Generic correlation of spray distance with in-flight particle behavior for different kinds of materials in air plasma spraying

This paper investigates the influence of spray distance on inflight particle status for Yttria Stabilized Zirconia (YSZ), Mo and NiCrAlY thermal spray powders in Ar-H₂ plasma through modeling and experiments. Distributions of individual particle characteristics such as temperature, velocity and size at the point of the maximum particle flux and points of the squared grids were measured for a few plume cross-sections. Numerical simulations were performed using the experimental conditions, and parametric studies were also performed. In-flight particle characteristics and their distributions were presented at different standoff/spray distances to reveal the heating and melting behaviors of different kinds of materials such as metal, alloy and ceramics powders. It can be found that for ceramic, metal and alloy powders, the particle velocity and temperature all increase with spray distance and then decrease after reaching maximum. However the positions of maximum temperature and velocity depend strongly on the material and size of the particles. The statistical distributions of temperature and velocity at different spray distances were also presented. It can be observed that the temperature distribution becomes narrower as spray distance increases. The occurrence of such behavior can be explained by analyzing particle kinetic energy and molten status. The correlations between powder properties and spray conditions have been established and they can serve as guidance for spray distance optimization of air plasma spraying for metal, alloys and ceramics particles.