Issue 35

T. Sadowski et alii, Frattura ed Integrità Strutturale, 35 (2016) 492-499; DOI: 10.3221/IGF-ESIS.35.55 493 To prevent phenomena such as corrosion or thermal shocks, working surfaces of blades are covered by different types of ceramic protective coatings, i.e. Thermal Barrier Coatings (TBC) [3,5,6]. Industrial application found many types of layers obtained by a gas method, contact – gas method, PVD and others. These layers allow for considerable increase of the heat-resistance properties of the blade which is shown in the present paper. Using the thin ceramic layers we can get also extension of the exploitation time. T HE FACTORS INFLUENCING THE FATIGUE DURABILITY OF THE TURBINE BLADE he fatigue durability of the structural elements of the engine is influenced by: - structural factors, - applied technology for manufacturing, - exploitable conditions. Structural factors include: shape of the elements, their dimensions and local small initial micro-defects (micro-indentations or micro-notches). Manufacturing technology obeys: technological operations for production of the elements, applied processes for improvement of a superficial zone properties. Moreover, the state of the elements surface improved by galvanized covering, grinding and polishing is very important. The exploitable conditions are defined by loading spectrum, pauses of loadings, complexity of loads, the level of operational temperature and the presence of active corrosion environment. The superficial corrosion causes pitting formation and further local roughness. They act as local surface micro-cavities or micro-indentations. Depending on their quantity and dimensions, activity of these defects can be analysed as individual separated indentation (dilute defect density) or when their number is very high these micro-defects can interact (row of defects). Fig. 1 presents an image magnified under SEM in 2 characteristic places of the fatigue and corrosion wear blade: in half its height and in its bottom part. It should be noticed that the blade already reached suitable service life and was excluded from exploitation. The analysis of the state of these 2 points leads to formulation of the following conclusion: the bottom part of the blade is strongly subjected to erosion and corrosion due to the combustion gases. One can notice visible pitting and the micro-indentations. The indentations situated in the bottom part of the blade are the most dangerous, because during exploitation the local maximum of the von Misess stresses takes place. It results from bending of the blade during its work, see Fig. 2. Figure 1: Surface of the blade. Figure 2: Maximum of the von Misess stresses. Additionally, a chemical analysis was performed in several characteristic points of the blade in order to define proportional percentage of individual chemical elements. Their average content was showed in Fig. 3. Altogether 13 chemical elements were detected, from which Ni, Al and Mo are the elements entering composition of alloy from which the blade was made and their total weight content is the highest. The next chemical element is carbon and it T