A Plasma Torch Designed for Low Pressure Plasma Spraying and Formation of Yttria Stabilized Zirconia Coatings

Abstract This study investigates the spraying characteristics of low-pressure plasma torches with different nozzle sizes. YSZ feedstock powders were sprayed with each torch at different stand-off distances and gas pressures. The plasma jets created were photographed and measured, showing that low-pressure spraying significantly increases plume length and diameter compared to atmospheric conditions. The coatings obtained were examined and microhardness was determined. It was found that the longer nozzle increases the temperature of the plasma jet, and with a longer dwell time, the particles heat more efficiently and evaporate more fully. At a spraying distance of 300 mm, the coatings were mostly composed of equiaxed grains, which were much larger in the coatings produced with the long anode nozzle. At longer spraying distances, more unmelted particles appeared in the coatings, leading to a reduction in hardness.