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| Book/Dissertation / PhD Thesis | FZJ-2025-04401 |
2025
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-95806-861-2
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Please use a persistent id in citations: doi:10.34734/FZJ-2025-04401
Abstract: In recent years, there has been a notable increase in interest in cold spraying, largely due to its potential applications in repair and additive manufacturing. Nevertheless, further research is required to gain insight into the residual stress state and mechanical integrity of cold sprayed coatings. This thesis is concerned with the repair of Inconel 718 components. Such components are employed in gas turbines and other applications due to their exemplary material properties. In this context, a cavity was created, based on the typical repair process, with a depth of 4 mm and 60° conical walls, as a result of the milling process, for the purpose of crack removal. The filling of such deep cavities with Inconel 718 results in the formation of a dense coating with good adhesion. A comprehensive residual stress analysis of the entire cavity was conducted using neutron diffraction, with near-surface measurements supplemented by the incremental hole-drilling method. The resulting residual stress state was found to be direction-dependent due to the geometric limitations of the cavity, as expected, but the specific gas conditions showed the anticipated results. Further experiments were conducted to investigate the effects of different robot speeds by in situ curvature measurements using the ICP sensor. Based on the findings, an analytical model was developed to estimate the resulting temperature gradient at the gas spot. These findings are supported by particle diagnostics and data from an implemented, three-dimensional CFD model in ANSYS Fluent. The results were also used to vary the resulting spray spot of different nozzle geometries in the context of additive manufacturing and to discuss the resulting residual stresses in conjunction with the data pertaining to the gas and particles. The results demonstrate that the restoration of Inconel 718 components by means of cold spraying results in the formation of dense repair coatings with good mechanical properties. The residual stress state is anisotropic, depending on the geometric limitations. In general, it is possible to systematically adjust the residual stress state in cold sprayed coatings by modifying the process parameters and the nozzle geometry in order to achieve the desired stress state. The present work was carried out within the framework of the DFG project VA163/11-1.
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