Measurements and Applications of Thermal-Mechanical Properties of Thermal/Environmental Barrier Coating Materials

As the operating temperatures of aero-engine and gas turbine combustion chambers continue to rise, the high-temperature components face increasingly harsh service environments. The designed inlet temperatures of gas-turbine engines of advanced fighter jets have reached 1900 ℃, when the working temperatures of combustion chamber of H-level heavy-duty gas turbines have approached 1600 ℃, which are far higher than the limited application temperatures of Ni-based alloys (1150 ℃). Besides, the high-temperature components, such as rotating blades in the combustion chambers, are subjected to high-speed rotations, erosions of high-speed particles, thermal corrosions, thermal cycling stress, and corrosions of melted oxides, which will further lead to premature failures of these components. To overcome these challenges, ceramic thermal/environmental barrier coatings (T/EBCs) are widely used on surfaces of high-temperature components of gas turbines and aircraft engines to provide specific protections. The T/EBC systems are consist of substrates (high-temperature alloys or ceramic matrix composites), bond coat (BC) and surficial ceramic thermal/environmental barrier coatings. The main functions of T/EBCs are to provide thermal insulation performance, resisting particle impact, anti-oxidation, anti-corrosion, and so on. In order to maintain the excellent thermal insulation performance and exhibit a long-term service life, ceramic T/EBCs must display a low thermal conductivity, thermal expansion coefficients matching to those of different substrates, extraordinary high-temperature stability, high toughness and hardness, as well as relatively low modulus. It is of great significance to effectively measure and calculate the key mechanical and thermal properties of various potential T/EBC materials, which can promote the investigation and application of high-performance T/EBCs. In this work, we analyze and discuss the measurements and calculation methods of various mechanical and thermal properties of ceramic T/EBCs in detail, including hardness, elastic modulus, fracture toughness, thermal expansion coefficients, and thermal conductivity. For mechanical properties, the Vickers hardness device, nano indentation, and the ultrasonic reflection method are used to measure hardness, elastic modulus, and fracture toughness. For thermal properties, the thermal expansion device and high-temperature X-ray diffraction are used to calculate the thermal expansion coefficients, and their differences are discussed. Specifically, four different models are discussed in detail to elucidate the theories and calculations of thermal diffusivity, and the choosing rules of different models are proposed based on their calculation principle, which are good for obtaining reliable thermal conductivity. The object of this work is to provide scholars with suitable measurements and calculation methods of various mechanical and thermal properties for T/EBC materials, which can advance the quick screening, investigations, and designs of high-performance TBCs.