Combining 3-D Printing and Magnetron Sputtering Technique for Fabricating High-Temperature AgPd Thick Film Strain Gauge

In the aerospace industry, there is significant interest in high-temperature thin/thick film strain gauges (TFSGs) that possess hot-end component health monitoring capabilities. However, 3-D printed TFSGs exhibit limited thermal stability, and the use of conventional thick-film encapsulation can significantly compromise the gauge factor (GF). Here, we deposited a sensitive layer using 3-D printing and then a protective layer using magnetron sputtering to complete the preparation of AgPd TFSG. Experimental confirmation showed that as the thickness of the protective layer increases, the GF of the TFSG decreases. The GF of AgPd TFSG at room temperature was 1.327 with a decay rate of only 1.4% when the protective layer was magnetron-sputtered yttria-stabilized zirconia (YSZ) with a thickness of $2 ~\mu \text{m}$ . The high-temperature test results showed that the AgPd TFSG had excellent repeatability in a wide temperature range of 100 °C–800 °C, with a temperature coefficient of resistance (TCR) of 181 ppm/°C. In addition, the resistance drift rate of unencapsulated TFSG was 0.29%/h for 8 h at 800 °C, and 0.04%/h for the TFSG with the YSZ protective layer. For strain measurement, the TFSG exhibited low mechanical hysteresis, excellent stability, and repeatability at room and elevated temperatures within $\pm 500 ~\mu \varepsilon $ . The obtained TFSG not only exhibited cyclic stability (3300 cycles) but also had an ultrafast response (384 ms). This new methodology presents an attractive route to prepare TFSGs with high thermal stability and low GF attenuation for in situ strain sensing of hot-end components.