A ceramic coating of low thermal conductivity applied to the surface of high-temperature components. It consists of a zirconia top coat and a bond coat, and greatly lowers the metal temperature.
Japanese name: 遮熱コーティング
Thermal barrier coating appears in 3 practice questions across 1 topic, including High-temperature materials and creep.
Answer: A. Beneath a low-conductivity zirconia (YSZ) top coat lies a bond coat such as MCrAlY, and a thin Al₂O₃ thermally grown oxide (TGO) forming at their interface protects the substrate from oxidation
A TBC is a coating that lowers the metal temperature with an insulating surface layer while the inside of the blade is cooled by cooling air. The YSZ (yttria partially stabilized zirconia) top coat has a low thermal conductivity of about 1 to 2 W/(m·K) and, for a ceramic, a large thermal expansion coefficient. It is made as a porous sprayed coating or a columnar vapor-deposited coating to relieve the strain from the thermal expansion mismatch with the substrate. YSZ conducts oxide ions well and cannot stop oxygen, so Al in the bond coat oxidizes to form a thin Al₂O₃ TGO, which protects the substrate from oxidation. When the TGO thickens or undergoes thermal cycling, the top coat spalls from near it, which is the main factor limiting the life. A material with high thermal conductivity cannot serve as insulation.
Answer: C. About 208 K
From Fourier's law q = kΔT/L, ΔT = qL/k = (1.0×10⁶ × 250×10⁻⁶)/1.2 ≈ 208 K. That a coating only about 0.25 mm thick can lower the metal temperature by about 200 K is the benefit of a thermal barrier coating. The creep strength of nickel-based superalloys is sensitive to temperature, so this temperature difference strongly affects the life and the allowable gas temperature. About 300 K multiplies by the thermal conductivity instead of dividing, and about 21 K converts the thickness as 25 µm, an order of magnitude too small. The lower the thermal conductivity and the thicker the coating, the larger the temperature difference, but thicker coatings spall more easily under thermal stress, so the thickness is limited.
A TBC is a coating that lowers the metal temperature with an insulating surface layer while the inside of the blade is cooled by cooling air.
Which statement about the structure of a thermal barrier co…That a coating only about 0.25 mm thick can lower the metal temperature by about 200 K is the benefit of a thermal barrier coating.
A heat flux of 1.0 MW/m² passes uniformly through the thick…Al₂O₃ grows even more slowly and is stable to high temperatures, so nickel-based superalloys, bond coats of thermal barrier coatings and Fe-Cr-Al heating elements are made to form Al₂O₃.
Which statement about the protective scales on heat-resista…Nickel-based superalloy Coefficient of linear thermal expansion Creep Thermal stress Deformation mechanism map Diffusion creep Larson–Miller parameter Parabolic rate law Pilling–Bedworth ratio Power-law creep