The purpose of this work is a general assessment of the evolution of the porosity of a thermal barrier coating (PSZ : Partially Stabilized Zirconia with 7% wt yttria) used as an SOFC electrolyte sprayed by a High Power Plasma system Plazjet using commercial powders. The properties of these coatings are investigated using a microstructural and a physical approach. The different steps concern : - the optimisation of the spraying parameters of the Plazjet gun, in order to obtain either very dense, or porous top coat microstructure. We focused on parameters such as the gun (external, or step) or the morphology of the powder. The use of a strict methodology to analyze the results. Characteristics obtained by various measures, qualitative and quantitative, are compared and discussed.

The Plazjet system usually works with a binary gas mixture of nitrogen and hydrogen for the deposition of a thick TBC (NiCrAlY as a bond coat and Zirconia as a top coat). In order to improve the performances of our spraying device and ensure good quality coating, different experiments were conducted. The substitution of N 2 or the classical binary mixture N 2 /H 2 respectively by a binary N 2 /He, and a ternary gas composition N 2 /H 2 /He leads to an evolution of the deposition efficiency and quality coating. In order to optimise the various ratio in the gas mixture, the evolution of experimental parameters such as voltage were analysed.

Thermal spray usually involves high temperatures in short times. This phenomenon is enhanced with the use of an HPPS system (Plazjet from Tafa). To spray a Zirconia coating, high powers are necessary such as 200 kW providing for the substrate an important increase in the surface temperature. Furthermore, the good quality of a thermal spray coating results in the low surface roughness, a satisfactory microstructure cohesion, a minimal distortion of the part when spraying on large sheets with a thick thermal barrier coating. Cooling with compressed air is widely used but other solutions are studied concurrently; CO 2 , nitrogen, and air; these gas are tested in different conditions of pressure and flow. Some improvements in terms of temperature in the coating and roughness have been found.

Substrates protected by thermal spray coatings are usually found intact after use, making them viable candidates for recycling and reuse. The key is to remove the coating without damaging the component. This requires a process that minimizes the development of residual stresses and the associated distortion. The purpose of this work is to determine the optimal descaling technique for Ni-base sheets with a thermal barrier coating. Test specimens were produced following industry procedures. Thin sheets (<3 mm) of Ni-base superalloy were plasma sprayed with a NiCrAlY bond coat and a Y203-stabilized ZrO2 topcoat. The coating layers were then removed using different methods, including pickling, shot blasting, and water jet descaling, and the substrates were assessed based on X-ray diffraction and chord width measurements. The findings of the study show that water jetting removes all surface materials, particularly the bond coat, without damaging the underlying surface. It also produces the least amount of stress and deformation and is relatively easy to automate.

Thermal Barrier Coatings (TBCs) are commonly used in aeronautics for both thermal and corrosion resistance. The PlazJet is a high power plasma torch designed by TAFA. Optimization of plasma sprayed coatings needs to realize a lot of experiments considering the large number of process parameters, so systematic experimentation becomes very long and expensive. Optimization methods such as the Taguchi methodology have been commonly used in the Thermal Spray industry. This paper presents an optimization of TBC sprayed by PlazJet according to the Taguchi method. It discusses coating properties such as application efficiency, thickness, density, surface shape, and adhesion in order to correlate these with variations in the process parameters. The paper also presents optimized parameters for this special application. Paper includes a German-language abstract.

This paper presents the comparison of a TBC coating obtained by a conventional and a high power plasma system. It aims to analyze the benefits of the Plazjet in terms of high productivity and high quality. The first part of this paper consists of a technical review of the spraying torches: a classical 40 kW APS is compared with the 250 kW HPPS Plazjet. The second part consists of a description of the spraying tests conditions: material substrate, powders, and qualitative and quantitative characteristics of the coatings. An additional study of the economic features is conducted to analyze the industrial point of view. Paper includes a German-language abstract.

When spraying is conducted in the ambient atmosphere, the entrainment of air cools down the plasma jet and affects its expansion. It may also cause the oxidation or the chemical decomposition of the sprayed materials. Inert Plasma Spraying (IPS), generally conducted in argon atmospheres, prevents these phenomena. However, the main drawbacks of IPS in comparison with air plasma spraying are the capital and apparating costs. To reduce the latter by 25 to 30%, nitrogen atmospheres may be used as a substitute for the conventional argon atmosphere. This paper presents a study in which titanium carbide and niobium powders were sprayed in argon and nitrogen atmospheres. Cryogenic cooling of the substrate was used during the spray process. This helps to maintain a low temperature in the chamber, produces thick coatings and allows the use of substrate materials that are sensitive to heat. The adhesion, roughness and microstructure of the coatings produced in both atmospheres are compared as well as their nitrogen content.