Correlation of microstructure and properties of cold gas sprayed IN718

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 powder particles were cold-sprayed on Inconel 718 substrates by using nitrogen gas. The deposited coatings with different thicknesses were intensively characterized by SEM, EBSD and also TEM. Special focus was drawn on the grain refinement during spraying and the analysis of the precipitates in the coating. Depth sensitive stress measurements have been performed by the hole drilling method. The stress profiles in the coatings indicate compressive stress levels of several hundred MPa and are considerably influenced by the coating thickness. This will be discussed on the basis of the observed microstructural characterization. Finally, also tensile strength tests were performed which show a reduced strength with increased thickness. In a final discussion a correlation between microstructural results, stress profiles and strength data will be given.