Shot Peening for Improving Surface Integrity and Corrosion Resistance of DMLS-Fabricated Cu–Ni Alloys

Surface defects inherent to Direct Metal Laser Sintering (DMLS) can significantly degrade the corrosion resistance of Cu–Ni alloys in chloride-containing environments. This study investigates the combined influence of DMLS processing parameters (laser scan speed and layer thickness) and shot peening (SP) post-treatment on the surface integrity and corrosion behaviour of additively manufactured Cu–Ni alloys. Porosity, surface roughness, microhardness, residual stress, and corrosion rate were characterised using optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The results show that increasing layer thickness and scan speed leads to higher porosity, greater surface roughness, and reduced hardness in the as-built condition, resulting in poorer corrosion performance. Specimens fabricated with a finer layer thickness (20 μm) exhibited substantially lower corrosion rates than those produced with thicker layers (60 μm), confirming the strong influence of DMLS processing parameters on corrosion behaviour. Shot peening significantly improved surface integrity by reducing surface defects and introducing compressive residual stresses, which enhanced corrosion resistance. The corrosion rate decreased by up to 77%, from 0.67 mm/y in the as-built condition to 0.15 mm/y after shot peening. Among the investigated conditions, specimens fabricated with 20 μm layer thickness and 100 mm/s scan speed followed by shot peening exhibited the most favourable combination of properties, including the lowest corrosion rate and improved surface integrity. These findings demonstrate that shot peening is an effective post-processing technique for improving the durability of DMLS-fabricated Cu–Ni alloys for marine and chemically aggressive applications.