Three-dimensional simulation of thermal plasma spraying of partially molten ceramic agglomerates

Thermal plasma spraying of agglomerated nanostructured ceramic particles has been studied using computational fluid dynamics. The plasma jet is modeled as a mixture of Ar-H-2 plasmas issuing into a quiescent atmosphere. The particles, modeled as micron sized spheres, are introduced into the jet outside the plasma gun exit with radial injection. The existence of a simple target in front of the plasma gun is taken into account. The trajectories and state histories of particles of various sizes during their flight through the jet are presented. Moreover, the solid-liquid interface within the particles is tracked in an attempt to predict the amount of unmelted material retained in these particles at various axial distances from the gun exit. The effects of turbulence in the jet on these particle histories are accounted for. It is shown that, for the range of particle sizes and the plasma gun operating conditions studied, both the deposition location and the retained unmolten fraction are strongly affected by the size of the particles. The predictions are significant in terms of showing general trends, which will be useful in identifying processing windows for producing optimally nanostructured coatings.