High‐temperature behavior of different coatings in high‐performance gas turbines and in laboratory tests

Abstract

Turbine blades of advanced engines are often subject to a surface attack caused by oxidation or hot corrosion. Typical features of the different modes of high‐temperature surface attack are presented using results of failure analysis of turbine parts and of laboratory experiments. At very high temperatures, interactions take place between the coatings, which are indispensable in this temperature range, and the base metal. Some examples are described that have been gained from cyclic oxidation tests with a nickel‐base single‐crystal alloy and different types of coatings. The development of a broad diffusion zone and the depletion of β phase of the coatings indicate that interdiffusion plays an important role in determining the coating life. In a particular temperature range platelike phases precipitate in the matrix close to the coating. Kirkendall porosity, which frequently occurs at the coating substrate interface at very high temperatures, can markedly reduce the adhesive strength. The behavior of coated parts under mechanical loading is influenced by the coating–substrate combination. Some examples are shown describing creep and thermal fatigue properties of coated components.