

Investigation of the microstructure of a graded ZrN/Ti0.33Al0.67N multilayer coating using cross-sectional characterization methods, F. Frank (a), M. Tkadletz (b), C. Saringer (a), C. Czettl (c), M. Pohler (c), M. Burghammer (d), J. Todt (b,e), J. Zalesak (b,e), J. Keckes (b,e), N. Schalk (a), Surf. Coat. Technol. 435, 129126 (2023); https:/doi.org/10.1016/j.surfcoat.2022.129126 (a) Christian Doppler Laboratory for Advanced Coated Cutting Tools at the Department of Materials Science, Montanuniversität Leoben (Austria) (b) Department of Materials Science, Montanuniversität Leoben (Austria) (c) Ceratizit Austria GmbH, Reutte (Austria) (d) ESRF (e) Erich Schmid Institute for Materials Science, Austrian Academy of Sciences, Leoben (Austria)

X-rays probe the microstructure of a graded, multilayer coating for cutting insert applications Cross-sectional X-ray nanodiffraction was employed to assess the microstructure of a protective hard coating utilised in cutting insert applications. A thorough comprehension of stress gradients within these coatings and their correlation with the applied coating deposition parameters is essential for improving overall performance.

One way to enhance the performance of protective hard coatings is to modify the architecture by combining two inherently different materials in a multilayer. Besides the choice of materials, the thickness of the individual layers and residual stress gradients strongly influence the coating s properties.

In this work, a ZrN/Ti0.33Al0.67N multilayer coating with constant Ti0.33Al0.67N and stepwise increasing ZrN

layer thickness (Figure 133a and b) was investigated using cross-sectional synchrotron X-ray nanodiffraction (CSnanoXRD) at beamline ID13 (Figure 133c and d), electron backscatter diffraction and transmission electron microscopy. The aim was to obtain a profound understanding of the microstructure of the coating and the residual stress state. (Semi-)coherent grain growth was observed independently of the ZrN layer thickness. Changes in the multilayer architecture were found to affect not only the grain size, but also the residual stress state. While the grain size increased with increasing ZrN layer thickness (Figure 133b), the residual stress decreased (Figure 133d). In regions with smaller sublayer thickness, higher stress was observed due to dominating coherency strains, which was even more pronounced in the ZrN layers compared to the Ti0.33Al0.67N layers.

The results advance understanding of how sublayer thickness within a multilayered coating influence microstructure and residual stress gradients, paving the way for the design of innovative nanocrystalline coatings.

Fig. 133: Architecture of the ZrN/Ti0.33Al0.67N multilayer coating (a) as planned and (b) as observed by scanning electron microscopy (SEM). c) Phase plot obtained from CSnanoXRD. d) In-plane strain and

stress, as well as unstrained lattice parameter and full width at half maximum across the coating thickness, evaluated for ZrN and Ti0.33Al0.67N from the XRD data.