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 Barriers Coatings (TBC) are mass-produced in several industrial fields: aeronautic, automotive or energetic industries. All production requires the same constant level of fest and reproducible quality control at the lowest cost. The metallographic process is the primary way to evaluate thermally sprayed coatings but it must be both highly very repeatable and fast, especially when metallography is used to keep the production at a constant level. Therefore the management and the organization of a metallographic laboratory is of prime importance in order to reduce the cost and to provide a quality structure. The present approach to the whole chain of characterization is based on the user's point of view. Generally speaking, metallographic control of widely used parts often seems to be considered to be an uninteresting and obtuse subject, since it has been in practice for so long. Despite the lack of the prestige associated with the subject, optimization of an appraisal post can provide very concrete and more importantly profitable, results.