04/06/22: Swetaparna and Carmine’s paper is published. Congrats!

In the cold spray additive manufacturing process, supersonic collisions of metal microparticles with stationary metal target substrates create highly inelastic events within tens of nanoseconds. The rapid mechanical interactions, particularly at the microparticle-substrate interface, produce adiabatic plastic deformation, eventually enabling solid-state consolidation. Since the extreme mechanical processes are inherently nonlinear and are significantly influenced by the materials’ conditions at the contact interface, controlled studies of impact and bonding dynamics of these microparticles help to better understand the solid-state consolidation mechanism. In this study, the extreme dynamic behavior of aluminum 606l alloy microparticles (~ 20 µm diameter) impacting the aluminum 6061 alloy substrate as a model system is systematically investigated using the laser-induced projectile impact test. The controlling parameters of these experiments are impact velocity (50-1,000 m/s) and substrate oxide film thickness (10 and 20 nm additional oxide layers prepared by atomic layer deposition). The influence of the substrate oxide layer on the dynamic responses of the microparticles is quantified as a semi-empirical function involving two characteristic transition points. Moreover, cross-sectional electron microscopy reveals that thickness-dependent fracture characteristics of the oxide layers support the origins of the transitional dynamics. Since the presence of a nanometer-thick oxide layer on a target substrate is realistically unavoidable, this controlled experimental study will enrich the understanding of the bonding dynamics influenced by the oxide layer in cold spray.