Space engine blade TBC system

As a new generation of power units following steam engines and internal combustion engines, gas turbines integrate a series of high-tech technologies such as pneumatic system design, precision machining technology, and advanced material development. It is known as the "jewel in the crown" of the equipment manufacturing industry and is a measure of a country. An important indicator of the development level of heavy industry, it is also a powerful manifestation of a country's comprehensive national strength. Therefore, developed countries have always listed gas turbine manufacturing technology as a strategic industry to ensure national defense and energy security. At present, only three monopolies such as GE, Siemens and Mitsubishi Heavy Industries have gas turbine manufacturing capabilities. my country’s gas turbine manufacturing technology is still in its infancy, basically relying on “bundled bidding” to exchange technology from the market, and independent research and development capabilities in core technologies are still seriously insufficient. With the advancement of the "two major special projects" and the national 2025 plan, Chinese researchers are launching an assault on this "jewel in the crown", and the design and manufacturing of high-performance materials also play an important role in it.

With the development of gas turbines in the direction of high flow ratio, high thrust-to-weight ratio and high efficiency, the working temperature of gas turbines is also increasing. Take the M501J gas turbine developed by Mitsubishi Heavy Industries as an example. The inlet temperature of the turbine has reached 1600°C, while the operating temperature of the engine in the high thrust-to-weight ratio fighter can even reach above 2000°C. However, the limit operating temperature of nickel-based alloys used in high-temperature parts of gas turbines usually does not exceed 1000°C. Therefore, thermal protection of high-temperature components, especially turbine moving blades, is a key technology to ensure the service life and thermal efficiency of gas turbines.

At present, the most important means for thermal protection of high-temperature components of gas turbines is the combination of film cooling technology and thermal barrier coating technology. The former mainly introduces cooling air into the main flow through the complex airflow channels inside the alloy blades, which can reduce the surface temperature of the blades by 100~200°C. However, such a cooling effect still cannot meet the requirements of the gas turbine operating temperature, and at the same time, the cooling gas film will also take away part of the heat of the high-temperature gas, limiting the thermal efficiency of the gas turbine.

Thermal Barrier Coatings (TBCs) is to prepare a layer of "thermal barrier" on the surface of alloy blades to protect the alloy blades. At present, advanced thermal barrier coatings can reduce the surface temperature of the alloy by 200 to 300 °C. As shown in Figure 1, the thermal barrier coating usually has a double-layer structure, including a ceramic layer (topcoat) that bears most of the temperature gradient, about 100-400μm, and an alloy that provides bonding strength between the ceramic layer and the substrate. The bondcoat is about 100μm. In a high temperature environment, oxygen combines with the metal elements in the transition layer through the ceramic layer, and also forms a thermally grown oxide layer dominated by α-Al2O3 at the interface between the ceramic layer and the alloy bonding layer. In addition to bearing the internal temperature gradient of up to 1°C/μm, this thermal barrier coating also needs to bear the stress and strain generated during high-temperature thermal cycling, and resist the high-speed impact of inclusions and the thermochemical corrosion of high-temperature gas. . In order to maintain excellent thermal protection effect and service life, thermal barrier coating materials need to have the following key properties: low thermal conductivity, high stability, high thermal expansion coefficient, excellent comprehensive mechanical properties, and so on.