| Aircraft engine is known as the heart of a plane. Meanwhile, it is a key point of China’s aviation industry research. In recent years, with the development of advanced materials technology of high temperature alloy and advanced manufacturing technology of blade machining, testing the aircraft engine blade’s state parameters is required in urgent. In all testing techniques, the thin film sensor is deposited on the surface of the blade, which has some advantages, such as light quality, small damage for the blade’s structure strength, small disturbance for the flow channel and so on. So it is the advanced testing technology of the aircraft engine. In order to ensure the sensor can work in a harsh environment, where the blade should undergo high pressure, severe airflow washout and high temperature of 1000 ℃. In addition, it not only requires the film sensor must have good adhesion, but also ensure good electric insulation characteristics between the sensor and the metal blade under high temperature. Therefore, the study of the insulation film which has electrical isolation effect on the metal blade and the sensor is important. The dissertation is based on the need of China’s aircraft engine blade’s state parameters testing, according to the research task of the thin film sensor, around the preparation technology of insulation film, research work has been carried out, which provides a key technical support for the thin film sensor’s research.The alumina(Al2O3) thin film has a good chemical stability and mechanical stability, good wear resistance, high hardness, high melting point, high dielectric constant, and stronger anti-irradiation, which is widely used in microelectronics, optical coatings, a dielectric layer, a protective layer, high speed cutting tool etc.. The Al2O3 is one of dielectric materials of the large bandgap(approximately 9eV), besides the Al2O3 has a good resistance in the high temperature. The above properties make Al2O3 is one of good choice of insulating material between metal blade and sensor. Al2O3 thin films are deposited by electron beam evaporation deposition in this dissertation. The microstructure evolution, porosity, thermal conductivity, electrical conductivity and residual stress of Al2O3 thin films aresystematically discussed. The film shows good temperature insulation characteristic by exploring the insulation characteristics of compound film that consists of different materials. The dissertation contains the following sections:The Al2O3 thin films are prepared by electron beam evaporation. Oblique angle deposition(OAD) technique regulates Al2O3 microstructure. It is systematically studied the effect of the inclined angle, deposition temperature, deposition rate, and film thickness on the surface roughness, and the crystal orientation. The porosity of different microstructures of Al2O3 thin film is also studied. The refractive index at the range of the wavelengths from 400 nm to 800 nm is calculated using the envelope method and the Cauchy dispersion relation. The effective porosity is calculated using the Bruggeman effective medium approximation theory(BEMA), which varies with different inclined angles and deposition temperatures.Based on the microstructure of Al2O3 thin films is controlled effectively, the residual stress of Al2O3 thin films with the different microstructures is studied by the Stoney equation. The deposition temperature, deposition rate, and film thickness have effect on the residual stress of Al2O3 thin films. The thermal conductivity of Al2O3 thin films of different thickness and inclined angle is measured by 3ω method. So we can select appropriate inclined angled and deposition conditions to obtain low residual stress and thermal conductivity.The insulating properties of Al2O3 thin film with the different microstructures are studied. The characteristics of I-V curves for alumina thin film at different inclined angles are measured, which has relation with the inclined angle. The conductivity of Al2O3 thin film is calculated by Ohm’s law. The conductivity and resistivity are correlated with the inclined angle, which plays a guiding role on high temperature insulation properties of Al2O3 thin films.The MgO thin films are prepared by Oblique angle deposition(OAD) technique. It is studied that the inclined angle has an influence on the texture of MgO thin films. The residual stress of MgO thin films of the different microstructures is studied by the Stoney equation. The Al2O3 and MgO composed thin films are prepared. The characteristics of I-V curves for composite film are tested. The insulation layer construction method is explored.In view of the fact that the MgO thin films deposited by oblique angle deposition technique have the preferential orientation, this paper introduces an MgO thin film as a buffer layer and a filling layer, therefore, the MgO thin films are prepared using electron beam with oblique angle deposition technique. The microstructure and texture of the MgO thin films are studied. It is studied that the inclined angle has influence on the texture of MgO thin films. The residual stress of MgO thin films with the different microstructures is studied by the Stoney equation. The Al2O3 and MgO composite thin films are prepared by oblique angle deposition technique. The characteristics of I-V curves for composite film are tested. The insulation layer construction method is explored. The discovery of MgO as a filling layer combined with Al2O3 is better. This combination is used in this dissertation. The MgO is easy to deliquescence, so the composite film of different microstructures of Al2O3 is prepared by oblique angle deposition technique. The electrical conductivity of composite thin films of the different microstructures of Al2O3 thin films is tested in the temperature range from 300 K to 1273 K. The insulation performance is good in high temperature, which meets the need of the integrated sensors. And finally the composite insulation layer applies in thin film sensor on DZ4 alloy blade surface. The 30 μm thick Al2O3 composite insulating film is prepared on DZ4 alloy blade surface successfully. It is already the standard technical method of aircraft engine’s thin film sensor in our laboratory. |
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