Real-time Synchronous Detection And Mechanism Analysis Of High Thermal Shock Failure Of Thermal Barrier Coating

Thermal barrier coating is an indispensable thermal protection technology for high-performance aeroengines and a key thermal insulation technology in the world aviation propulsion program.It has been widely used in aeroengine turbine vanes.However,the thermal barrier coating faces a huge bottleneck of spalling failure.Due to the lack of a suitable thermal barrier coating service environment simulation device and real-time detection method,the failure mechanism of the turbine vane thermal barrier coating is still unclear.Based on this,this paper uses a variety of detection methods to detect the thermal shock process of the turbine vane thermal barrier coating in real time,and the main innovative results obtained are as follows:(1)Based on the thermal barrier coating service environment simulation device independently developed by the research group,reasonable thermal shock parameters and device parameters were set to realize the thermal shock cycle of rapid thermal barrier cooling of the turbine vane thermal barrier coating.The infrared emissivity of the high-temperature alloy substrate and the thermal barrier coating at different temperatures were calibrated,and the temperature distribution and temperature change of the thermal barrier coating of the turbine vane during the insulation period were measured.Studies have shown that the emissivity of superalloys decreases with increasing temperature,and the emissivity of thermal barrier coatings increases with increasing temperature.The leading edge of the vane has the highest temperature distribution,followed by the pressure surface and the lowest suction surface.The maximum temperature rise rate of the thermal barrier coating of the turbine vane can reach 100℃/s.(2)Based on the acoustic emission detection technology,the damage evolution of the thermal barrier coating until the spalling failure occurs.And record the macro and micro morphological changes of the thermal barrier coating.Studies have shown that five failure modes can be distinguished based on the spectrum of the acoustic emission signal,namely vertical cracks on the surface(200-220 k Hz),shear-type interface cracks(300-325 k Hz),and open interface cracks(400-450 k Hz),Base deformation(90-110 k Hz)and noise(20-60 k Hz).The cracks were analyzed qualitatively and quantitatively,and the open interface cracks and shear cracks were dominant.The thermal shock life of the thermal barrier coating is 710 cycles.The peeling area is located in the middle of the leading edge.There are a lot of dark spots caused by insufficient combustion of kerosene.The amount of TGO and the thickness of TGO are significantly larger than the unstripped area.(3)Based on the Digital Image Correlation(DIC)method,the optimal parameter design for the preparation of high-temperature thermal shock speckles was obtained,and the main strain changes of the suction surface and the pressure surface were measured respectively.Studies have shown that with the increase of the number of thermal shock cycles,the main strain gradually increases,from compressive strain to tensile strain.The strain of the thermal barrier coating in the middle in the vertical direction is higher than the strain on both sides.To further clarify the failure mechanism of the thermal barrier coating,as the number of thermal shock cycles increases,the main strain on the surface of the thermal barrier coating changes from compressive strain to tensile strain,a huge temperature gradient and the existence of stress concentration around the membrane hole,The diffusion and coalescence of surface and interface cracks during the cooling stage.