Thermal history paints - principles and progress

Temperature is a critical parameter in many engineering applications, particularly in gas turbines, to avoid overheating of critical components and improve the efficiency of operation. Effective thermal management requires accurate temperature profiles in key locations; however, performing these measurements during operation is practically challenging, sometimes impossible due to inaccessibility of the components. A desirable alternative would be to record the exposure temperature in such a way that it can be determined later, off-line. Of the currently available off-line methods, Thermal Paints are arguably the most popular, however, are highly toxic in nature and come with a range of technical disadvantages such as subjective readout and limited durability. A novel, alternative measurement technique has been proposed by the authors and is under development. This technique uses phosphorescent sensor materials which undergo permanent changes with thermal exposure. The changes manifest in the phosphorescent properties of the material, such as the decay time. The technique has a plurality of technical and practical advantages over existing measurement methods. A major benefit is the automated electronic readout of the coating which eliminates the need to have a colour-trained operator and thus increases the speed of interpretation. This paper focuses on the progress made in the development of Thermal History Paints. The repeatability and error of measurements made using a purpose built electronic hand-held mobile device are discussed to demonstrate the practical application of the technology. Further a robust Thermal History Coating, based on Thermal Barrier Coating architecture, is introduced demonstrating the capability of the coating to withstand long term exposures and harsh environments. A comparison between a comm