| Due to its low mass/size ratio, rapid response, minimal gas flow distortions and negligible structural damage, thin film thermocouples(TFTCs) were widely used in aero-engine and turbines as advanced temperature measurement technique. In this dissertation, different types of TFTCs were fabricated according to the requirements of surface temperature measurement of aero-engine. The fabrication process of the buffer layer, insulating layer and TFTC layer was studied and the thermoelectric performance of TFTCs was investigated in detail. Three kinds of TFTCs which adapt to mid temperature(200 ~ 600 °C), high temperature(500 ~ 1000 °C) and ultra-high temperature(more than 1000 °C) region, respectively, were prepared and stable performance was achieved for all of them.In order to meet the requirement of aero-engine test, a prerequisite is to achieve the good adhesion of insulating layer of TFTCs with the bottom layer. Ni Cr Al Y buffer layer with 10 μm in thickness was deposited on nickel base superalloy. The influences of segregation and oxidation processes on the micro structures of Ni Cr Al Y films were investigated systematically. It turns out that aluminum segregates as Al-rich particles on the surface of Ni Cr Al Y film, resulting in island-like and loose alumina layer after oxidation, which leads to poor adhesion of the insulating layer. In order to achieve continuous and dense alumina layer, the aluminum film with thickness of 50 nm was sputtered on top of Ni Cr Al Y film after the segregation process. Using Ni Cr Al Y film and thermally grown alumina layer as the buffer layer, the transition from nickel-based superalloy to insulating layer was realized and the adhesion of insulating layer was improved. After that, 10 μm thick alumina film was deposited on the thermally grown alumina by e-beam evaporation with oblique angle deposition(OAD). This insulating layer sustains up to 1100 °C for more than 5 hrs. The insulation performance is over 100 MΩ at room temperature while 5.2 kΩ at 1100 °C.The fabrication of Ni Cr/Ni Si(K type) TFTCs on nickel-based superalloy was studied. The influences of process parameters on the thermoelectric performance of K type TFTCs were investigated in detail. Seebeck coefficient of K type TFTCs increased 29% by vacuum annealing at 600 °C for 60 min and decreased 25% by reducing the film thickness from 1 μm to 500 nm. K type TFTCs was fabricated on nickel-based superalloy with optimized processes, and it showed good repeatability, uniformity and linearity. Seebeck coefficient of TFTCs is 38.4 μV/°C. The coefficient of sensitivity(K) is above 0.8. The life time of TFTC is more than 10 hrs. After numerical correction, the error of temperature measurement at mid temperature region is less than ±2.5%. The Seebeck Coefficient of K type TFTCs fabricated on turbine blade is 38 μV/°C under static test. The cooling effect test of TFTCs was performed with pressure, temperature, flow mass, input and output Mach number and test time as 0.6 MPa, 600 °C, 0.85 kg/s, 0.26, 0.85 and 150 min, respectively. After the test, the structure of K type TFTCs is intact and still showed good adhesion. However, due to the oxidation at high temperature, the thermoelectric performance of K type TFTCs degenerated. Therefore, the development of high temperature TFTCs is required.Pt/Rh-Pt(S type) TFTCs were investigated in order to meet the requirement of temperature measurement at high temperature region. The influences of process parameters on the thermoelectric performance and life time of S type TFTCs were investigated in detail. The results showed that, annealing under vacuum improved the thermoelectric performance of TFTCs obviously. The reduction of the thickness of Pt/Rh-Pt film resulted in significant life time increment of S type TFTCs. S type TFTCs fabricated on nickel-based superalloy with optimized processes showed good linearity. The Seebeck Coefficient is 8.1 μV/°C. The K value is about 0.77. The life time is more than 10 hrs. After correction, the error of temperature measurement is less than ±4%. The Seebeck Coefficient of S type TFTCs fabricated on turbine blade is 8 μV/°C under static test. While during the cooling effect test, the adhesion of S type TFTCs is not as good as K type TFTCs. It can be ascribed to the oxidation of Rh element under ultra-high temperature, which limited the application of the K type TFTCs.In order to improve the endurance of the TFTCs under ultra-high temperature region, the Pt Rh film was replaced by ITO thin film in S type TFTCs. And the fabrication of ITO thin films was investigated systematically. When annealed at 1000 °C, Sn element segregated to the surface of ITO film and volatilized, leading to increased resistivity of the film and the degeneration of thermoelectric performance. To avoid the oxidation of ITO thin film at high temperature, Si3N4 films were prepared and served as oxidation resistance layer. And the diffusion of the oxygen atom was effectively obstructed by Si3N4 films. At the same time, the increase of resistivity in ITO thin films was observed, which can be correlated to the nitrogen diffusion from Si3N4 to ITO film. The influences of N doped on ITO thin film were analyzed. Within certain partial pressure region of nitrogen, the stability of ITO thin films increased with increasing partial pressure of nitrogen. The optimized partial pressure of nitrogen is 40%. The ITO/Pt TFTCs were fabricated on nickel-based superalloy with optimized processes. And the static calibration showed that the Seebeck Coefficient is 78.32 μV/°C. The life time of TFTCs is more than 20 hrs. The error of temperature measurement is less than ±1.5% even when the temperature is over 900 °C. ITO/Pt TFTCs were also fabricated on nickel-based turbine blade, and the adhesion of TFTCs was evaluated during the cooling effect test. ITO thin films showed good adhesion with the turbine blade and no delamination was observed.In summary, in order to meet the urgent needs of surface temperature measurement during R&D of turbine engine, TFTCs with excellent performance were fabricated and integrated on turbine blades. And this provides the technical foundation for precise surface temperature measurement of turbine blades. |
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