| In aero engine design and verification process, surface temperature and temperature distribution on the hot components(such as turbine blades) are very important to their mechanical strength and working life. How to achieve on a real-time and accurate measurement in the harsh environment of working engine has become the urgent technical problem to be solved. Compared with the limitation of the traditional method, thin film thermocouples overcome the disadvantages of interference to the flow field and damage to the mechanical structure. The thin-film thermocouples are directly prepared on the surface of components to be tested, and integrated by thin film deposition techniques. Therefore, they have characteristics of small structure size, no influence on the test environment, fast response, small thermal capacity and so on, which obviously have advantages in the measurement of surface temperature. The S-type thin film thermocouples composed of PtRh and Pt materials, that have a wide temperature measurement range and a stable thermoelectric performance, are one of the most promising temperature measuring devices. On the basis of previous work, the preparation and properties of PtRh and Pt thin films and S-type thin film thermocouples were studied in this paper:Firstly, PtRh and Pt thin films were deposited by magnetron sputtering method on alumina ceramic substrate, and were systematicly studied of the effect of substrate temperature, film thickness and annealing treatment on PtRh and Pt thin films’ surface morphology, electrical properties and crystal structures. The results showed that with the increase of substrate temperature, the structure of PtRh and Pt thin films tended to be denser, and their resistivity was decreased to 3.34×10-5 Ω·cm and to 1.89×10-5 Ω·cm, respectively when the substrate temperature was up to 400 ℃. With the increase of film thickness, the electrical properties of the two kinds of thin films were practically stable. The densification of PtRh and Pt thin films was further improved after annealing treatment, and the resistivity was kept stable while the anneal temperature was higher than 800 ℃ and anneal time was more than 60 min. PtRh thin film deposited at the substrate temperature of 400 ℃, had a certain degree of rhodium oxidation phenomenon on its surface, under the condition of atmospheric environment of 900 ℃, which conversed back to rhodium element at higher temperature than 1000℃.Secondly, S-type thin film thermocouples were prepared on alumina ceramic substrates, and were studied of the influence of substrate temperature, film thickness and annealing treatment on S-type thermocouple thermoelectric properties through a series of static calibrations. The results showed that the scattering coefficient of the S thin film thermocouples’ Seebeck coefficient was obviously decreased at 400 ℃ substrate temperature, and the corresponding output of thermoelectric power is improved by 6.78% at 1000 ℃. Increased thin film thickness effectively improved the stability of S-type thin film thermocouples and the Seebeck coefficient remained basically unchanged; Vacuum annealing treatment at 800 ℃ further reduced the scattering coefficient, and output thermal potential at 1000℃ increased by 9.08% compared to unannealed condition. While substrate temperature was 400 ℃, thin film thickness was 1 μm and vacuum annealing treatment was at 800 ℃ for 60 min, the average Seebeck coefficient of S-type thin film thermocouples in range of 300℃ to 1000℃ reached to 12.10 μV/℃, sensitivity of K value was higher than 0.9 in general and the relative error at maximum temperature gradient was-1.85%.Finally, S-type thin film thermocouples were prepared on nickel-based superalloy and turbine blade. The device structure was composed of NiCrAlY alloy transition layer, thermally grown Al2O3 layer, Al2O3 insulation layer and functional layer, respectively. Results showed that in the temperature range of 300 ℃ ~1000 ℃, the thermal electromotive force of S-type thin film thermocouples on nickel-based alloy had great linearity and repeatability. The average Seebeck coefficient was 10.16 μV/℃ and the K value stabilized from 0.84 to 0.90 which were less than that on alumina due to the increased heat exchange rate with metal substrate, while the relative error at maximum temperature gradient was-0.52%. S-type thin film thermocouples prepared on the surface of turbine blade had been tested in static calibration and been applied in cooling effectiveness test, which maintained the structure of the thermocouples and had a good device performance. |
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