Thermal barrier coatings (TBC, TBP) - a type of coating used to insulate components, in particular, parts of gas turbine engines operating at elevated temperatures. Typical applications for coatings are turbine blades, combustion chambers, piping systems and nozzle guiding apparatus. TBP made it possible to increase the operating temperature of gas turbines, and therefore increase their efficiency.
TBPs are characterized by very low thermal conductivity, this is a coating that maintains a large temperature gradient when exposed to heat flux. The most commonly used material for TBP is yttrium stabilized zirconia (YSZ), which shows resistance to thermal shock and thermal fatigue up to 1150 ° C. YSZ is mainly applied by plasma spraying and electron beam physical vapor deposition ( ). HVOF high-speed flame spraying can also be used, in particular the wear-resistant properties of this material are also used to prevent blade wear .
Standard technology is aluminum and pre-coating the base material (usually heat-resistant alloys based on nickel or cobalt) with MCrAlY binder coating. The intermediate layer is necessary to compensate for residual stresses that might otherwise develop in the coating system, due to the difference in the thermal expansion coefficients of the metal base and ceramic TBP.
By the nature of the work of the part, thermal barrier coatings can be classified: a) cyclic temperature loads (for example, turbine blades of an aircraft engine) b) single temperature coatings (shells of guns).
The main problem of using thermal barrier coatings is the difference in the coefficients of thermal expansion of the materials of the part and the coating. With a large difference in the coefficient in the working temperature range of the part, cracking of the coating occurs, after which the part gradually loses its thermal barrier properties. This problem is solved by a more careful selection of materials.