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thermal barrier coating
Thermal barrier coatings (TBC) are highly advanced materials systems usually applied to metallic surfaces, such as on gas turbine or aero-engine parts, operating at elevated temperatures, as a form of ''exhaust heat management''. These coatings serve to insulate components from large and prolonged heat loads by utilizing thermally insulating materials which can sustain an appreciable temperature difference between the load-bearing alloys and the coating surface. In doing so, these coatings can allow for higher operating temperatures while limiting the thermal exposure of structural components, extending part life by reducing oxidation and thermal fatigue. In conjunction with active film cooling, TBCs permit working fluid temperatures higher than the melting point of the metal airfoil in some turbine applications.
==Structure==
Thermal barrier coatings typically consist of four layers: the metal substrate, metallic bond coat, thermally grown oxide, and ceramic topcoat. The ceramic topcoat is typically composed of yttria-stabilized zirconia (YSZ) which is desirable for having very low conductivity while remaining stable at nominal operating temperatures typically seen in applications. Recent advancements in finding an alternative for YSZ ceramic topcoat identified many novel ceramics (rare earth zirconates) having superior performance at temperatures above 1200 °C, however with inferior fracture toughness compared to that of YSZ. This ceramic layer creates the largest thermal gradient of the TBC and keeps the lower layers at a lower temperature than the surface.
TBCs fail through various degradation modes that include mechanical rumpling of bond coat during thermal cyclic exposure, especially, coatings in aircraft engines; accelerated oxidation, hot corrosion, molten deposit degradation. There are issues with oxidation (areas of the TBC getting stripped off) of the TBC also, which reduces the life of the metal drastically, which leads to thermal fatigue.
The TBC can also be locally modified at the interface between the bondcoat and the thermally grown oxide so that it acts as a thermographic phosphor, which allows for remote temperature measurement.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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