Correlation of Microstructure and Properties of Cold Gas Sprayed INCONEL 718 Coatings
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Correlation of Microstructure and Properties of Cold Gas Sprayed INCONEL 718 Coatings R. Vaßen1 • J. Fiebig1 • T. Kalfhaus1 • J. Gibmeier2 • A. Kostka3 S. Schru¨fer4
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Submitted: 30 October 2019 / in revised form: 21 January 2020 Ó The Author(s) 2020
Abstract In the cold gas spray process, deposition of particles takes place through intensive plastic deformation upon impact in a solid state at temperatures well below their melting point. The high particle impact velocities and corresponding peening effects can lead to high compressive residual stresses in cold spray coatings. This can be advantageous with regard to mechanical properties as fatigue life and hence, cold spray is an ideal process for repair applications. In this study, INCONEL 718 particles were cold sprayed by using nitrogen as propellant gas. The deposited coatings with different thicknesses were characterized using electron microscopy techniques to study grain refinement and precipitates in the coating. In addition, depth-resolved residual stress measurements have been performed by the incremental hole drilling method.
The residual stress depth profiles in the coatings indicate compressive residual stresses of several hundred MPa which are hardly influenced by the coating thickness. In addition, large compressive stress levels are found in surface-near regions of the substrate due to the grit blasting process. Furthermore, a post-heat treatment analysis was performed to investigate its influence on residual stresses and bonding strength. These findings are used to develop a consistent explanation of the dependence of strength values on thickness. Keywords Cold gas spraying Electron microscopy INCONEL 718 Incremental hole drilling method Residual stress
Introduction This article is part of a special topical focus in the Journal of Thermal Spray Technology on Advanced Residual Stress Analysis in Thermal Spray and Cold Spray Processes. This issue was organized by Dr. Vladimir Luzin, Australian Centre for Neutron Scattering; Dr. Seiji Kuroda, National Institute of Materials Science; Dr. Shuo Yin, Trinity College Dublin; and Dr. Andrew Ang, Swinburne University of Technology. & R. Vaßen [email protected] 1
IEK-1, Forschungszentrum Ju¨lich GmbH, 52425 Ju¨lich, Germany
2
Institut fu¨r Angewandte Materialien - Werkstoffkunde (IAMWK), Karlsruher Institut fu¨r Technologie, KIT-Campus Su¨d, 76131 Karlsruhe, Germany
3
Zentrum fu¨r Grenzfla¨chendominierte Ho¨chstleistungswerkstoffe (ZGH), Ruhr-Universita¨t Bochum, 44801 Bochum, Germany
4
Rolls-Royce Deutschland Ltd & Co KG., 15827 Blankenfelde-Mahlow, Germany
Cold gas spraying has become an important thermal spray process with numerous applications (Ref 1–3). A huge number of different materials reaching from pure metals to alloys and composites have been successfully deposited by this process reaching low porosity levels (Ref 4). The basic deposition mechanisms have been identified as a confined deformation, the so-called adiabatic shear instability, which leads to a re
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