Recent Developments on Al₂O₃-Based Thermal Barrier Coatings

The rising demand for increasing the operating temperature of gas turbine engines has generated many technological inventions. With the high-performance expectation of gas turbine engines for an economical and environmental aspect, researchers focus on the development of materials which can tolerate high temperatures, high stress, and the evolution of ceramic coatings. In this respect, thermal barrier coatings (TBC) play a major role in protecting hot sections of modern gas turbine systems. Yttria-stabilized zirconia (YSZ) is widely used commercially on metal superalloy parts to provide insulation for high temperatures. However, some disadvantages of YSZ such as high-temperature phase transformation (~1200 °C) and high oxygen ions permeability enable researchers to search for alternative thermal barrier coatings materials and designs. One of the TBC materials alumina (Al₂O₃) is not viable alone for TBC top coat because of its low coefficient of thermal elongation compared with bond coat and substrate. However, Al₂O₃ coating together with other TBC materials on the metal substrate using different methods and designs can improve the mechanical and thermal properties of TBC while providing better protection to the metal substrate from oxidation. This chapter discusses the Al₂O₃-based TBC systems, the production of different complex designs, laser surface modification, comparison with YSZ and ceria-yttria-stabilized zirconia (CYSZ), and testing methodology.