Study On Flexible Film Strain Gauge For High Temperature Applications

In the field of Aeronautics and Astronautics,aerospace devices generally work in high temperature,high pressure,strong vibration,heavy oil and other harsh environments.The aerospace devices are easy to cause internal damage due to the long-time working in this environment,which makes the whole spacecraft failure.Therefore,the real-time health detection of aerospace devices becomes very important.At present,the important way to solve this problem is the thin film strain gauge,which uses the thin film deposition method to deposit the strain sensitive material on the substrate surface,and reflects the current stress of the device to be tested through the change of resistance.The substrate of traditional thin film strain gauge is usually rigid metal material substrate or organic polymer flexible substrate.These two kinds of thin film strain gauge can't work in curved uneven surface and high temperature environment,so it is very urgent to meet the requirements of high temperature strain gauge for curved surface environment test.In this paper,aiming at the problems existing in traditional thin film strain gauge,the development of thin film strain gauge on flexible Hastelloy alloy substrate is carried out.Firstly,two kinds of strain sensitive materials NiCr and PdCr were prepared on Si/SiO₂ substrates by RF magnetron sputtering.The effects of sputtering pressure and substrate temperature on the microstructure and electrical properties of the two kinds of strain sensitive materials were studied.The results show that the best preparation conditions of NiCr are:background vacuum is 5×10^-5 Pa,sputtering power is 70 W,sputtering pressure is 0.2 Pa,substrate temperature is 400?,annealing temperature is500?,annealing time is 120 min,Ar gas flow is 45 sccm,target base distance is 80mm.The temperature coefficient of resistance of NiCr film prepared by this process is 131ppm/?.The optimum process conditions for the preparation of PdCr thin films are:background vacuum is 5×10^-5 Pa,sputtering power is 70 W,sputtering pressure is 0.25Pa,substrate temperature is 400?,annealing temperature is 500?,annealing time is 120min,Ar gas flow is 45sccm,target base distance is 80mm.The temperature coefficient of resistance of PdCr film prepared by this process is 154ppm/?.After obtaining the best preparation conditions,Y₂O₃ transition layer,AlNO-Al₂O₃insulating layer,strain functional layer and Al₂O₃ protective layer were prepared on the flexible Hastelloy alloy.The strain functional layer was prepared by the best preparation technology,and the second mask method was used to figure the variable functional layer.Finally,NiCr and PdCr thin film strain gauges with high softness are prepared and calibrated at different temperatures.The gauge factor of NiCr is more than 3 at 400?.The gauge factor of PdCr increases from 1.78 to 2.12 at room temperature to 550?.The repeatability of PdCr film strain gauge is better than that of NiCr film strain gauge.The NiCr flexible film strain gauge and PdCr flexible film strain gauge obtained from the experiment provide a new means for high temperature strain measurement.It is of great significance to the development of China's aerospace industry.