Abstract
Thermal barrier coatings (TBCs) are capable of protecting hot-section engine components from the hot gas stream, and thereby can provide improvements in component durability and engine efficiency. Thick TBCs can provide further improvements in durability and efficiency, especially for static components. The main commercial coating methods for TBCs are electron beam physical vapor deposition (EB-PVD) and air plasma spray (APS). These processes have limitations for depositing thick TBCs: for EB-PVD, the deposition rates are low and the cost is high; for APS, durability is reduced with increased thickness. Inframat Corporation, in collaboration with the University of Connecticut, is developing a new plasma spray process, namely, solution precursor plasma spray (SPPS), for the formation of TBCs and also functional films from liquid precursor feedstock, instead of the solid powder feedstock used in conventional APS. SPPS TBCs have many unique microstructural features, including: ultra-fine splats, vertical micro- and macrocracks, micrometer- and nanometer-size porosity. These unique microstructural features provide a TBC with high thermal cycling spallation life and bond strength. These coatings have been made in thickness up to 2 mm and show excellent durability. In this paper we present microstructural characteristics and thermal cycling performance of SPPS-formed 7YSZ thick coatings varying in the range of 0.5-2 mm.
