The Failure Mechanism Of High-speed Rotating EB-PVD Thermal Barrier Coating Under High Temperature Gas Thermal Shock

Thermal barrier coatings(TBCs)are recognized as essential materials for high performance aero-engine and gas turbine turbine blades due to their excellent thermal protection performance.The development of thermal barrier coating technology determines the performance of the engine.In essence,the progress of technology depends on how to effectively solve the problems of premature spalling of thermal barrier coating and large dispersion of life,which is particularly prominent in the highspeed rotating blade.After years of research and development at home and abroad,the static failure mode of thermal barrier coatings with simple shape and single load has been basically mastered,but there are few reports on the experimental study of failure mode of high-speed rotating thermal barrier coatings.Therefore,an environmental simulation and testing device for thermal barrier coatings on high-speed rotating turbine blades was first built in this paper.Based on this experimental device,the influences of rotational speed,temperature and curvature radius on the macroscopic service life of electron beam physical vapor deposition(EB-PVD)were studied.The microscopic failure behaviors of thermal barrier coatings were further analyzed by means of scanning electron microscope(SEM)and energy dispersive X-ray(EDS).Finally,based on the fluid-solid coupling numerical simulation method,the failure mechanism of the high-temperature and high-speed rotating EB-PVD thermal barrier coatings were summarized.The specific research content and innovative results are as follows:(1)Based on the thermal barrier coating environment simulation and testing device for high-speed rotating turbine blades,the service environment simulation of thermal barrier coatings under the interaction of high-speed rotation and high-temperature gas is realized.By using the color temperature measurement method of evenly coating temperature indicating paint on the surface,real-time contact temperature measurement method of embedded thermocouple,the surface temperature distribution of thermal barrier coating under high-speed rotation working conditions was obtained as750～800℃,850～900℃ and 950～1000℃.(2)The macroscopic test results show that the changes of rotational speed,gas temperature and curvature radius have significant effects on the service life of thermal barrier coatings.As the speed increases from 0 r/min to 5000 r/min,the service life decreases from 251 cycles to 12 cycles.With the gas temperature increases from750～800℃ to 950～1000℃,the service life decreases from 65 cycles to 12 cycles.As the increase of curvature radius from 5 mm to 9 mm,the service life increases from 12 cycles to 76 cycles.The microscopic results show that the failure mode of the highspeed rotating thermal barrier coating is mainly the fracture failure of the ceramic layer itself,supplemented by the interface failure.Specifically,the columnar crystal region of ceramic layer usually show a “stepped” mode of thinning and peeling,or the failure mode of laminar peeling in the equiaxed crystal region caused by the encounter of vertical/tangential cracks in the columnar crystal region and transverse cracks in the equiaxed crystal region.(3)Based on the numerical simulation method of fluid-structure coupling,the service environment of thermal barrier coatings under high-speed rotating operation is highly restored.The flow field cloud diagram showed that the high speed rotation directly changed the overall direction of the high temperature air flow,resulting in the air flow angle deflection on the thermal barrier coating surface.The temperature field cloud showed that the high speed rotation increased the coupled heat transfer frequency and improved the overall cooling effect of the coating surface.The stress cloud diagram and experimental analysis results showed that the spalling failure of high-speed rotating thermal barrier coatings was driven by centrifugal force and shear stress.The failure mechanism diagram of high-speed rotating EB-PVD thermal barrier coatings was summarized on this basis.