Comparative Analysis of Microstructural and Mechanical Attributes in Low-Pressure Cold-Spray Coatings: Impact of Varied Cu Feedstock Powders

Abstract

In this study, the role of feedstock powder in influencing the characteristics of cold spray deposition is explored. Four distinct types of Cu feedstock powders, derived through electrolysis and employing varied gas atomization methods, are applied to a Cu substrate via low-pressure cold spray coating. We investigated the impact of feedstock powder on the resultant coatings' microstructure and mechanical properties. A comprehensive statistical model is developed, considering the cold spray parameters, weight change, coating thickness, and discerning their significance and interactions. Optimal conditions for carrier gas temperature and pressure are identified at approximately 400 °C and 1.99 MPa, respectively, consistent across all Cu powders. Velocity analysis reveals particle velocities ranging from 373 to 564 m/s under these optimal conditions. Coatings deposited using satellite-free gas-atomized powder, characterized by enhanced sphericity, exhibit superior characteristics, including minimal porosity (0.66 ± 0.35%), high flattening ratio (3.57 ± 1.51), elevated microhardness (107 ± 3 HV) and high bonding strength (20.7 ± 2.3 MPa). In contrast, coatings deposited with gas-atomized powder featuring microsatellite particles and electrolytic powder with irregular shapes display distinct properties. The observed trends are attributed to lower oxygen content and reduced oxide levels near the surface of the more spherical, satellite-free powder. This powder also demonstrates heightened plastic deformation during deposition. The increased peening effect of satellite-free gas-atomized powder during cold spray results in elevated dynamic recrystallization near the substrate surface, leading to smaller grains at the interface. Microstructural evolution analysis, utilizing electron backscatter diffraction, further elucidates the heterogeneous deformation and grain refinement occurring in Cu splats during cold spray coating.