Deposition and Testing of Thermal Barrier Coatings on Gas Turbine Vanes

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 150 μm thick layer of NiCoCrAlY as a bond coat and a 300 μm 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.