Suspension Spray for Thermal Barrier Coatings - Expanding the Envelope

Suspension plasma spray for thermal barrier coatings has become an industrially accepted coating method in recent years. The aerospace certification of suspensions demonstrates the advances that have been made since the technique was first developed. While the first coating are entering service, further development of the process is needed to expand is use within the gas turbine. High solids load suspensions have been used to produce TBC coatings at spray rates comparable to powder spraying; it has yet to be demonstrated that these coatings improve upon the properties of standard suspension coatings. This study has focused on the comparison between an industry standard suspension used for production with higher solids load suspensions formulated using ethanol and aqueous based solvents. The coating process has been customized for each suspension to obtain a coating with the required columnar or highly segmented structure. The coating processes have been compared in terms of spray rate and deposition efficiency to assess their impact on production. The coatings produced from each suspension have been characterized for their properties in terms of thermo-cyclic fatigue lifetime. The thermal conductivity of the coatings has been measured in their as produced state as well as after exposure to high temperatures.