Peening Effects at Low Particle Impact Velocities on Properties of Cold Sprayed Aluminum Coatings

During material deposition by cold spraying, in situ shot peening or non-bonding particles by enhanced plastic deformation can contribute to coating densification and improved coating properties. To systematically investigate the influence of overall applied strain, the research in the present study on pure aluminum investigates peening effects over a wide range of spray parameter sets in the low-velocity regime. Key data, including deposition efficiency, coating strength, microstructure, porosity, hardness, and internal flattening, were evaluated. The results showed that deposition at low particle velocities and, thus, low deposition efficiencies result in negligible porosity and high deposit strengths, which even exceed those obtained at high impact velocities. In agreement with the low deposition efficiencies, the study of single-pass surface coverage by wipe tests revealed that particle bonding only rarely occurred at low velocities. This confirms that the embedding and strengthening by peening effects of subsequent rebound particles contribute to conditions that ensure bonding at internal interfaces. Sufficiently high strains could break surface oxides and allow for metallic bonding across the interface. This finding not only enables the improvement of coating properties but also promotes the understanding of the bonding behavior at low particle velocities.