Effect of (Thermo-) Mechanical Post-Treatments on Material Properties of Cold-Sprayed Inconel®625 Coatings
摘要
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. Hence, further process optimization and/or post-treatments are needed to reach deposit qualities with low porosity and sufficient strength. In this study, two (thermo-) mechanical post-treatments are used for modification of deposit properties; Laser Shock Peening (LSP) to close internal porosities and to heal out non-bonded interfaces by induced compressive shock waves and Surface Rolling (SR) for further deposit densification, work hardening and surface smoothing. These treatments are associated with compressive residual stresses. Compressive residual stresses, resulting using LSP as post-treatment reached to − 540 MPa in 0.15 mm and − 450 MPa in 0.10 mm depth underneath the top surface for deposits produced with small η = 0.95 and high η = 1.11 correspondingly. 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, LSP reduces deposit porosities by 37% and 34%, respectively. The results demonstrate that Surface Rolling can be used to decrease porosities from 0.16% in as-sprayed condition to 0.01% after SR. Surface Rolling the deposits reduced their surface roughness by up to 95% (from Rz = 31.28 µm to Rz = 1.45 µm) and increased the microhardness by about 4%. The obtained benefits of SR are mainly due to the severe deformation and build-up of compressive residual stresses within a depth of up to 200 µm beneath the top surface. In summary, LSP proves to be an effective tool to further enhance the quality of Inconel®625 cold-sprayed deposits and in view of applications, Surface Rolling can be used to tailor deposit qualities, as well.