Assessing the Condition of Gas Turbine Rotor Blades with the Optoelectronic and Thermographic Methods

Abstract

Gas turbines and their blades in particular might be damaged in the course of the aviation turbojet engine operation process. The degradation process of the blade microstructure is most evident from the change in the colour of its surface. This is assessed using the optoelectronic method. The article presents the concept of non-destructive methods, which are used to assess the degree of degradation of the alloy of a gas turbine blade. The proposed optoelectronic method is the basic method for the preliminary determination of color changes in the surface. Appropriate videoscopes or video-analyzers, capable of recording a test object in various electromagnetic wave ranges (infrared radiation, visible range), are used for this purpose. These preliminary results of the diagnosis make it possible to infer further studies of the blade. For accurate investigation of the state of the alloy microstructure, a non-destructive thermographic method (xenon flash pulsed thermography) was used. The results of studies of the degradation of the microstructure with the use of non-destructive methods were verified through the use of metallographic investigations. Appropriate metallographic specimens were created in order to recognize phase γ′ degradation (i.e., the phase strengthening the blade alloy). The results of the presented research allowed for an in-depth assessment of the degree of microstructure degradation of operated blades.

Electron Microscopy Characterization of the High Temperature Degradation of the Aluminide Layer on Turbine Blades Made of a Nickel Superalloy

“…The current paper demonstrates that with the exception of the formation of the alumina layer, all other occurring processes such as coarsening of the microstructure of the coatings, formation of pores, outward diffusion of Fe and Cr to the surface, degrade the insulation and protective properties of the heat-resistant coatings. The processes of the microstructure coarsening and the formation of pores have been reported in the past, as seen in, for example [ 25 , 30 ]. Two processes (outward diffusion of Fe and Cr to the surface, and the formation and subsequent coarsening of Fe-Cr particles on the surface of the alumina layer), to the best knowledge of the authors, have not so far received much attention.…”

“…At the same time, understanding the processes taking place in the coating during their exposure to high temperatures is of key importance in predicting the remaining time-of-life of the elements they are meant to protect, as well being essential to the development of Non-Destructive Testing (NDT) procedures for the evaluation of those components after they have been exposed to in-service conditions. One such procedure, based on the color analysis of the light reflected from the protective coating, has been put forward by M. Bogdan [ 28 , 29 , 30 ]. In order to strengthen the physical basis of this procedure, it is desirable to gain insight into the changes taking place in the outermost layers of the aluminide layer exposed to extreme heating.…”

Thermal Methods for Damage Evaluation of Metallic Materials

“…The condition of gas turbine rotor blades was assessed with the optoelectronic and thermographic methods in the work of Bogdan et al [4]. Metallographic investigations were carried out to verify the degradation of the microstructure.…”

Intelligent Thermal Imaging-Based Diagnostics of Turbojet Engines

“…These defects can be damage to the turbine blades, combustion chamber disturbance, disturbance to the homogeneous field of fuel burning, etc. [28].Aircraft engine diagnostics and health monitoring [29][30][31] can be divided into two basic processes: ground diagnostics and on-board diagnostics with their associated systems. On-board, or online, diagnostics involve the checking of engine components and thermodynamic processes during the operation of the engine [32].…”

“…These defects can be damage to the turbine blades, combustion chamber disturbance, disturbance to the homogeneous field of fuel burning, etc. [28].…”