Industrial Sensor TBCs: Studies on Temperature Detection and Durability

Abstract

This article describes recent developments of the thermal barrier sensor concept for non‐destructive evaluation (NDE) of thermal barrier coatings (TBCs) and on‐line condition monitoring in gas turbines. Increases in turbine entry temperature in pursuit of higher efficiency will make it necessary improve or upgrade current thermal protection systems in gas turbines. As these become critical to safe operation it will also be necessary to devise techniques for on‐line conditions monitoring and NDE. Thermal barrier sensor coatings, which consist of a ceramic doped with rare‐earth activator to provide luminescence, may be a possible solution. The thermo‐luminescent response of such materials has been shown to be suitable for surface and sub‐surface temperature measurement and possibly for material phase determination. Herein we describe a number of steps in the development of the sensor coating technology. For the first time sensor coatings have been successfully produced using a production standard air plasma spray (APS) process. Microscopic analysis of the coatings showed them to be similar to standard TBCs and thermal cycle testing of the coatings to destruction showed them to exhibit durability similar to that of standard TBCs suggesting that the addition of rare earth dopants to produce sensor coatings does not change the material structure or the longevity of coatings. Calibration of the coatings using the lifeteime decay response mode showed them to have a dynamic range for temperature measurement extending to just under 1000°C. However, it should be noted that newer compositions have been shown to respond up to 1300°C. Finally, a study of surface temperatures and film cooling has been conducted in a research combustor using APS sensor coatings and some preliminary results are presented.