Insight into the residual stress build-up for cold gas spraying of metallic coatings

Cold gas spraying (CGS) being a solid-state material deposition technique is highly suitable for the deposition of temperature and oxidation sensitive materials. The current study is a part of the collaborative project CORE (Computerized Refurbishment) funded by dtec.bw, European Union - NextGenerationEU aiming to utilize CGS as an advanced repair technique for aerospace applications. The residual stresses (RS) build-up in CGS play a crucial role in the performance and mechanical integrity of CGS-repaired parts. The current work focuses on a systematic study on the influence of CGS parameters on RS build-up and understanding the progressive stress development during CGS deposition of titanium coatings on different substrate materials by means of in-situ curvature based RS analysis using an in-situ coating property (ICP) sensor. Furthermore, the post-spraying analysis of the final RS distributions was carried out by means of the incremental hole-drilling method and by X-ray diffraction. The results suggest that the RS in CGS deposited components are primarily influenced by local heat input, local temperature distributions and geometrical boundary conditions. In CGS, the peening effect caused by high velocity impacts of solid particles leading to compressive RS is widely known. However, these compressive RS contributions are superimposed or even dominated by tensile RS resulting from local temperature distributions and thermal property mismatch between deposited and substrate materials.