Dynamic modeling of micro- and nano-sized particles impinging on the substrate during suspension plasma spraying

Suspension plasma spraying (SPS) can be utilized to manufacture finely structured coatings. In this process, liquid suspended with micro- or nano-sized solid particles is injected into a plasma jet. It involves droplet injection, solvent evaporation, and discharge, acceleration, heating, and melting of the solid particles. The high-speed and high-temperature particles finally impact on the substrate wall, to form a thin layer coating. In this study, a comprehensive numerical model was developed to simulate the dynamic behaviors of the suspension droplets and the solid particles, as well as the interactions between them and the plasma gas. The plasma gas was treated as compressible, multi-component, turbulent jet flow, using Navier-Stokes equations solved by the Eulerian method. The droplets and solid particles were treated as discrete Lagrangian entities, being tracked through the spray process. The drag force, Saffman lift force, and Brownian force were taken into account for the aerodynamic drag force, aerodynamic lift force, and random fluctuation force imposed on the particles. Spatial distributions of the micro- and nano-sized particles are given in this paper and their motion histories were observed. The key parameters of spray distribution, including particle size and axial spray distance, were also analyzed. The critical size of particle that follows well with the plasma jet was deduced for the specified operating conditions. Results show that in the downstream, the substrate influences the flow field structure and the particle characteristics. The appropriate spray distances were obtained for different micro- and nano-sized particles.