Deformation of copper particles upon impact: A molecular dynamics study of cold spray

In this work, Molecular Dynamics simulations were performed to predict and provide detailed understanding of the deformation behavior of solid copper particles accelerated against a copper substrate. Simulations were carried out at an initial particle/substrate temperature of 300 K. The particles were assigned an initial velocity of 1000 m/s normal to the substrate surface, oriented in the [1 1 1] direction. The particles diameter was varied from 5 to 40 nm in order to assess changes in the deformation behavior due to size effects. For particles with diameters larger than 10 nm, the results showed well-defined patterns of dislocation activity associated with three distinct stages of deformation. The onset of plastic strain was localized at the flattened particles bottom, in the region of contact with the substrate, and characterized by the heterogeneous nucleation of Shockley partial dislocations. In the subsequent stage, a dense dislocation network was formed in the lower half of the particles, while the top of the particles remained undeformed. The plastic deformation of the top of the particles completed the process, resulting in the final flattened splat shape. High temperatures (above 1000 K) were observed at the particle-substrate interface, where fluid-like flow contributed to the formation of material jetting.