Comparative Study of the Heat Resistance of Protective Coatings

Modern gas turbine engines operate under changing temperature loads; therefore, one of the important characteristics of the protective coatings used on turbine blades is their high resistance to the initiation and propagation of cracks under mechanical and thermal loads. The effective internal heat removal systems used in cooled turbine blades lead to an increase in their thermal intensity. Currently, thermal fatigue cracks are common defects found in the protective coatings used on turbine blades. The heat resistance of the coatings at high temperatures is determined by three factors: the shape of the part on which a coating is deposited, the coating thickness, and the phase composition of the surface layers or the maximum aluminum content in a coating. Therefore, when choosing a protective coating for these operating conditions, it is important to know the influence of these factors on the heat resistance of a coating. We perform a comparative study of the cracking resistance of various coatings under cyclic temperature changes. The dependence of the heat resistance of the coatings under study on their deposition method and phase-structural state is determined. The revealed mechanism of formation and propagation of thermal fatigue cracks as a function of the phase composition of the initial coating is particularly important. The life of 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 thermal fatigue crack formation on samples with the coatings under study on the number of temperature change cycles is found.