The impact testing is an efficient experimental method that enables the quantitative and qualitative determination of the fatigue resistance of mono- and multilayer coatings deposited on various substrates, which was not possible with the common testing methods previously available. In this paper the experimental assessment of the fatigue resistance of coatings working under cyclic loading conditions by means of the dynamic impact testing method is presented. The fatigue failure mode, such cohesive or adhesive, of the investigated coatings is determined using scanning electron and optical microscopy, as well as EDX analysis. Critical values of the stress components, responsible for distinctive fatigue failure modes of the coating substrate system are obtained and the fatigue limits of aluminide coatings are illustrated in simple diagrams containing the impact load versus the number of successive impacts that the examined aluminide-P91 system can withstand.

Slurry coatings have been used for the protection of gas turbine materials in power plants during the last years. These coatings can be applied by spaying, brushing or dipping. The main constituent elements are silicon, chromium, potassium, borium, carbon and zirconium. They are characterized by high hardness and very good resistance against corrosion, erosion, abrasive and adhesive wear. To guarantee the reliability of coated steam turbines components used in power plants, the lifetime assessment of the coatings and their failure prediction become very important. Microhardness, scratch, adhesion and pin-on-disk sliding tests are commonly used for rapid evaluation of the mechanical properties of these coatings [F. Loeffler: Thin Solid Films, Vol. 339 (1999), p. 181]. However, the above testing methods do not model the dynamic cyclic fatigue. In this paper we evaluate the fatigue resistance of slurry coatings working under cyclic loading conditions by the impact testing method. The coating failure mode and its extent were assessed by SEM observations and EDX analysis. From the experimental results it was concluded that the Si,Cr,O,B,C coatings deposited on P91 steel substrate showed an improved fatigue strength compared to that of Si,Cr,O deposited on the same substrate.

Interactions between solid materials and liquid aluminum lead to a dissolution of solid elements into aluminum, which in turn results in a subsequent growth of intermetallic and intermediate phases. It was established that the growth of the intermetallic phases could be governed by chemical reactions at the interfaces and by interdiffusion of the reacting elements through the different phases. Dissolution on the other hand mainly depends on thermodynamic conditions, experimental parameters such as temperature, stirring time, and reacting holding time and on the degree of the saturation of aluminum as well as on the chemical composition of the solid materials in the reaction zone. The above-mentioned factors play also an important role in the formation of the different phases during dissolution. Nevertheless, a non-uniform distribution of the solute elements may causes a local concentration of these elements into the liquid aluminum, which practically delays the process or alters the equilibrium of the growth of the phases. Thus it is crucial to control the dissolution conditions so that the instabilities induced at the solid materials/aluminum interface are limited. The main objective of this study was to investigate both the formation of intermetallic and intermediate phases in the reaction zone and to examine the development of the diffusion structures of pure aluminum reinforced with TiB particles and to investigate the mechanical properties of the as-produced composite materials.