Process Conditions and Microstructures of Ceramic Coatings by Gas Phase Deposition Based on Plasma Spraying

Plasma spraying at very low pressure (100 - 200 Pa) is characterized by particular plasma conditions being significantly dissimilar from atmospheric conditions. Applying powderous feedstock it is possible to defragment the particles into very small clusters or even to evaporate the material. As a consequence, the deposition mechanisms and the resulting coating microstructures are fundamentally different when compared to conventional liquid splat deposition. Thin and dense ceramic coatings can be achieved as well as columnar structured strain tolerant coatings with low thermal conductivity offering new possibilities for application in energy systems.

To exploit the potential of such gas phase deposition from plasma spray based processes, the deposition mechanisms and their dependency on process conditions must be understood. Thus, plasma conditions were investigated by optical emission spectroscopy. Coating experiments were performed at varied process parameters. Based on the observed microstructures, a phenomenological model is developed to suggest basic deposition mechanisms.