Microstructure and Thermal Conductivity of Thermal Barrier Coatings Processed by Plasma Spray and Physical Vapor Deposition Techniques

Abstract

AbstractThe temperature dependence of the thermal conductivity of multilayer coatings made by a plasma spray technique as well as some coatings made by physical vapor deposition (PVD) was investigated. The multilayer coatings consisted of a varying number of layers of Al2O3 and ZrO2 stabilized by 8%Y2O3. Plasma sprayed coatings exhibited a large reduction in thermal conductivity at all temperatures when compared to the bulk monolithic materials. This reduction was found to be due to porosity as well as thermal resistance brought about by interfaces in the coatings. A comparable reduction in thermal conductivity was achieved in monolithic ZrO2 as well as in a composite coating deposited by the PVD technique. Microstructural factors that may be responsible for this reduction are discussed.