37. Materials Aspects of Thermal Barrier Coatings

Thermal barrier coatings (TBCs) are being used for the past few decades for providing thermal insulation to metallic components of hot parts of gas turbine engines. The low thermal conductivity ceramic coatings contribute toward maintaining a large temperature difference between the hot gases in the gas turbine and the superalloy components. High engine efficiency as well as prolonged component lifetime can be achieved by integrating TBCs with gas turbine components at the design stage itself. While yttria-stabilized zirconia emerged as the work-horse TBC material, a few other advanced compositions are also being used by some of the engine manufacturers. Prominent among these are zirconia-based compositions with rare-earth oxide additions, either with tetragonal or pyrochlore structure. A lot of research activity has focused on durability issues relevant to the TBC technology, for enhancing reliability as well as performance. Phase transformations, oxidation-induced residual stress, changes in fracture toughness, and thermochemical attack by contaminants ingested by the engine are some of the important degradation mechanisms governing durability.