Deposition and Bonding Mechanism of Multiparticle Impacts in Cold Spraying: A Molecular Dynamics Simulation.

Subsequent particle impacts during cold spraying significantly influence the deformation and bonding characteristics of previously deposited particles. Due to the small particle size and extremely short deposition duration, experimental investigation of this phenomenon remains challenging. In contrast, numerical simulation offers a feasible approach to capturing minute material changes occurring over extremely brief time intervals. Molecular dynamics (MD) simulation can effectively reproduce the dynamic deformation behavior of materials at the atomic scale under extreme processing conditions and has become an essential tool for analyzing particle deformation and structural evolution during cold spraying. In this study, titanium (Ti) was selected as the spraying material, and an MD-based multiparticle impact model was developed to investigate the deformation and structural evolution of underlying particles subjected to sequential impingement. Furthermore, the synergistic effect of the particle velocity in enhancing this influence was systematically examined. The results demonstrate that under the impact of subsequent particles the bottommost particles undergo continuous deformation in the X, Y, and Z directions, inducing progressive deformation in the substrate. Concurrently, significant atomic intermixing is observed between the bottommost layer and the substrate as well as between the first- and second-layer particles. Stress evolution reveals that repeated impacts lead to continuous stress accumulation in the bottom region, with stress values exhibiting a sustained upward trend, which drives the internal crystal structure to transform into an amorphous phase, and higher particle velocities further accelerate amorphization. Furthermore, dislocations nucleate within high-stress regions and propagate inward progressively. Overall, these findings indicate that successive particle impacts enhance bottom-layer deformation through persistent stress transmission, promoting dislocation generation and structural amorphization, although this effect is gradually attenuated when the fourth layer is deposited. Despite inherent scale limitations in MD simulations compared to real conditions, the results provide valuable insights into the cold spray deposition mechanisms of difficult-to-deform metals.