No abstract

Nowadays, wire-arc spraying of chromium steel has gained an important market share for corrosion and wear protection applications. However, detailed studies are the basis for further process optimization. In order to optimize the process parameters and to evaluate the effects of the spray parameters DoE-based experiments had been carried out with high-speed camera shoots. In this article, the effects of spray current, voltage, and atomizing gas pressure on the particle jet properties, mean particle velocity and mean particle temperature and plume width on X46Cr13 wire are presented using an online process monitoring device. Moreover, the properties of the coatings concerning the morphology, composition and phase formation were subject of the investigations using SEM, EDX, and XRD-analysis. These deep investigations allow a defined verification of the influence of process parameters on spray plume and coating properties and are the basis for further process optimization.

Materials in the system

Laser beam welding is a field of growing importance to the industry. As a result of extensive and continuous development of laser beam technology, pulsed Nd:YAG laser beam sources have been introduced. Pulsed laser welding offers the advantage of very low heat input to the workpiece, resulting in low distortion and the ability to join heat sensitive components. Further improvements to the method consider pulse shape modulation in Nd:YAG laser beam sources resulting in improved weld pool dynamics. Nd:YAG laser beam welding with pulse shape modulation is studied both experimentally and theoretically. Observational results on the interaction between time-dependent heat fluxes and flows in the weld pool as well as on solidification of the molten material are presented. In welds produced with modulated laser beam pulse shape, improved material flow and finer microstructure have been observed. Using an axisymmetric 2D model for heat transfer coupled with surface tension driven flow of molten metals undergoing solid-liquid and evaporation phase transitions in the weld pool, it is shown that the time modulation of the pulse power influences the melting front and flow velocity which together with the predicted undercooling may explain the fine-grain structure of the resolidified welds that have no cracks inside.

The industrial application of APS sprayed YPSZ coatings for thermal insulation is established in several branches. As the main potential to increase the efficiency of combustion processes is thermal efficiency and the state‐of‐the‐art systems are limited to surface temperatures below 1200°C for long term applications, there is interest in concepts, that allow an increase of the process temperature. Ceria and ceria based ceramics show an outstanding potential for use at temperatures exceeding 1200°C. A triple‐layer thermal barrier system in consideration of the established system – MCrAlY bond coat and YPSZ – and an additional ceria based top coating are investigated. TBC systems with two different ceria powders are produced by APS and HVOF spraying and evaluated with concern to the microstructure, bond strength, thermal shock behaviour and long term compatibility of the constituents. HVOF sprayed coatings contain more oxygen, are more dense than APS sprayed coatings and do not show segmentation due to cracks perpendicular to the surface. APS sprayed pure ceria coatings show a columnar morphology inside single splats forming the coating. The bond between YPSZ and ceria and the total bond strength of the thermal barrier system exceeds the cohesion inside the ceria coating. The thermal shock resistance of ceria coatings with high silica and sulphur content is low. Long term sintering investigations prove the compatibility of ceria and YPSZ at 1150°C.