Development Of ITO-In₂O₃ Thin Film Thermopile Heat Flux Sensors

The turbine blades of aeroengine work in the harsh environment of high temperature,high speed and large heat flux,and bear severe thermal shock,which is easy to cause thermal fatigue failure of blades,such as ablation,cracking,leakage of air flow in the tip clearance,which causes engine failure.Measuring the surface heat flux on turbine blades can be used to evaluate the heat transfer capacity of turbine blade,provide important data for optimizing the structural design of turbine blades,realize online real-time monitoring of the working state of aeroengine,and improve the safety of aerocraft.In order to solve the problem that the traditional block type heat flux sensors can’t meet the heat flux measurement demand of turbine blades,ITO/In2O3 thin film thermopile heat flux sensors are prepared by magnetron sputtering technology in this paper.According to the working principle of the thin film heat flux sensors,three kinds of thin film heat flux sensors with different structures,i.e.plane ring structure,vertical structure and step structure,are designed.The heat transfer process of the three kinds of structure sensors is analyzed,and the conclusion that the time constants of the three kinds of structure heat flux sensors decrease in turn is drawn.ITO/In2O3 thin film thermocouple was developed first,and its temperature measuring range was 1050℃,and its sensitivity was 200 μV/℃.Three kinds of structure thin film heat flux sensors were prepared by magnetron sputtering on alumina substrate.According to the testing requirements of different heat flux range,two kinds of testing platforms with different heat flux range were built.The range of the three kinds of structure thin film heat flux sensors was over 213.8 kW/m2,and the applicable temperature was over 794℃.The steady-state response time constants of the thin film heat flux sensors with planar ring structure,vertical structure and step structure decrease gradually,which are 7.8 s,2.9 s and 0.9 s,respectively.It’s consistent with the theoretical analysis.The cut-off frequency of the thin film heat flux sensor with the planar ring structure on the alumina substrate is 3700 Hz.Thin film heat flux sensors was fabricated on nickel-based alloy substrate.SEM and XRD were used to obtain the microstructure,composition and phase changes of the transition layer films before and after high temperature treatment.Al and O elements increased significantly after high temperature treatment.Combined with the XRD pattern,Al elements precipitated on the surface of NiCrAlY transition layer after high temperature treatment were oxidized to Al2O3.Ni3Al(112)was the main phase of NiCrAlY film,and the diffraction peak increased significantly after high temperature treatment.The longitudinal insulation resistance of the insulating layer at room temperature had been measured over 120 MΩ,and it reduces as the temperature rises.When the temperature rises to 720℃,the longitudinal insulation resistance is about 11 kΩ.The experimental results showed that the limit applicable temperature of thin film heat flux sensors on nickel-based alloy substrate reached 936℃ and the heat flux range exceeded 266.05 kW/m2.