Modification of Cold Sprayed Inconel®625 Deposits by Laser Shock Peening

Cold spraying of high strength materials, i.e., Inconel®625, is challenging due to restricted deformability and thus high critical velocity to achieve bonding. This affects the reachable extent of well-bonded areas and therefore tensile strength. In this study, Laser Shock Peening (LSP) is used as post-treatment to close internal porosities and to heal out non-bonded interfaces by induced compressive shock waves. The laser treatment was performed using a Q-switched Nd: YAG laser operating at 10 Hz frequency with a pulse duration of 10 ns. The maximum values of compressive residual stress were determined to be -450 MPa in 0.1 mm and -540 MPa in 0.15 mm depth underneath the top surface for deposits with high- and low-quality deposits (with small η=0.95 and high η=1.11 respectively). The induced compressive stresses decrease with increasing distance to surface and reach a depth of up to 300 µm. For deposits processed with high- and low-η values as high-quality and low-quality deposits and different porosities, the results indicate that Laser Shock Peening reduces deposit porosities by 37 % and 34 % as well as overall thickness of initially 2 mm by 23 µm and 34 µm, respectively. This can be explained by induced plastic deformation and compressive residual stresses. Thus, LSP proves to be an effective tool to further enhance the quality of cold spray deposits.