The analysis of melting and refining process for in-flight particles in supersonic plasma spraying

摘要

To understand the effect of in-flight particle behavior so as to improve the coating quality, an accurate description of transport phenomena of particles is essential. For supersonic plasma spraying (SAPS), a three-dimensional computational model is developed to describe the plasma jet coupled with the injection of carrier gas and particles. The heating and melting processes of single particle were also studied by a numerical method. The model treats the particles in the flow as discrete Lagrangian entities that exchange mass, momentum, and energy with the gas. The governing equations for the Reynolds averaged flow parameters were solved using FVM method and the continuity and momentum equations are coupled using the PISO algorithm. The velocity and temperature of the in-flight particles were measured by SprayWatch-2i, and the morphology of particles was observed by Scanning Electron Microscope (SEM). Numerical and experimental results showed that, the velocity and temperature of the in-flight particles were reached maximum at the spraying distance of 80-100 mm. Particles were melted and broken into small child particles by plasma jet. The small child particles were accelerated to higher in-flight velocity by gas flow. Particles were completely melted when the spraying distance about of 95 mm at the time of 0.35 ms. Numerical results were compared with the experimental measurements and a good agreement has been achieved. (C) 2015 Elsevier B.V. All rights reserved.