| Accurate high-temperature measurement can provide assurance for the working performance and safe operation of high-temperature equipment.Currently,the demand for surface temperature measurement of high-temperature components is increasing,and excessive temperature can pose a certain threat to the safety of high-temperature equipment.Therefore,real-time monitoring of surface temperature of high-temperature components is of great significance for its safety monitoring and performance verification.Compared to armored thermocouple wires,thermocoupled surface temperature measurement sensors do not require special processing and fixation of their mounting locations,and do not damage the mechanical structure of the object being measured.They have the advantages of small thickness and volume,fast response speed,and high measurement sensitivity.At the same time,because of their excellent chemical and electrical stability in high-temperature oxidation environments,they have no impact on combustion aerodynamics in the engine,Ideal for surviving in harsh environments and monitoring the temperature of high-temperature component surfaces.Currently,high-temperature components can be roughly divided into two categories,one is new ceramic components,and the other is traditional metal components mainly made of nickel based alloys.This thesis takes the surface temperature measurement of hot end components of high-temperature equipment as the application background.Aiming at ceramic high-temperature components,pulsed laser deposition technology was used to prepare high-temperature conductive thin films and the preparation process of thin films was studied.For the first time,pulsed laser deposition technology was used to prepare ceramic based thin film thermocouples and its thermoelectric properties were deeply studied;Considering the miniaturization design and practical application environment of thermocouples for metal high-temperature components,S-type thermocouples were fabricated on nickel based alloys using a thick film integrated process.The main contents and conclusions are as follows:(1)The preparation process of pulsed laser deposition of ITO thin films was studied,mainly focusing on the effects of deposition temperature,target substrate distance,sputtering atmosphere,and other process conditions on their resistivity and deposition rate.The results show that the ITO thin film prepared by PLD has a novel nano conical structure.The higher the substrate temperature is deposited,the faster the deposition rate of the ITO thin film is.The resistivity of the thin film gradually decreases due to the increase in oxygen vacancy concentration,and reaches a minimum at 600 ℃;Target base distance can affect the uniformity of thin film deposition.When the target base distance is 6.5 cm,the deposition rate of ITO thin film is the fastest and the resistivity is the smallest;The higher the nitrogen pressure of sputtering,the slower the deposition rate of ITO films,and the lower the resistivity due to the reduction of defects in the films.(2)The ITO films were heat treated by different annealing processes.The effects of annealing time,annealing temperature and annealing atmosphere on the thermoelectric properties of the films were studied.The results show that the higher the atmospheric annealing temperature,the lower the oxygen vacancy concentration in ITO films,and the higher the resistivity;The longer the annealing time in the atmosphere,the higher the resistivity of ITO film due to the lower carrier concentration.At the same temperature,nitrogen annealing results in larger grain size,fewer defects and lower resistivity of ITO films.(3)Pt-ITO thin-film thermocouple samples were prepared on Al2O3 ceramic,and the samples were statically calibrated in the temperature range of 25~1300 ℃.The effects of annealing,substrate roughness and protective layer on the thermoelectric properties of the samples were mainly studied.The results show that the Pt-ITO thin film thermocouple has good thermoelectric repeatability at 25~1300 ℃,the maximum repetition error is ±1.45%,the maximum operating temperature can reach 1400 ℃,the average Seebeck coefficient is more than 50 μV/℃ at 1300 ℃,and has good thermal stability at 1150 ℃,and the drift rate is7.97 ℃/h for 30 minutes.In addition,the response time shall not exceed 435 μs。Annealing treatment can effectively improve the thermoelectric stability of the thin film thermocouple,and the Seebeck coefficient and thermoelectric potential output of the thermocouple increase.The thermoelectric stability of the thin film thermocouple sample prepared on the substrate with smaller roughness is better,but it has little influence on the thermoelectric potential output.The sample with Al2O3 protective layer has better temperature resistance and better thermoelectric performance than the sample without protective layer.(4)The S-type thermocouple samples were prepared on the nickel-base alloy substrate,and the static calibration was carried out in the temperature range of 25~1000 ℃.The results show that the composite insulation layer prepared by various processes has good insulation performance,which is greater than 1 GΩ before 105 ℃ and 50 kΩ at 1000 ℃;The designed temperature sensor has good linearity within 25~1000 ℃,and the average Seebeck coefficient is 9.016 μV/℃,slightly lower than the Seebeck coefficient of standard S-type thermocouple(9.352 μV/℃),the limit output is 13.11 m V at 1400 ℃,and it can work stably for more than10 h at 1100 ℃. |
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