In rocket engine combustion chambers the cooling channels are subjected to extremely high temperatures and environmental attack. Because of the good heat conduction the inner combustion liner is made of copper. Thermal and environmental protection can be provided by Thermal Barrier Coating Systems. The performance of an APS-sprayed standard coating system for nickel based substrates (NiCrAlY and YPSZ) on copper substrates is investigated. Because mechanical and thermal properties (e.g. the coefficients of thermal expansion) of the two substrates are different, known failure mechanisms for nickel based substrates can not be directly transferred to the new application. Thermal cycling and laser shock testing is performed to identify possible failure mechanisms. The laser shock setup consists of a high-power diode laser (3kW) and realizes surface temperatures of up to 1500°C. Furthermore, it is possible to realize high thermal gradients inside the specimen, similar to those in real service. Delamination of the thermal barrier coating at the interface between bond coat and substrate is observed. Usually, this interface is not failing in standard applications, which gives an important hint for further research. Furthermore, FEM analysis confirms that stresses are maximal at this interface.

Thermal barrier coating systems are used to enhance the temperature resistance of hot section components in gas turbines. The coatings protect the underlying nickel based components and consist of the bond coat (BC) the thermal barrier coating (TBC) and a thermally grown oxide (TGO) between the BC and TBC. The coating systems fail in service at or near the TBC/TGO interface. To study the failure mechanisms a simplified coating system is introduced which consists of a MCrAlY bond-coat material as the substrate, a TGO, and a yttria-stabilised zirconia TBC as a topcoat. The TBC is applied by atmospheric plasma spraying on top of specimens with defined roughness profiles, manufactured by a micromachining process. The main advantage of micro-machining is a defined interfacial roughness between the TBC and the BC in contrast to sandblasted specimens. Furthermore, a FEM simulation of the coating system was developed which approximates the interface by sinusoidal functions. This simplified model system and additional FEM calculations show the influence of varying the interfacial roughness between the BC and the TBC.

The investigation of the splashing and spreading behaviour of an impacting powder particle during the plasma spraying process is a field of research often performed with the help of simulations. To simulate thermal sprayed coatings at large scale, the Monte Carlo method is a useful technology. In the Monte Carlo model presented in this manuscript, spreading starts from the particle impact point and continues over the coating so that the behaviour at steps or other surface structures can be taken into account. The discretisation of the model is only lateral so that the thickness of the coating perpendicular to the substrate can take arbitrary values. The rules for particle spreading and deposition used in the Monte Carlo model are derived from a fluid dynamics model. For a two-dimensional simulation the Monte Carlo results provides good agreement with the fluid dynamics results.

The behaviour of plasma sprayed powder particles at impact is not adequately understood so that the microstructure of thermal barrier coatings cannot be predicted with the required accuracy. This is due to the complexity of the spraying process in which the shape of the impacting particles is influenced by the spraying conditions and the structure of the previously formed parts of the coating. In this paper we present some techniques to improve the understanding of coating formation. We investigate the impact of a single molten powder particle on a surface by performing splat tests, measuring the particle’s temperature, velocity, and diameter at the appropriate stand-off distance before the spraying process starts. The measured values are assigned to the splats. SEM-images of the splats are analysed by means of a image analysis algorithm. Thus we are able to evaluate the influence of particle properties on the splat shape. In order to get a better understanding of the mechanism of coating build-up, a three-dimensional series of cross sections is created. With this kind of examination the shape of splats can be characterised in three dimensions.

For 20 years now, the HVOF-method has been an industrially-established process for the application of hard-metal coatings to prevent wear phenomena from happening. A successful application combines the typical process parameters, conditions of materials and, above all, constructive frame conditions. In the following, we will present investigations for coating uneven outlines/contours such as edges, cavities or uneven surfaces. Furthermore, constructive frame conditions will be deduced from these and compared to our practical experience. The distribution of the layer thickness and its accessibility with the spray jet will be discussed as well. Here, we will have a closer look on which mechanical properties the basic substance has regarding hardness