Thermal History Coatings: Influence of Atmospheric Plasma Spray Parameters on Performance

Abstract

Thermal history coatings (THCs) provide a novel method for measuring temperature profiles in the 900–1600 °C range. Given the steadily increasing firing temperatures in turbomachinery, it is crucial to understand temperature distribution across the majority of a component surface (>80%) to verify the design and component durability. This new temperature profiling capability records the past maximum exposure temperature in such a way that it can be determined once the component has already cooled down. THCs are comprised of oxide ceramics deposited via atmospheric plasma spraying (APS) to create a robust coating. APS deposition employs several variable parameters; spray settings such as gun power, gas flow, or scan rate can affect the particle exposure and thus the microstructure of the coating and its temperature sensing performance. This work shows, for the first time, the influence of APS parameters on luminescent measurements due to changes in the material microstructure. This enabled optimization of the thermal history coatings sensing performance. Extensive calibration data were used to develop a new model to relate the APS spray parameters to the luminescent properties in the as-deposited condition and consequent performance as a temperature sensor. The powder composition and the power and gas flow used during deposition were found to be the most influential parameters. The model identified the optimum spray parameters and was used to demonstrate THCs can achieve measurements in excess of 1600 °C.