Thermally matched multilayer ceramic composite insulating layers for high-temperature thick/thin-film sensors on nickel-based superalloy

Abstract

Thick/thin-film sensors are used for health monitoring of components such as aero-engines, which are mainly cast from electrically conductive nickel-based superalloys. It is necessary to prepare an insulating layer between the nickel-based superalloys and the thick/thin film sensor. For this purpose, a thermally matched multilayer ceramic composite insulating layers for thick/thin-film sensors have been designed. Three dielectric pastes with coefficients of thermal expansion similar to those of the metal substrate and Pt/Rh–Pt thick-film thermocouples were prepared on nickel-based superalloys by screen printing technique. Problems regarding the bonding strength of the insulating layers were solved, which improved the insulating properties. The microstructural characteristics of the insulating layers were characterized by scanning electron microscopy, and their insulation resistance at high temperatures was tested. The results show that the insulation resistance of insulating layers is increased by a factor of about 10 in this paper compared to the insulation resistance of insulating layers prepared by sputtering and other techniques in previous articles. When the temperature is 800 °C, the resistance value of the samples reaches 30.47 MΩ. It is noteworthy that the insulation resistance is still higher than 21 MΩ after annealing at 800 °C for 10 h. Moreover, the insulating coating survived thermal shock tests without cracking or delaminating. A S-type thermocouple is prepared on the insulating layers to verify its high-temperature electrical insulation performance. Test results show that the output voltage of the S-type thermocouple had a high linearity with an average Seebeck coefficient of 10.5 μV/°C during the temperature range of 200–1000 °C. Experiments show that the S-type thermocouple works stably at high temperatures and thermally matched multilayer composite insulation layers have good insulating properties.