Real-time Detection And Mechanism Analysis Of Thermal Barrier Coating Failure Process Of High-speed Rotating Blades Under High Temperature Gas Thermal Shock

Thermal barrier coatings(TBCs)is an important thermal protection technology on the surface of turbine blades,and the development of TBCs has always been an important factor restricting the performance improvement of aero-engines.At present,TBCs technology has been widely used on the surface of gas turbine blades,but the TBCs still faces the huge problem of peeling off from the substrate surface.The life assessment test of the TBCs of the guide vanes is usually realized in the static environment simulator,but there has been a lack of suitable test equipment for the TBCs of the rotor blades.Carrying out the TBCs test on the ground table or core machine requires huge manpower and material resources,and cannot capture the key information of the coating damage evolution.Based on this,this paper develops an environmental simulator under the action of high-speed rotation and gas thermal shock.The flame spraying method is used to lay high-temperature resistance strain gauges and thermocouples on the surface of the rotor blade TBCs.The temperature field was used to analyze the damage evolution and failure mechanism of TBCs.The main innovative results achieved are as follows:(1)Based on the high-speed rotating turbine blade TBCs service environment simulation device and the TBCs damage real-time detection system designed by the team,reasonable thermal shock parameters and simulation device parameters are set.Through the cooperation of the gas spray gun and the high-speed motor,the thermal shock cycle of rapid cooling and rapid heating of the TBCs of the turbine blade is realized.The heating parameters of the superalloy substrate and the TBCs under different service states are calibrated,that is,the experimental parameters of heating to a predetermined temperature under different service speeds.The optimal strain measuring points and temperature measuring points are explored,and the temperature compensation of the high temperature thermal shock strain gauge is realized by developing a multi-functional liftable resistance furnace.(2)Based on the thermocouple and infrared thermal imager temperature measurement methods,the key temperature distributions on the surface of the TBCs during dynamic and static service were measured respectively.The research shows that the temperature of the leading edge of the TBCs is higher than that of the trailing edge,and the temperature of the suction surface is higher than that of the pressure surface during dynamic assessment.With the increase of service speed,the temperature of the TBCs surface decreased slightly.In the dynamic assessment,the temperature difference of the thermal barrier coating section is 103℃,which is higher than the section temperature difference of 243 ℃ in the static test.(3)Based on the measurement method of high-temperature resistance strain gage,the installation scheme of the resistance strain gage suitable for centrifugal load and thermal load was determined,and the strain evolution of the suction surface and the pressure surface during the high-speed rotation of the TBCs was measured respectively.The research shows that when the position of the strain measuring point is the same,the area close to the leaf crown has larger strain damage;With the increase of service speed,the maximum principal strain of the TBCs surface increases significantly,the overall leading edge deformation is larger than the trailing edge,and the suction surface is larger than the pressure surface.In the different measurement directions of the turbine blade,the direction parallel to the edge plate has the largest strain gradient.During a test run with sharp speed changes,the greatest deformation always occurs in the speed peak area.During the subsequent thermal fatigue cycle,the TBCs experienced 128 thermal cycle spalling failure with a principal strain evolution ranging from 0.23% to 0.82% before failure.Each measuring point is subjected to tensile deformation,which is higher than the strain evolution(0.04%-0.67%)of the static thermal shock assessment under the same state.The failure position is near the leading edge of the blade back.The failure causes are the impact of external force and the rapid expansion of various cracks under the action of centrifugal load.Coating failure occurs in the form of thinning spalling,which eventually detaches from the bondline.