Evaluation of colour changes of the blade surface after exposure to high temperature

The article presents the results of research on the effect of temperature, including temperatures outside the nominal operating range, on the condition of the protective layer (coating) of aircraft engine gas turbine blades. The experiment focused on the effect of temperature, omitting the influence of the chemical effect of the working medium (exhaust gas). Certain relationships were demonstrated between the recorded surface colours of the blades and changes in the chemical composition, coating thickness and roughness of the surface layer. An analysis of surface colours was carried out in the L*a*b* colour space. It allowed determining the colour relations (quantitative assessment) between the recorded surfaces. In addition, the chromatic components a* and b* were associated with the change in coating thickness. The obtained results indicate the great potential of this space in diagnosing the technical condition of blades based on the analysis of their colour.