Abstract

Thermal spray technology is a widely used technique in industry in which surfaces of materials are coated by spraying a wide range of metals or ceramics. Considering the growing interest in building nanostructured coatings due to their significant characteristics a new technique called suspension plasma spraying is developed. In this method, a coating is formed by injecting a suspension of nano or sub-micron sized particles into a plasma flame. Obtaining a uniform coating on mechanical parts is one of the industrial challenges in suspension plasma spraying. Through a three dimensional numerical analysis, this study is aimed at providing a better understanding of the effect of substrate position and curvature on in-flight particle temperature, velocity and trajectory. The high temperature and high velocity plasma flow is simulated inside the plasma torch using a uniform volumetric heat source in the energy equation. The suspension of yttria stabilized zirconia (YSZ) particles is used here due to its vast applications in forming thermal barrier coatings. Suspension is molded in this study as a multicomponent droplet while catastrophic breakup regime is considered for simulating the secondary break-up when the suspension interacts with the plasma flow. A two-way coupled Eulerian-Lagrangian approach along with a stochastic discrete model was used to track the particle trajectory. Particle size distribution in the vicinity of the substrate at different standoff distances has been investigated. Then the effect of substrate curvature on in-flight particle characteristics is discussed. The results show that sub-micron particles obtain higher velocity and temperature compared to the larger particles. However, due to the small Stokes number associated with sub-micron particles, they are more sensitive to the change of the gas flow streamlines in the vicinity of the substrate.