Case study of thermal barrier coating

 Thermal barrier coating (Thermal barrier coatings, TBCs) is a protective coating used in high temperature environment such as turbine blade, combustion chamber wall and tail nozzle of aero engine. Different from the traditional protective coating structure, the thermal barrier coating usually consists of a metal bonding layer and a layer of ceramic insulation layer, sometimes adding oxygen barrier layer, sealing layer and gradient layer to form a multi-layer structure or gradient structure. The structure diagram is shown in Figure 5. The bonding layer in the thermal barrier coating mainly plays the role of alleviating the mismatch of the thermal expansion coefficient between the ceramic layer and the matrix, and improving the physical compatibility between the two, while the main ceramic layer directly faces the external high temperature environment, which needs to have low thermal conductivity, high expansion coefficient and high thermal stability. At present, the most commonly used ceramic layer material is YSZ, but 1200℃ is the limit of the use of this material. When the temperature exceeds the limit temperature, ZrO 2 will be phase change, leading to a certain expansion of the coating, affecting the use of the coating. In recent years, new ceramic layer materials developed for thermal barrier coating mainly include YSZ, GdYSZ, La2Zr2O7, CePO 4, etc. The specific physical parameters of coating are shown in Table 2. As can be seen from the names of the materials in the table, the thermal barrier coating ceramic materials can be mainly divided into rare earth doped YSZ, rare earth doped zirconate, rare earth phosphate, rare earth silicate, etc. The use temperature of the rare earth doped YSZ material is significantly higher than that of the traditional YSZ material, because the doped rare earth oxide increases the lattice distortion of ZrO2, which reduces the thermal vibration frequency of the lattice, and reduces the thermal conductivity when the thermal expansion coefficient of the coating is basically unchanged.