Development of High-Temperature Wire-Grid Thin Film Strain Gauges

Aero-engine turbine stator blades are often used in harsh environments with high temperatures and high pressure and are prone to fatigue fractures. Real-time and accurate monitoring of blade surface stress and strain is critical to ensure safe operation. In this study, thin-film strain gauges (TFSGs) that can be used in high-temperature environments above 1000 °C were designed and fabricated using a PtRh6 thin film as the sensitive material. The hysteresis effect of the stress transfer upon establishing a thermo-mechanical coupling finite element model of the Inconel718 high-temperature nickel-based alloy equal-strength beam PtRh6 TFSGs was analyzed and the optimal combination of thin-film thickness and longitudinal grid length of wire-grid TFSGs was determined. In order to solve the problem of high-temperature insulation, the insulating properties of a single-layer Al₂O₃ insulating film, a single-layer ZrO₂ insulating film, a double-layer Al₂O₃/ZrO₂ composite insulating film, and a four-layer Al₂O₃/ZrO₂/Al₂O₃/ZrO₂ composite insulating film at high temperature were compared and studied using scanning electron microscopy to analyze the microscopic morphology and composition of the four insulating film structures. The results showed that the four-layer Al₂O₃/ZrO₂/Al₂O₃/ZrO₂ composite insulating film had the best insulating properties at high temperatures. On this basis, an Al₂O₃/ZrO₂/Al₂O₃/ZrO₂ composite insulating film, PtRh6 sensitive layer, and Al₂O₃ protective film were sequentially deposited on a high-temperature nickel-based alloy equal-strength beam using DC pulsed magnetron sputtering technology to obtain an Inconel718 high-temperature nickel-based alloy equal-strength beam PtRh6 TFSG. Its gauge factor (GF) and temperature coefficient of resistance (TCR) were calibrated, and the results showed that the sensor could be used in harsh environments of 1000 °C. The above results provide new ideas for measuring stress and strain in aerospace under high-temperature and high-pressure environments.