Thermal history coatings: influence of atmospheric plasma spray parameters on performance

Firing temperatures in gas turbines have seen a steady increase over the years to allow for higher engine efficiencies and lower hazardous emission levels. Conversely, these harsh conditions severely challenge component lifetime, requiring a design trade-off. Thus, it is crucial to understand temperature distribution across most of a component surface (>80%) to verify the design and durability. While a range of temperature measurement techniques are available, these primarily focus on lower temperatures, exhibit low durability (thermal paints), require line of sight (pyrometers), are destructive (thermal crystals) and only provide point measurements (thermocouples).

To overcome this challenge, Thermal History Coatings (THCs) measure temperature profiles in the 900-1600°C range. This new temperature profiling capability records the past maximum exposure temperature; this is determined once the component has already cooled down.

THCs are oxide ceramics deposited via Atmospheric Plasma Spraying (APS). APS deposition employs several variable parameters, which can affect the material process and therefore its temperature sensing performance.

This paper shows, for the first time, the influence of APS parameters on luminescent measurements due to changes in the material microstructure. Extensive calibration data was used to develop a new model relating APS spray parameters to the luminescent properties and consequent performance as a temperature sensor. The model identified the optimum spray parameters and was used to demonstrate THCs can achieve measurements in excess of 1600°C.