Highly Porous Thick Thermal Barrier Coatings Produced by Air Plasma Spraying of a Plastic-Ceramic Mixed Powder

In order to increase the efficiency of heavy duty gas turbines for power generation and to reduce their emissions, higher combustion chamber temperature is required; a considerable improvement of the insulation properties of the thermal barrier coatings is therefore required. 1.5 mm thick thermal barrier coatings have been deposited by air plasma spraying a mixed polyester-zirconia powder; by this process high porosity, up to 22%, has been achieved together with a good deposition efficiency (about 50%); the coating microstructure has been thoroughly examined by quantitative image analysis, determining the pores size distribution and the vertical segmentation cracks density. Thermal shock tests showed a life improvement with respect to the state-of-art by a factor > 100; relationships among thermal shock life, deposition rate, segmentation cracks density and porosity were determined. Thermal expansion and thermal diffusivity were measured up to 1200 °C; failure strength, failure strain and Young's modulus were determined by a four-point bending technique.