The replacement of cast iron sleeves through thermal spray coatings is an interesting alternative to improve the inter bore reliability, to reduce weight and to reduce the inter bore distance for automotive engines. Most of the actual production and pilot equipments use the ROTAPLASMA process to provide such functional coatings. However, the wire-arc spray process may often present different advantages like a higher deposition rate and a lower cost of the produced coatings. The LDS (Lichtbogendrahtspritzen) technology developed by DaimlerChrysler is a wire-arc process working with two wires whereas the PTWA (Plasma Transferred Wire Arc) process designed by Flame Spray Industries and the Ford Motor Company use a single wire. The present paper shows that the wire-arc technology may replace efficiently the APS (Atmospheric Plasma Spray) for the generation of thermally sprayed coatings applied on engine cylinder bores. A first rotating wire-arc spray system was previously designed and tested a few years ago. The present paper shows how computational fluid dynamic (CFD) may help in solving industrial problems: the FLUENT CFD code was used in order to perform improvements of the initial gun design.

A numerical model is presented for the computation of heat transfers during the APS thermal spray process. This model includes the contributions of both the impinging plasma jet and that of the particle flux on the substrate heating. The contribution of the impinging plasma jet is taken into account using a computational fluid dynamic model describing the impact of the plasma jet on the substrate. For this part of the work, a two-layer extension to the Chen-Kim k-s model was used allowing the description of both the turbulent plasma jet and that of the flow in the viscous sub-layer formed on the substrate surface. The contribution of the sprayed particles is taken into account considering their distribution in the spray jet. Since this is an important parameter that could affect the model accuracy, measurements of the deposit thickness profiles were first performed using the non-destructive acoustic microscopy method and the corresponding particle flux distribution was then deduced. Heat transfers inside the substrate were then computed using a three dimensional in-house code based on a finite volume approach. In the case studied, the results show that the contribution of the sprayed particles forming the coating is much more focalized than that of the plasma flow itself whereas the substrate nature has a strong influence on the thermal flux dissipation (not presented in the following). These elements are expected to provide useful information concerning the coating adhesion mechanisms and the formation of residual stresses during the coating elaboration.

In recent years, polymers have grown successfully in industrial applications such as protection against corrosion, chemical or wear resistance. However, the use of these materials is often limited because of their poor abrasion resistance. For example, PTFE is certainly a polymer that has the most attractive properties such as low coefficient of friction but it is characterized by a very low scratch resistance. These restrictions can be overcome by use of composite structure. This way, mechanical resistance can be then provided by ceramic materials. As a result, this study is devoted to feasibility of ceramic – fluoropolymer composite coatings by plasma spraying. Two types of organic powder (PTFE and PFA) and that of alumina powder were chosen. Blends of these compounds were then sprayed. Owing to thermal properties of both materials, specific spray parameters must be optimized. Two varied parameters were picked up (spraying distance and plasma gas mixture) and their effects on the coating quality were estimated by several types of characterization (morphology, polymer rate, roughness…).

A new family of spherical powders produced by the spray drying route has been developed. This paper describes as an example the manufacturing method of an Y2O3-coated aluminum powder. Atmospheric Plasma Spraying (APS) was used to test the corresponding coatings. Morphology and phases of powders and coatings were investigated by optical and scanning electron microscopy while the level of porosity was evaluated using image analysis. Results show that homogenous composite coatings can be obtained from cladded spray dried powders.