THERMAL BARRIER COATINGS ON TURBINE-BLADES BY PLASMA SPRAYING WITH IMPROVED COOLING

Turbine blades were coated with a thermal barrier coating system consisting of an MCrAlY bond coat about 100 mu m thick deposited by Lo Ic-Pressure Plasma Spraying (LPPS) and a 300 mu m thick ZrO2-7 wt. % Y2O3 top coat. The latter was manufactured by both Atmosphere and Temperature Controlled Spraying (A TCS) and Air Plasma Spraying (APS) using internal air cooling through the cooling holes of the turbine blades. Coated blades were submitted to thermal cycling tests in a burner rig with hot gas temperature of 1485 degrees C. In the case of ATCS coated blades the number of cycles until the first spallation al the leading edge of the blade was between 350 and 2400. The number of cycles of the thermal barrier coatings sprayed with internal cooling was between 1200 and 1800. Furnace cycling tests were also carried out with ATCS coated blades at temperatures of 1100 and 1200 degrees C. The results of thermal cycle tests and the investigations of the microstructure are discussed.