Johanna Ekberg

EBSD Analysis and Assessment of Porosity in Thermal Barrier Coatings Produced by Axial Suspension Plasma Spraying (ASPS)

Axial suspension plasma spraying (ASPS) is a relatively new, innovative spraying technique which has produced thermal barrier coatings (TBCs) with attractive properties such as high durability and low thermal conductivity. Using a suspension, it is possible to spray with finer powder particles resulting in coatings that have a columnar microstructure and contain a wide range of pore sizes, both nm-and μm-sized pores. To optimize the thermal properties and to maintain them during service of the components, it will be important to design TBCs with optimal porosity. Hence, an important part in the assessment of ASPS coatings is therefore the characterization of the microstructure and how it is build up, and the determination of porosity. Both aspects are addressed by performing measurement on splats and ASPS-coating using electron backscatter diffraction (EBSD) technique and by measuring porosity by Mercury Intrusion Porosimetry (MIP).

Analysis of single splats produced by axial suspension plasma spraying

ABSTRACT Axial suspension plasma spraying (ASPS) is a relatively new, innovative technique with which microstructures have been produced that are similar to the ones produced by electron beam physical vapor deposition. They have a columnar structure and consist of nm- and µm-sized pores. However, so far the formation of the microstructure is not fully understood because fragmentation and vaporisation of the liquid significantly affects the deposition process. Analysis of single splats can provide important information on the phenomena controlling the coating formation process and the final coating properties. Therefore, the present study aims at providing first results of 8 wt-% yttria-stabilised zirconia single splats sprayed onto a steel substrate by use of ASPS. Scanning electron microscopy and atomic force microscopy have been used to characterise the splats with respect to appearance, shape, and size distribution.

Porosity measurements in suspension plasma sprayed YSZ coatings using NMR cryoporometry and X-ray microscopy

A large variety of coatings are used to protect structural engineering materials from corrosion, wear, and erosion, and to provide thermal insulation. In this work, yttria-stabilized zirconia coatings produced by suspension plasma spraying were investigated with respect to their microstructure and especially their porosity, as the porosity affects the thermal insulation of the underlying component. To determine porosity, pore size distribution, and pore shape, the coatings were investigated using novel advanced characterization techniques like NMR cryoporometry and X-ray microscopy. In general, the porosity is inhomogeneously distributed and the coatings showed a large variety of pore sizes ranging from a few nanometers to micrometers.