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.

PTA (Plasma Transferred Arc) reclamation of aluminum alloys by hard materials with a much higher melting temperature is very difficult. This is due to the high thermal diffusivity of these al1oys. Below a critical heat flux φc nothing happens and over φc the substrate melts very rapidly contrarily to what is observed with steel substrates. That explains probably why PTA is mainly used for steel reclamation. Thus the knowledge of heat flux transferred to the anode is a critical point to develop PTA reclamation on aluminum alloys and this is the aim of this paper. An experimental set-up was built to study the heat transferred to three substrates made of different materials : cast iron for reference, aluminum alloy and copper for its high thermal conductivity. The plasma torch was a Castolin Eutectic gun and allowed to inject a sheath gas around the plasma column. The copper, aluminum alloy and cast iron substrates, easily interchangeable, were the top of a water-cooled calorimeter allowing to determine the variation of the received heat flux with the working parameters : arc current, stand off distance, plasma forming gas momentum, sheath gas composition and momentum. The determination of the arc electric field allowed to calculate the arc diameter which was compared first with pictures taken with a video camera and second, with wear traces left on the anode material. Several correlations have been established to characterize the arc voltage and the anode heat flux.

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.