Abstract
The morphology and chemistry of low pressure plasma sprayed (LPPS) yttria coatings was investigated. White yttria powder used as the coating source material was 99.99% pure and contained particles from 1 to 5 microns in size. This yttria powder was plasma sprayed onto 8.9 cm diameter, 0.635 cm thick aluminum substrates using Ar-He as the arc gas. The powder gas was varied from Ar, to air to O2 between samples. The sample sprayed using Ar as the powder gas used a chamber pressure of 2.5 kPa and resulted in a very dark colored coating. Subsequent samples were sprayed using air and then oxygen as the powder gas, both using a chamber pressure of 4.0 kPa. The resulting coating colors were medium gray and very light gray, respectively. A duplicate spraying using oxygen as the powder gas was performed to demonstrate repeatability. Porosity, splat shape, and the presence of amorphous phases were determined using secondary and backscattered electron microscopy imaging and related to processing conditions. Energy dispersive spectrometry was used to examine the chemistry of the coating and substrate. X-ray photoelectron spectroscopy (XPS) was used to determine the oxide stoichiometry of each of the coatings and this was correlated to coating color.
