Molecular Dynamics Simulation for Deposition and Bonding Mechanisms of Ti Particles upon Impact in Cold Spray

Molecular dynamics (MD) simulations have become an increasingly indispensable tool for investigating the atomic-scale mechanisms of the cold spray deposition process. Currently, copper (Cu) is frequently studied in MD-based cold spray investigations; studies have shown that titanium (Ti) and its alloys exhibit different deposition behaviors compared to Cu. Consequently, this study uses the MD simulation to investigate the deposition behavior within the Ti/Ti system. The results show that atomic intermixing occurs at the interface even at velocities below the critical velocity, with the intermixing region mainly localized in the central and annular zones near the edge. However, intermixing in the central region is diminished by particle rebound, resulting in weaker bonding in this region. As the particle and substrate deform, dislocations nucleate at the impact interface and propagate bidirectionally to the center of the particle. Analysis of the extreme values of normal and shear stresses reveals that differences of normal stress and shear stress in the Ti/Ti system are significantly higher than those of the Cu/Cu system, indicating that the deformation and bonding mechanisms of Ti particles are predominantly influenced by normal stresses. Furthermore, the interface microstructure indicates that interfacial amorphization due to the action of high normal stresses plays a significant role in the bonding process. Despite the significant discrepancy between the scale of the MD simulations and the real conditions, this study has significantly advanced our comprehension of the deposition and bonding mechanisms of Ti particles during cold spray.