Due to its high chromium content, Inconel®625 is often used as protective coating to withstand corrosion in harsh environments. So far, Inconel®625 coatings are typically applied by thermal process routes such as deposition welding or thermal spraying. In order to prevent the oxidation associated with the thermal process routes, solid state deposition by cold spraying (CS) could offer advantages for building up the needed layers in a thickness range from about 0.2 to several millimetres. However, cold spraying of nickel-based superalloys like Inconel®625 is still challenging due to their high strength and respective high critical velocities for successful deposition. Previous studies investigated the optimization of cold spray parameter sets to improve the ratio ɳ between particle impact velocity and material’s critical velocity [1] and proved that increased coating quality parameters ɳ ensure better deposit properties.

The present study now deals with influences of robot kinematics and associated surface temperatures to reduce porosity and to improve cohesive strength. Inconel®625 powder was cold sprayed on structural carbon steel substrates using N2 as propellant gas under various stand-off distances (SoD) and travers gun speeds (Vtrav.). The quality of as-sprayed Inconel®625 thick deposit was characterized in terms of micro¬structure, porosity, electrical conductivity, hardness, cohesive strength and residual stress. The results demonstrate that deposit quality can be improved by decreasing the SoD and Vtrav., leading to a low coating porosity of less than 1 % and higher cohesive strength (UTS). In addition, the usually compressive stresses of cold sprayed coatings by peening effects are also reduced at lower SoD and Vtrav. This can be attributed to superimposed tensile stresses by higher surface temperatures. In summary, the secondary parameters given by kinematics during the deposition can be systematically tuned for further optimization of deposit properties.

[1] F. Taherkhani et al., Cold spraying of Inconel®625 thick deposits, International Thermal Spray Conference (ITSC2023), May 22-25, 2023, Quebec City, Canada, 7 pages.