Atomistic characterization of impact bonding in cold spray deposition of copper

We investigate the cold-spray additive manufacturing process of nanometric copper particles impacting a copper substrate using molecular dynamics (MD) and focus on the interplay between particle size (2–32 nm), particle velocity (100–2800 m/s), ensuing particle penetration depth and the impact bonding energy (IBE) binding the impinging particle with the substrate. It is observed, based on trends in the IBE, that even at low particle velocities (∼100 m/s) smaller sized particles (<8 nm) bind to the substrate, while there is a size-dependent critical velocity (≥200 m/s) for binding of larger particles (≥8 nm). At velocities near and above 500 m/s, material jetting and significant increase in particle penetration into the substrate are observed for larger particles. Rapid temperature increase, accompanied by adiabatic shear banding and instability (ASI), is observed, especially at the particle-substrate interface, resulting in particle-cratering at higher velocities in the range studied. Further, while jetting and ASI are observed together at high impact velocities, simulations show that ASI is not essential for jetting, consistent with recent investigations. In addition, both ASI and jetting are not prerequisites for particle binding to the substrate. A significant observation involves self-similar variations in particle penetration depth and IBE with particle kinetic energy across all particle sizes, which is captured by a quantitative constitutive relationship governing the particle's kinetic energy, penetration depth, and IBE.