Large (3 x 3 x 0.05 m 3 ) refractory pieces (as the ones used for examples in smelters or incinerators) do not sustain regular glazing in a kiln, mostly due to high associated costs. Still, glass coatings could find use on such pieces due to their physical properties (durability, chemical inertia, tightness, etc.). Thermal spraying, using oxyacetylenic flame in particular, appears as a cost-effective solution permitting to circumvent the aforementioned disadvantages. This study aims at evaluating the quality of two types of coatings in terms of permeability. The first type considered coatings (resulting from a previous optimization of the spray operating parameters) sprayed directly on the substrates whereas the second one considered an additional brass underlayer manufactured by twin-wire electric arc spraying. The wettability of the glaze on the refractory substrate and on the brass underlayer was studied to comprehend the coating structural attributes (thickness, porosity, crazing, etc.) as well as their effects on the permeability. A specific measuring device was developed to assess permeability.

Suspension plasma spraying (SPS) is a fairly recent technology that is able to process sub-micrometric-sized feedstock particles and permits the deposition of layers thinner (from 5 to 50 µm) than those resulting from conventional atmospheric plasma spraying (APS). SPS consists in mechanically injecting within the plasma flow a liquid suspension of particles of average diameter varying between 0.02 and 1 µm. Upon penetration within the DC plasma jet, two phenomena occur sequentially: droplet fragmentation and evaporation. Particles are then processed by the plasma flow prior their impact, spreading and solidification upon the surface to be covered. Depending upon the selection of operating parameters, among which plasma power parameters (operating mode, enthalpy, spray distance, etc.), suspension properties (particle size distribution, powder mass percentage, viscosity, etc.), and substrate characteristics (topology, temperature, etc.), different coating architectures can be manufactured, from dense to porous layers. Nevertheless, the coupling between the parameters controlling the coating microstructure and properties are not yet fully identified. The aim of this study is to further understand the influence of parameters controlling the manufacturing mechanisms of SPS alumina coatings, in particular the spray patterns influence.

The purpose of this work is to optimise the chemical composition of perovskite coatings prepared by injecting a suspension of submicrometric LaMnO 3 perovskite particles (d 50 =~ 1 µm) in a direct current (d.c.) plasma jet. The perovskite powder composition, the particle size and the plasma parameters were modified in order to diminish the manganese evaporation. The process consists in mechanically injecting a well dispersed stable suspension of submicrometric perovskite particles in a dc plasma jet. In the process, large suspension droplets (~300 µm) are sheared into tiny ones (a few µm) by the plasma jet flow. Then the solvent is evaporated and the particles melt resulting in perovskite droplets of about 1 µm impacting on the substrate, the coating resulting from their layering. Such coatings are to be used as cathodes for the SOFCs (Solid Oxide Fuel Cells). Best results were obtained by injecting a stable suspension containing a 10 mol% MnO 2 doped perovskite powder with 3 µm particle size in an Ar plasma forming gas and 300 A of current intensity.

A perovskite suspension was air plasma sprayed (APS) with a direct current (dc) plasma jet. The process conditions including the standoff distance, plasma forming gases and their ratio influence on the perovskite deposits and splats characteristics were investigated. Particularly the molten state of particles, phases obtained, morphology and composition of splats were studied. The process consists in injecting a well dispersed stable suspension of submicrometric particles. The suspension was produced by attrition milling LaMnO 3 perovskite powder (mean particle size of 0.8 µm). The plasma forming gases influences drastically the obtained phases in deposits. When the plasma gas mixture contains hydrogen the heat transfer is too high and the perovskite phase is decomposed but when the plasma forming gases is Ar/He or only Ar, just a very little quantity of perovskite is found to be decomposed in the plasma jet. With Ar/He, perovskite splats are well melted, but with argon there is a high percentage of semi-melted and non-melted particles.

Plasma transferred arc (PTA) is now currently used for reclamation of worn materials or to provide wear or corrosion resistant coatings welded to the base material. Instead of injecting the powder in the molten pool created at the coated surface, another way to coat substrate surface before the PTA treatment has been studied. As the powder can not be simply deposited on the substrate surface because of the plasma flow which would blow it off before melting it, a tape casting process was used to obtain an adherent powder layer on the material surface. Its cohesion and adhesion to the substrate are due to the organic binder contained in the tape to form organic bridges between particles. In this paper, the electrical properties of NiCu (70/30) tapes deposited on cast iron substrates were first studied. It has been shown that the binder led to a low electrical conductivity of the layer. PTA treatment of the casted tapes has been carried out by starting the electrical arc on the metallic cast iron substrates. The process control by CCD camera allowed to observe that the NiCu particles fell in the melting pool created at the substrate surface. The study of the obtained alloy compositions has shown the drastic influence of the initial binder concentration in the tape. Moreover, before being treated by PTA, some NiCu tapes were heated in a furnace at 1100°C for 4 hours to remove the organic binder and sinter the layer. The coatings thus produced, which were characterized by a low electrical resistivity and a good adhesion to the substrate, were then treated by PTA. The surfacing alloy properties were compared to those obtained without heat treatment.

Plasma transferred arc (PTA) allows to weld a metallic coating to a metal substrate in order to improve their wear and corrosion resistance. This process is mainly used for steel reclamation and the principal applications are coatings of valves, valve seats in automotive industry and extruder screws for plastic industry. This paper describes the tape casting of NiCu and NiCoCrAlTaY particles on Ni-based alloys and the various organic additives used in addition to a homogeneous metallic film. The initial results of treating these films with PTA regeneration are described. Paper includes a German-language abstract.

Plasma transferred arc (PTA) is now currently used for reclamation of worn materials or to provide wear or corrosion resistant coatings welded to the base material. However, the powder injection in the molten pool created at the coated part surface is a critical parameter. In order to avoid coating reproducibility problems induced by the powder feed rate, the way to coat substrate surface with powder before the PTA treatment has been studied. As the powder cannot simply be deposited onto the substrate because of the plasma flow which would blow it off before melting it, tape casting process was used to obtain an adherent powder layer on the material surface. In this paper, tape casting of NiCu particles is described and the different organic additives used to obtain a homogeneous nickel copper film on cast iron and AG3 aluminum alloys are presented. The first results of the treatment of these films by PTA reclamation are then shown.