IN718 Cold Gas Repair Spray of Large Cavities—Microstructure and Residual Stresses

Cold gas spray is an established process for coating substrates with similar or dissimilar materials. By use of a high-pressure process gas stream, solid particles are accelerated onto a substrate at supersonic velocities. The method is particularly suited for repair applications since neither structural changes nor oxidation occur during the process. To investigate the suitability of the cold gas spray process for the repair of major defects with up to 4 mm depth in Inconel 718 components, sample geometries were manufactured, containing tapered cavities. The specimen cavities were filled with Inconel 718 particles by a cold gas spray process. Non-destructive high-resolution neutron diffraction experiments were performed by use of the SALSA instrument at the Institut Laue-Langevin (ILL) to evaluate the local residual stress state in the as-sprayed condition. 2D maps of the residual stress distribution over the cross-sectional area of the filled cavities were determined. The results indicate compressive residual stresses within the filled process zone. Metallographic examinations show a good bonding between the repair filling and the substrate as well as strongly deformed particles within the repaired region. The latter indicates significant plastic deformation during cold gas spray, which is also in good agreement with increased diffraction line width from the neutron diffraction analyses in the filled process zone compared to the surrounding substrate.