Fabrication Of PdCr High Temperature Thin Film Strain Gauges

In the aviation turbine engine, turbine blades will subject to high temperature, strong vibration, thermal stress, high centrifugal force etc in the working state, due to the rapid rotation of the blade violent combustion and fuel.Turbine blade prone to damage and the whole engine failure for working long hours under such bad environment.Therefore, the health status of the turbine blades of real-time monitoring is an important significance for the study of aviation turbine engine. In this paper, we fabricate strain gauges directly onto the turbine blade surface by using the thin film deposition technology, forming a function / structure integration thin film strain gauge. The thin film strain gauges have several advantages: the thickness at the micro scale, do not damage the blade itself, fast response speed, do not affect the blade fluid characteristics, high sensitivity, good repeatability and isolation from high temperature, high pressure, air flow scouring.In this paper firstly, we prepared PdCr thin film by RF magnetron sputtering on Al2O3 substrates to study the influence of sputtering temperature, vacuum heat treatment process parameters on the properties of PdCr thin film micro structure and strain characteristics and electrical properties. The optimized process of PdCr thin film strain gauges are: sputtering power is 150 W, the substrate temperature is 400℃, the deposition time is 60 min, the film thickness is 1 μm, the flow rate of Ar is 35 sccm, the sputtering pressure is 0.5 Pa, in situ annealing temperature is 400 ℃ of 30 mins, the vacuum heat treatment temperature is 800 ℃ of 12 h. The process conditions of preparing PdCr film temperature coefficient of resistance(TCR) is 202 ppm/ ℃, the gauge factor(GF) is 1.87.Secondly, the layer structure and the process of reliable insulation on Nickel substrate at high temperatures were studied. The study found that the insulation layer having a crystalline YSZ/ amorphous YSZ/ amorphous Al2O3 structure has good high temperature insulation performance. The composite film insulating layer of insulating resistance is greater than 1.2 G? at room temperature and 150 K? at the high temperature of 800 ℃.It can meet the preparation of high temperature strain gauge insulation performance requirements.Finally, based on the optimization process of PdCr thin film strain gauge on the Al2O3 substrate, further research on the preparation of structure / function integration of PdCr high temperature thin film strain gauge on the nickel base high-temperature alloy surface wede studied. To increase the adhesive strength between of strain gauge function layer and the metal substrate and achieve the electrical insulation, we successfully deposited NiCrAlY- rich Al- Al2O3 gradient transition layer, YSZ/Al2O3 insulating layer, and then the prepared PdCr thin functional layer, and the preparation of the Al2O3/ ZrO2 protective layer on the surface of nickel base superalloy. The PdCr high temperature thin film strain gauge which had multi-layered function and structure integrated film was prepared, and then the gauge factors were measured at different temperatures. The measured GFs are all about 2.1,the heat output is about 100 με/℃ from room temperature to 800 ℃.