Numerical Study of Gas and Particle Flows in Vacuum Cold Spray Process: Effect of Standoff Distance

Vacuum cold spray is an emerging coating process which has been used for ceramic deposition with applications in industries such as MEMS, fuel cells, optical devices and RF components. During deposition, various parameters play influential roles such as nozzle geometry, powder size and material, pressure inside the deposition chamber and carrier gas pressure. This work is focused on the effect of nozzle geometry and substrate location on the gas flow and particle velocity, temperature and trajectory. Numerical study is performed using a two-way coupled Eulrian-Lagrangian model for different nozzle geometries with various pressure ranges and standoff distances. Locations of the predicted shocks for the free jet case are validated against the theoretical and experimental studies in the literature. By placing a substrate in the computational domain at various standoff distances, the characteristics of gas flow, bow shock and importantly particle trajectories and conditions upon impact have been examined. Accordingly, the optimized standoff distance based on maximizing particle impact velocity is determined.