This paper discusses the development of a two-layer thermal barrier coating that reduces heat flow to the lowest allowable level based on the temperature limits of the materials involved. The thick, porous coating was sprayed using a modified plasma torch and then thermally cycled until failure. Test results show that the process used to apply the bond coat has a measurable effect on the performance of the thermal barrier coatings. In addition to zirconia powders, a low cost polymer powder was used as well. Paper includes a German-language abstract.

HVOF spraying is used to produce NiCoCrAlYRe deposits that serve as adhesive layers for plasma-sprayed thermal barrier coatings. This paper investigates the influence of HVOF spray parameters on the structure and properties of the adhesion-promoting layers. Spray parameters are optimized to produce high layer densities with low degrees of oxidation and a surface roughness comparable to that of the thermal barrier coatings. A vacuum-sprayed layer with similar composition is also examined. Following the application of the TBC, the oxidized layers are characterized based on microstructure, oxide layer thickness, proportion of the NiAl phase, and imperfections at the boundary layer. It is observed that the less expensive HVOF layer offers the same protective properties as a vacuum plasma sprayed bond coat. Paper includes a German-language abstract.

An innovative methodology to deposit, by plasma spraying, ceramic thermal barrier coatings on gas turbine blades and vanes was developed. Such a methodology produces a pattern of microcracks in the coating, thus improving its thermal shock resistance. After a laboratory campaign of process optimization and coating characterization, real components were coated with a 150µm thick layer of NiCoCrAlY as a bond coat and a 300µm thick layer of ZrO2, partially stabilised with 8%of Y2O3, as a top coat. In particular, four vanes, taken from the first stage of a land based gas turbine (V64.3, produced by Ansaldo), were coated on the whole airfoil. The four vanes were submitted to a cyclic oxidation test in a burner rig simulating the operative conditions of a gas turbine. In particular, they were exposed to a gas flow with the same composition, temperature and speed of the inlet gas of a real gas turbine; moreover, they were cooled by an internal stream of compressed air for obtaining the same temperature profile of a vane in operation. The surface temperature of the vanes was monitored during the test by an optical pyrometer and the internal temperature by a thermocouple. After 550 hours of test, corresponding to 550 cycles, the four vanes did not show any sign of damage.