Devolopment of thin film temperature sensors for high performance turbo jet engines

Abstract

The introduction of ceramic thermal barrier coatings, then monolithic ceramic blades and finally blades made from ceramic-metal composites are expected to have dramatic effects on the operating temperatures of gas turbines. Successful functioning of these components in the hostile environment of a gas turbine depends partly on the accurate measurement of their surface temperature, and for this, the development of appropriate technology is needed. This paper deals with the two phase research program started by us at UCLA on the development of Pt/Pt+Rh thin film thermocouples on nickel based superalloys and monolithic ceramic type blades and vanes. In the case of super-alloy substrates, the thermocouple consists of 10 micron thick Pt and Pt + 10% Rh thin film elements deposited on the insulating surface of the blades and vanes. The insulator is developed by a combination of treatments given to the coated blade. Thermocouples, stable up to 50 hrs. in an oxyacetylene flame (1050°C) with less than 5 percent drift in temperature, have been fabricated. Pt and Pt + Rh thin films are currently being deposited on sintered SiC and Si₃N₄ substrates. Some results of thermo-emf measurements for thermocouples deposited on Si₃N₄ blades are also reported here, especially in regard to emf-drift due to Pt-Si interdiffusion and oxidation of rhodium.