Comparative Study of the Heat Resistances of Protective Coatings

Modern gas turbine engines operate under changing temperature loads; therefore, one of the important characteristics of the protective coatings of turbine blades is their high resistance to the appearance and development of cracks under mechanical and thermal loads. The effective internal heat removal systems used to cool turbine blades lead to an increase in their thermal stresses. Currently, thermal fatigue cracks are among the common defects in the protective coatings of turbine blades. The heat resistance of the coatings at high temperatures is determined by the following three factors: the shape of the part onto which a coating is applied, the coating thickness, and the phase composition of the surface layers or the maximum aluminum content in a coating. Therefore, when a protective coating is chosen under these operating conditions, it is important to know the influence of these factors on the heat resistance of a coating. In this work, we compare the cracking resistances of various coatings during cyclic temperature changes. The heat resistances of the coatings are found to depend on the method of application and their phase-structural state. The revealed mechanism of formation and propagation of thermal fatigue cracks depending on the phase composition of an initial coating is especially important. The life of the protective coatings under cyclic temperature changes is shown to depend on the chemical composition of a coating and the method of its formation. The dependence of formation of thermal fatigue cracks on samples with the coatings under study on the number of temperature change cycles has been revealed.