Direct-Deposited Thin-film Strain Gauges for High-temperature Applications

Abstract

Strain gauges play a major role in the mechanical monitoring of processes and sequences in production engineering. They are also used for condition monitoring of components for lifetime prediction and detection of critical load conditions. In this context, strain monitoring in the high-temperature range is particularly relevant for monitoring the mechanical loads of engines, turbines, pipelines or forming equipment, but also for load testing in the aerospace industry. Since conventional strain gauges reach their temperature limitsdue to their polymer-based substrate and the adhesive, direct-deposited polymer-free strain gauges thus enable precise measurement of themechanical loads acting on the workpiece. In this article, stainless-steel tensile specimens were sputter coated with alumina for insulation, thin-film Nickel-Chromium (NiCr)for the strain gauges with Tantalum as a high-temperature diffusion barrier and adhesion promoter and finally alumina as a protective layer. With a developed high-temperature contacting, a constant temperature coefficient of resistance of 31ppm/deg C and an increasing k-factor of 1.4 at room temperature and 1.8 at 515 deg C were measured.Finally, strain measurements at 515 deg C are shown with maximum deviations of 50 micrometer/m.