Progress on high-temperature protective coatings for aero-engines

Aero-engine is a key part of aircraft, the operating temperature of which is being pushed to unprecedented levels for higher engine efficiency and performance. To accomplish higher gas-inlet temperature of aero-engines, applying thermal barrier coatings (TBCs) on hot-section metallic components, or even replacing some of the metallic components in aero-engines with ceramic-matrix composites (CMCs) and applying environmental-barrier coatings (EBCs) on them, are effective methods and have been widely accepted. On the other hand, increasing aero-engines operating temperature causes the aircraft more easily be detected, thus stealth coatings are necessary for engines. Except the hottest part in aero-engines, other parts may not need TBCs or EBCs due to the relatively low operating temperature, but they still need protection from oxidation and corrosion. Hence, corrosion-resistant coatings are essential. In this paper, the latest progress of the above high-temperature protective coatings, i.e., TBCs, EBCs, stealth coatings and corrosion-resistant coatings is reviewed, mainly including their materials, fabrication technologies and performance. In addition, due to the harsh operating environment, these protective coatings face many threats such as calcia-magnesia-aluminosilicates (CMAS) attack, causing premature failure of the coatings, which is also concerned in this paper. The work would provide a comprehensive understanding on the high-temperature protective coatings in aero-engines and guidance for developing advanced protective coatings for next-generation aero-engines.