An experimental/numerical study of bonding mechanism in cold spray technology for metals

The cold spray technology is a relatively new additive process allowing for the deposition of metallic coatings on metallic substrates; the particles impacting on target surface at high velocity deform and bond together leading to the coating formation and grow-up. Although the impact phenomena have been studied by several scientists in the last decades, the actual bonding mechanism for cold spray particles is still a recent focus of research. Therefore, aiming to further investigate the intriguing phenomena governing the particle-substrate interaction in cold spray, both experimental and numerical studies were carried out in this research activity. Ballistic tests were performed by impacting a single lead particle (1.5 mm in diameter) on a lead substrate at different impact velocities through a light ballistic airgun. A high-frequency camera was used to observe the particle impact and measure impact and rebound velocities. A detailed 3D quarter symmetric numerical model was developed and impact simulations were performed. The comparison between the experimental results and the numerical outcomes in terms of particles and substrate deformations as well as particle rebound velocity allowed for the validation of the model. The validated numerical approach was used to study the thermo-mechanical regimes taking place on impact surface pointing out the rule of strain-temperature interaction in cold spray bonding. On these results, a temperature-based bonding hypothesis was proposed and an original bonding algorithm was implemented on the numerical model.