The ongoing drive to improve efficiency and thrust of high performance gas turbines has led to the integration of thermal barrier coatings. These coatings enable the components to operate at higher temperatures whilst maintaining economic service life. It is recognised that further increases in operating temperature are the primary route to achieving higher performance. As such the thermal barrier coatings will need to become prime reliant. Quantitative non-destructive methods are, therefore, required to evaluate the degradation of the coatings to improve lifing estimates and develop condition-based maintenance procedures. In certain operating regimes, particularly in environments with contaminated intake air, degradation of the coating can occur by gradual thinning from the surface leading to complete failure. Current inspection routines cannot identify these gradual degradation mechanisms. The introduction of small amounts of rare-earth oxides into the standard thermal barrier coating materials makes the coating phosphorescent. The dopant ions act as atomic scale sensors which can be interrogated non-destructively through their phosphorescent properties. The dopant ions can be introduced in distinct layers through the coating thickness as a means to detect gradual thinning. The first detailed characterisation of this technique has been conducted. The phosphorescence was imaged using standard instrumentation to provide a rapid quantitative assessment of the erosion damage. After image processing the thickness profile of the coating was reconstructed and correlates to two forms of validation measurements. Testing, on a thermal gradient rig and on an aeroengine test bed, has demonstrated that the sensor function can be introduced whilst maintaining the primary function of the coating.
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