Laser deposited high temperature thin film sensors for gas turbines

Abstract

Purpose Accurate measurements of the temperature distributions in hot section components are indispensable for the prognostic and health management of gas turbines. Thin film thermocouple (TFTC) sensors, directly fabricated on the surface of a component, add negligible mass and create little or no disturbance to airflow, and therefore, can provide accurate measurements of fast temperature fluctuations of gas turbines. The purpose of this paper is to evaluate TFTC sensors fabricated by combining pulsed laser deposition (PLD) and micromachining techniques (LM). Design/methodology/approach The “dry” PLD/LM fabrication approach allows for excellent control of the chemical composition and physical characteristics of the constituent layers and their interfaces, thus achieving good adhesion of the layers to the substrate. Findings The results of thermal cyclic durability testing of the fabricated TFTC sensors demonstrated that the proposed PLD-based approach can be used to fabricate sensors that are fully functional at temperatures up to 750°C. Analyses of the sensor performance during durability testing revealed: the existence of a threshold temperature below which accurate temperature measurements were achieved; an abrupt drop in the sensor output occurring when the sensor temperature exceeded the threshold value, with a fast recovery of the sensor output once the temperature was reduced below the threshold level; and sensor “training” capable of increasing the threshold value of the TFTC through its exposure to above-the-threshold temperatures. Originality/value The work is the first time to demonstrate that simple PLD and LM processes can be used to fabricate TFTC that are fully functional at temperatures up to 750°C.