Development Of Thin-film Heat Flux Sensor From Polymer-derived SiCN

The heat flux test on the surface of the turbine blades of aero engines can provide the basis for blade design,and can also be used as one of the basis for monitoring and predicting blade failure.It is extremely difficult to install discrete devices on the surface of turbine blades of aero engines,for it will damage the surrounding flow fields and affect pneumatic design.The thin-film heat flux sensor has the advantages of no disturbance,fast response and small size,and can be used for heat flux testing on the blade surface.The thin-film heat flux sensor prepared by the traditional PVD process is less adaptable on the curved surface and can withstand lower temperature.Polymerderived Ceramics(PDC)have high temperature resistance and extreme heat shock resistance,which are easy to mold and have the potential to prepare thin-film heat flux sensors.In this paper,the research and development of PDC-SiCN thin-film heat flux sensor designed for application in turbine blades of aero engines are carried out,and the main research work and results are as follows:(1)According to the theory of measuring heat flux with thin-film heat flux sensor,the structure size of PDC-SiCN thin-film heat flux sensor is designed.Based on the analysis of the thermal,mechanical and electrical properties of PDC-SiCN material,the film layer system on Al2O3 and nickel-based alloy substrate,including insulation layer,thermistor layer,thermal resistance layer and protective layer,was determined.The research of single process and fusion process of each film layer is carried out,and the process scheme and law of multilayer film based on temperature resistance effect are mastered,which lays the technological foundation for the preparation of heat flux sensor.(2)Based on the conductivity mechanism of PDC-SiCN,the effects of process parameters and material parameters on the conductivity mechanism were studied.The effects of pyrolysis temperature,components and atmosphere on the thermal resistance characteristics of thin films and their conductivity mechanism were mastered,which provided support for improving the sensitivity of heat flux sensors.(3)After summarizing and analyzing the anti-oxidation mechanism of PDC-SiCN,the oxidation behavior of nitrogen pyrolysis and vacuum pyrolysis films in the air at 800℃ and 900℃ was studied,revealing the anti-oxidation mechanism of sensitive films pyrolyszed in low-degree vacuum,and understanding the anti-oxidation law of protective layer and vacuum pyrolysis sensitive films.PDC-SiCN thin-film thermistor with temperature resistance of 800℃ was successfully prepared for the first time,which laid a technical foundation for temperature resistance improvement of heat flux sensors.(4)Combined with the designed structure size and the obtained conductive mechanism and oxidation resistance mechanism,the PDC-SiCN thin-film heat flux sensors on alumina substrate and PDC-SiCN thin-film heat flux sensors on nickel alloy substrate were prepared.The steady-state and dynamic properties were studied.The results show that the sensitivity of the developed heat flux sensors with alumina and nickel alloy substrate increase with the increase of thermal resistance layer thickness,and the response frequency decreases with the increase of thermal resistance layer thickness,which verifies the feasibility of design,manufacture and application of PDC thin-film heat flux sensors.