Investigation of the Relationship between Degradation of the Coating of Gas Turbine Blades and Its Surface Color

Abstract

This article presents issues concerning the relationship between the degradation of the coating of gas turbine blades and changes in the color of its surface. Conclusions were preceded by the determination of parameters characterizing changes in the technical condition of protective coatings made based on a metallographic examination that defined the morphological modifications of the microstructure of the coating, chemical composition of oxides, and roughness parameters. It has been shown that an increased operating time causes parameters that characterize the condition of the blades to deteriorate significantly. Results of material tests were compared with those of blade surface color analyses performed using a videoscope. Image data were represented in two color models, i.e., RGB and L*a*b* with significant differences being observed between parameters in both representations. The study results demonstrated a relationship between the coating degradation degree and changes in the color of the blade’s surface. Among others, this approach may be used as a tool to assess the condition of turbine blades as well as entire gas turbines.

Health and Durability of Protective and Thermal Barrier Coatings Monitored in Service by Visual Inspection

“…HPT blades have an internal cooling system without film cooling. They are made of ZhS26 or ZhS32 nickel-based alloys with directional solidification [29,57,58].…”

“…In our previous paper [56], HPT blade health was monitored in service via borescope inspection, and the gradual degradation of the original coating caused by overheating, oxidation and corrosion was presented in macroscale. Bogdan et al studied the microstucture of five blades with varying degrees of wear [42,57]. They observed coating wear and its gradual degradation.…”

“…Small dimensions of the optical system and limitations in the optimal placing of the sensing head cause significant image distortion. In our previous work [57], MATLAB Computer Vision Toolbox was used to calibrate the borescope system. The determined parameters of the optical system were used for correcting lens distortion, centering the view and automatic image processing.…”

High-Temperature Materials for Complex Components in Ammonia/Hydrogen Gas Turbines: A Critical Review

“…Energy-dispersive X-ray spectroscopy (EDS) is a technique that is used to obtain the chemical composition of materials. In the case of gas turbine materials and blades, EDS analysis can be used to identify the presence of impurities or degradation products, enabling the identification of any defects or degradation mechanisms [222]. • X-ray diffraction (XRD) is a technique that is used to investigate the crystal structure of materials.…”

Special Issue “Corrosion Resistance of Alloy and Coating Materials”

“…The innovative research methodology was also included in the scope of the presented works. The relationship between the degradation of the coating of gas turbine blades and its surface color was discussed in the paper [ 15 ]. The proposed approach significantly expands the possibilities of the nondestructive appraisal of gas turbine blades, especially in assessing their technical state without the need for their disassembly.…”