PLASMA SPRAY-PHYSICAL VAPOR DEPOSITION (PS-PVD) OF CERAMICS FOR PROTECTIVE COATINGS

摘要

In order to generate advanced multilayer thermal and environmental protection systems, a new deposition process is needed to bridge the gap between conventional plasma spray, which produces relatively thick coatings on the order of 125-250 microns, and conventional vapor phase processes such as electron beam physical vapor deposition (EB-PVD) which are limited by relatively slow deposition rates, high investment costs, and coating material vapor pressure requirements. The use of Plasma Spray - Physical Vapor Deposition (PS-PVD) processing fills this gap and allows thin (< 10 m) single layers to be deposited and multilayer coatings of less than 100 m to be generated with the flexibility to tailor microstructures by changing processing conditions. A PS-PVD processing facility has been recently built at the NASA Glenn Research Center and is being applied to the development of advanced coatings for turbine engine hot section components. To develop a basis for understanding the range of processing parameters and the effect on coating microstructure for this new processing capability at NASA GRC, a design-of-experiments was used to deposit coatings of yttria-stabilized zirconia (YSZ) onto NiCrAlY bond coated superalloy substrates to examine the effects of process variables (Ar/He plasma gas ratio, the total plasma gas flow, and the torch current) on chamber pressure and torch power. Coating thickness, phase and microstructure were evaluated for each set of deposition conditions. Low chamber pressures and high power were shown to increase coating thickness and create columnar-like structures. Likewise, high chamber pressures and low power had lower deposition rates, but resulted in flatter, more homogeneous thicknesses. The trends identified in this study are being used to improve coating processing control and to guide parameters for tailoring the microstructure of advanced coatings.