Comparative Heat-Resistance Investigation of Protective Coatings

Abstract

Since modern gas turbine engines operate under changing temperature load conditions, one of the important characteristics of the protective coatings on 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 stress. Currently, the cracks induced by thermal fatigue are one of the common defects in the protective coatings on 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 the coating. Therefore, when a protective coating is chosen under specific operating conditions, it is important to know the influence of these factors on the heat resistance of the coating. In this work, we compare various coatings in terms of their resistance to cracking during cyclic temperature changes. The dependence of the heat resistance of the coatings on the method of their application and the phase-structural state is established. The revealed mechanism of thermal-fatigue crack formation and propagation as a function of the phase composition of the initial coating is especially valuable. The life of the protective coatings under cyclic temperature changes is shown to depend on the chemical composition of the 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 is found.