High Temperature Thin Film Insulator And Its Application In Thin Film Sensors On Superalloy Substrate

The development of aviation industry promotes the development of the design of jet aircraft and space-based engines.As the core part of the engine,the turbine blades have become the focus of the research.Because the blades working in harsh environment with high pressure,high temperature and high gas flow,it is important to monitor strain,temperature and heat flux with various of sensors for its safety and reliability.Thin film sensors are thought to be a superior choice compared to conventional wire and foil sensors because they allow the nonintrusive in-situ measurement of charateristics of engine components at high temperature.Considering turbine engine blades and vanes are usually made of conductive nickel-based superalloy,a good high temperature insulator between the sensor and the substrate is required.Therefore,the fabrication of the stable high temperature insulation layer is very important for high tempreaure sensors.However,in order to make full use of the advantages of the thin film sensors,the insulation layer as thin as possible is necessary.Among a variety of insulating materials,Al₂O₃ shows excellent insulation properties at high temperature.In this work,Al₂O₃ thin films were prepared by Dual Ion Beam Sputtering Deposition?DIBSD?.The films were characterized and tested at high temperature.Thin film sensors were fabricated on nickel-based superaloy substrates,which verified the good insulating properities of the DIBSD Al₂O₃ thin film insulator.The experimental parameters were optimized by orthogonal experiment.The stress analysis revealed that there is compressive stress in the DIBSD Al₂O₃ film and it can be reduced by setting and thickening.The microstructure characterization of the thin film shows that it has smooth,dense and compact microstructure and free of microcracks.The film was nearly stoichiometric Al₂O₃.The insulating properties of the Al₂O₃ thin film insulator sputtered with an oxygen partial pressure of 18%and with a thickness of 4?m are better than that of other film deposited under the same condition,respectively.High temperature tests revealed that the vertical electrical resistance of the thin film insulator kept 10⁶??cm on Pt-coated aluminum ceramic substrates and 10⁵??cm on superallpy substrates,respectively at 1000?.The Al₂O₃ insulator remains good insulating properties even after 5thermal cycles.The resistance temperature detectors fabricated on ceramic substrates and superalloy substretes showed good linear relations as high as 1000?.In order to further examine the high temperature insulation property of Al₂O₃ thin films,the ITO thin film strain gauge was fabricated by RF magnetron suputtering both on nickel-based superalloy and ceramic substrate.It was found that the gauge factor of the ITO strain gauge at room temperature increases with the increasing of oxygen flow and it was measured to be 0.59 at the oxygen flow of 20 sccm.High temperature tests revealed that the ITO strain gauge had different temperature coefficient of resistance?TCR?in different temperature ranges.In the temperature range from room temperature to 400?the sensor has a large negative TCR and it turned to be positive in the temperature range of 400?-600?.However,when the temperature increased from 600?to 900?the TCR become negative again.The TCR of the ITO thin film strain gauge fabricated on superalloy substrates have the same trend,which demonstrate that the DIBSD Al₂O₃ thin film has an excellent insulation property at temperature as high as 1000?.