Cold gas spraying (CGS), a solid-state material deposition technique, is highly suitable for depositing temperature- and oxidation-sensitive materials [1]. The current study is part of the collaborative project CORE (Computerized Refurbishment), funded by dtec.bw and the European Union – NextGenerationEU, which aims to utilize CGS as an advanced repair technique for aerospace applications [2]. The residual stresses (RS) induced by CGS play a crucial role in the performance and mechanical integrity of CGS-repaired parts. Local plastic deformation caused by high-velocity particle impacts and local heat input are the primary contributors to RS build-up in CGS. The present study investigates the influence of process parameters and substrate geometry on the RS distributions generated by CGS. Moreover, adhesion between the deposited material and the substrate is characterized by load transfer across the interface during 4-point bending of samples with cavities filled by CGS.
Different material combinations were examined, including Al6061 deposited on Al6061, and grade 1 titanium (Ti) deposited on Al6061 and grade 2 titanium (Ti) substrates, using different substrate geometries such as sheet metals, square hollow section tubes, and milled cavities. The experimental investigation of RS distributions on the sheet metals and the square hollow section tubes was carried out using the incremental hole-drilling method complemented by X-ray diffraction stress analysis. The adhesion between the deposits and the substrates was analyzed by in situ energy-dispersive X-ray diffraction (EDXRD) using high-energy synchrotron X-radiation during 4-point bending carried out for bending bars with cavities filled by CGS. Here, the load transfer is determined by lattice strain scanning across the interface.
The peening effect in CGS, arising from high-velocity impacts of solid particles, is widely known to induce compressive RS. However, the results indicate that depending on the materials and process parameters, this compressive RS may be superimposed or even dominated by tensile RS (Figure 1b; grade 1 Ti deposited on grade 2 Ti with varied nozzle scanning speeds). Those are generated by the localized “quenching effect” associated with local heat input and thermal gradients during progressive material deposition, as well as by the stresses arising from the thermal property mismatch between deposited and substrate materials (Figure 1c; grade 1 Ti deposited on Al6061).