Review on thermal spraying powder with hierarchy pore structure and a new generation of long-life thermal barrier coating materials

Thermal barrier coatings, which are widely used in aero-engines and gas turbines, can reduce the surface temperature and improve the effective service time of superalloy due to low thermal conductivity and good temperature resistance. The performance and lifetime of the thermal barrier coating are directly affected by the material and structure of the ceramic top coating. The method of adjusting the microstructure of ceramic coating with controlled raw material powder can reduce the strain-stress mismatch in the coating, and has the advantages of flexible operation, remarkable effect and wide control range. In order to solve problems of low strain tolerance and insufficient thermal shock resistance in traditional coatings, our team successfully has prepared ceramic microspheres with hierarchy pore structure by using electrostatic spraying combined with phase inversion theory（ESP）. Compared with traditional hollow microspheres, the ESP microstructure of nano-pores and finger-like pores lead to high sintering resistance, low thermal conductivity, high specific strength and >95% thermal reflectivity. With the retention of the hierarchy structure, the coating has good fracture toughness and strain tolerance, where the thermal cycle life of the coating is increased by more than ~2 times. ESP technology provides a fast feedback control method for new thermal barrier coating materials from material design to engineering application, such as rare earth zirconate, rare earth tantalate and rare earth doped YSZ high entropy system. With the in-depth study of material mechanics, optics, thermodynamics and the precise control of internal topological structure, the hierarchy pore structure will be more widely used in aerospace, military defense, fluorescence temperature measurement and other fields in the future.