In light weight constructions, research focuses more and more on ecological aspects of materials. In this way vulcanized fiber relive a renaissance because it is produced from renewable raw materials. Vulcanized fiber is a composite material, which was approximately discovered in 1855. It is manufactured by parchmentizing of pulp with the use of a zinc chloride solution. This material is well known for its good strength to weight relationship, but it is susceptible to the contact with aqueous fluids and also shows only a low resistance to wear. Therefore, a functionalization of the surface is needed. The functionalization can be realized by thermal spray processes to increase the potential of vulcanized fiber. Especially the pretreatment of the specimen to enable the coating application is one of the key topics of this paper. Vulcanized fiber is a thermal sensitive material. The impact of hot spray materials can cause undesired reactions such as the combustion of fibers on the substrate’s surface. To reduce this effect, twin wire arc spraying and low pressure cold gas spraying processes were used to apply low-melting materials (copper, zinc) onto the specimen. Thereby, the influence of the coating on the vulcanized fiber surface was investigated. In addition, non-destructive testing methods were evaluated to gain information about the vulcanized fiber.

Well known that high temperature corrosion resistance of thermal barrier coatings (TBC) may depend not only on chemical composition, thickness, the rate of formation of TGO layer, but also on the presence of post treatment. In this work we studied the influence of presence of post treatment on properties of TBC particularly on high temperature corrosion. TBC system were sprayed on Ni-based substrate and consists of HVOF NiCo-based bond coat (BC) and APS yttria-stabilized zirconia (YSZ) top coat. Thermal cycling test in the presence of corrosive environment was used to determine effect of post treatment presence. Before and after Thermal cycling test cross-section of specimens were studied by SEM and EDX analyzes. Preliminary results demonstrated that high temperature corrosion resistance of TBC with APS-top layer and HVOF-bond layer can be improved by applying post treatment.

This study investigates the effects of laser remelting on plasma sprayed YSZ thermal barrier coatings using a pulsed laser with and without induction preheating. It is shown that induction preheating decreases the laser threshold energy required for full remelting, which effectively reduces crack density. Induction preheating also helps in developing a steadier melt temperature and in decreasing thermal gradients between successive remelting passes. XRD analysis shows that it can reduce the amount of monoclinic phase as well.

This study reports on the effect of combined pulsed laser ablation and laser pre-heating surface pre-treatments to cold spraying Ti and Ti-6Al-4V on coatings’ microstructure, bond strength and cohesive strength. The Ti and Ti-6Al- 4V coatings were sprayed on pure titanium and Ti-6Al-4V substrates, respectively. Coatings were characterized by SEM and porosity level was evaluated through image analysis. Bond strength was evaluated by standard ASTM C633 pull tests and by the laser shock (LASAT) technique. Cohesive strength was evaluated by the cross-section scratch test method. Results show that among the spray conditions used in this study, laser pre-treatment yielded high bond strength (such that all cases had higher cohesive strength than the epoxy glue). The LASAT technique provided a means to evaluate the influence of the laser ablation energy density and the laser pre-heating temperature. For both Ti and Ti-6Al-4V coatings, surface pre-heating increased the coating bond strength to the substrate. The laser ablation process would either increase or decrease the bond strength of the coating to the substrate depending on the laser energy density. The laser energy density needs to be adjusted as a function of the surface pre-heating temperature in order to optimize bond strength improvement. Coating cohesion did not improve with continuous laser pre-treatment in-between passes. However, the laser pre-heating helped reduce the coating porosity.

Dry-ice blasting, as an environmental-friendly method, was used during atmospheric plasma spraying for improving coating properties. This process is believed to be capable to reduce the porosity and the oxide of the coating and to increase the deposition efficiency, etc. Considering dry-ice pellets are carried and accelerated by compressed air through a convergent-divergent nozzle, the computational fluid dynamic (CFD) approach was firstly employed in this study to evaluate the effects of nozzle geometry, accelerating gas conditions as well as properties of pellets, on the pellet velocity variation and further to optimize the process. Moreover, the experiment with a steel powder was then carried out and the results indicate that a denser coating with a lower content of oxide can be achieved with the application of dry-ice blasting during the plasma spraying.

Solid-particle erosion of metals and alloys at elevated temperatures is one of the main reasons of the damage of components used in the energy production and utilization industries. Application of protective coating systems can be an attractive and economically reasonable solution for preventing the failure and increasing the durability of the components working in severe conditions of high-temperature corrosion and erosion. However, thermal spraying of intermetallic materials that have excellent high-temperature corrosion resistance is limited because of their low ductility. Present work reports the results of the investigation of abrasion wear resistance at elevated temperatures of combined coatings, which include the intermetallic layer. Such iron aluminide layers have been formed as a result of diffusion during the heat post-treatment of arc-prayed metallic coatings combining Fe- and Al-based layers. Post-treatment of arc-sprayed coatings was carried out by means of infrared radiation and induction heating. It was shown that the abrasion resistance of the developed coating tested at elevated temperatures (T > 500 °C) is considerably higher than that of low-alloyed steel and some nickel-based alloys and depends on the test load condition. The high performance of intermetallic-based graded coatings at elevated temperatures makes them interesting for applications as a low-cost erosion-corrosion-resistant material.

Cold spraying is particularly suitable for elaborating heat and oxidation sensitive coatings. Due to the fact that the particles are not melted during the spraying process, it is thus possible to elaborate coatings without chemical modifications. Nevertheless, according to the materials considered, some interface defects can be detected inducing an inadequate adhesion between the substrate and the coating. Bonding mechanisms are not only strongly dependent on the particle velocity but also on the state of the surfaces. By this way, surface pre-treatments can be necessary to improve adhesion. From all the surface modification technologies, laser ablation process is very interesting due to its flexibility by using optical fibers and due to the perfect control over the treated area. It is then possible to interact with the material during all the spraying process on the substrate surface as well as on the interface layers. This is particularly the aim of this study which consists in exploring the laser influence, implementing the PROTAL process, on the different interfaces quality for coatings elaborated by cold spray on metallic substrates. By controlling the chemical composition of the materials, the coating cohesion as well as the adhesion level, coatings were sprayed on pure titanium and titanium and nickel based alloy substrates.

Surface treatments are often necessary in thermal spraying to modify the surface properties of materials and then to improve the coating adherence. Several techniques exist. Among them, conventional techniques such as sandblasting, chemical degreasing and some others like high pressure water jet or laser ablation can be implemented. However, whatever the results, some drawbacks can always be listed according to the materials considered (sensitive materials, low adherence level). By this way, new techniques have to be developed. Considering the laser technology, some new treatments can be particularly suitable for surface modifications. Based on the printing technology, laser texturing implementing fiber laser technique combined with a scanner permits to engrave quickly uniform holes on the surface. Applied as a surface treatment before spraying step, the potential of such technique is particularly observed in this study. According to the laser parameters, several points can be analysed such as size (diameter and depth) and the distance between each holes. After surface characterizations by SEM observations and roughness measurements, adhesion tests were then implemented. Considering NiAl coatings sprayed on textured aluminium alloy substrates, some very interesting adherence results (55 MPa) were measured in comparison to the conventional treatments (45 MPa after degreasing and sandblasting) as well as laser ablation technique (34 MPa).

For production of intermetallic coatings, various types of Ni-Al powders were plasma sprayed at different spray distance and the effect of heat treatment on phases, microstructures and microhardness of coatings was examined. XRD, SEM, EDAX and microhardness were used for characterization of the coatings. Heat treatment of the coatings in various temperatures caused changes in hardness of the coating, increased percentage of intermetallic compounds, completed intermetallic production reactions, but did not change porosity percent. Increasing heat treatment temperature caused oxidation and decreased improvement of coating properties.

The plasma surface hardening, as one of methods of surface treatment by heating sources with high power density, finds presently wide and effective application in conditions of short-series and single-part (including repair), and large-scale and wholesale manufacture. One of effective methods for research and optimization of the plasma surface hardening is the use of computer simulation. The complex mathematical model of steel parts hardening at high-speed plasma heating is presented in the article. Model includes mathematical description of steel parts heating and cooling, and also forming of their stress-strain state. The distinctive feature of the presented model is taking into account under modeling of phase transformations and plastic deformations. It allows to achieve the maximally adaptation of the simulation results to real physical characteristics of the process. The algorithm of model computer realization, based on the application of final elements method is offered.

To avoid the constraints due to the conventional surface preparation before thermal spraying (degreasing and sand-blasting), the PROTAL process was developed implementing a Q-Switched Nd:YAG laser with a very short pulse duration to prepare the surface simultaneously to the coating buildup. Until now interesting results were obtained both from the adhesion and economical points of view. Specific parameters were developed according to the spraying process (APS, HVOF, wire arc), the powder (Cu alloy, Al 2 O 3 , WC-Co, ...) as well as the part nature (Ni alloy, Magnesium, steel, aluminium alloys, etc.). Considering the wide development of thermal spray applications in the automotive industry, new developments of the PROTAL process were considered in order to reach the feasibility of an internal laser treatment of the parts. After a presentation of the implementation of a new laser head in the thermal spray environment, some results concerning the case of a metallic coating (ferrous alloy) on a metallic part (aluminium alloy) will be presented.

It has been confirmed in the flattening behavior of the thermal sprayed particles that the splat shape on the flat substrate surface changes to a disk type from a splash type at relatively narrow temperature range with increasing the substrate temperature. The temperature increasing actually causes a certain non-reversible change on the substrate surface, because the changing effect is maintained till the substrate is cooled down to the room temperature. We have pointed out that this non-reversible change on substrate surface due to the heating might be the possible domination for the transition phenomenon of the thermal sprayed particles, that is, the essence of the substrate surface change due to the heating is surface roughness in nano-meter range. In this study, several kinds of substrates once heated to some elevated temperature were analyzed precisely by atomic force microscope (AFM) to characterize the change in their surface roughness character. The fundamental static wetting behavior of the substrate surface by a water droplet was investigated for the reference in the present study. The results obtained revealed that the change of the substrate surface topography in nano-meter range affect most effectively the wetting behavior of the droplet or splat on the surface. Hence, the substrate heating may bring about the change in the physical way on the substrate surface and this change induces the transition phenomenon.

As already shown 3 years ago, the preoxidation of smooth (Ra < 0.05 µm) low carbon steel substrates in a furnace under a CO 2 rich atmosphere at atmospheric pressure allows the formation of a wustite (Fe1-xO) layer which improves significantly the adhesion (> 55 MPa) of alumina coatings in spite of the rather low roughness (0.10 µm < Ra < 1.00 µm) of the oxidized surface. This contribution is devoted to a more precise study of the wustite layer and its interface with the alumina layer by X-ray diffraction (XRD), Mossbauer spectroscopy and scanning electron microscopy (SEM). Firstly the substrate was oxidized under different temperatures and durations in order to control the oxide layer thickness and structure. Secondly the substrate samples were preoxidized during 15 minutes at 1273 K under CO 2 atmosphere and, afterwards, preheated by the plasma jet in air just before coating. In this case the analysis was focused both on the alumina splat formation and the interface between splat and the oxide layer. Only a non-continuous alumina layer (a few splats) was sprayed: this allowed surface analysis down to the substrate through the alumina layer and the interface. This method avoids any modification of the searched information by a complex specimen preparation as required in the case of transmission electron microscopy (TEM) for example. For the steel surface preheated in CO 2 atmosphere, before spraying, SEM observations and XRD patterns showed the presence of a continuous oxide layer formed by wüstite crystals with an average size of 1-5 µm. After deposition, splats consisted of transitional alumina (γ phase) but the underlayer was no longer pure wüstite. XRD and Mossbauer identified magnetite at the surface of the oxide scale in contact with alumina. This can probably be considered as the result of a partial topotactic transformation of wustite into magnetite, since no morphological change of the oxide layer has been observed. It has been established that this transformation is a consequence of the pre-heating treatment, and not due to any reaction with alumina. It is worth noting that, under these conditions, γ alumina has a spinel structure analogous to that of the magnetite phase with which it was in contact: the alumina structure was possibly induced by that of the magnetite underlayer.

Generally, the surface of a substrate is roughened by blasting in pretreatment thermal spraying. Since some of the grit remains on the substrate surface, sprayed coating and the adhesion property characteristics are degraded. However, it seems that there is almost no research on this problem. In this study, residual grit is quantitatively evaluated, and a technique for reducing grit is proposed. For residual grit reduction, a solid lubricant was used, and applied to the surface of a substrate or grit; reduction of residual grit was confirmed. After blasting with solid lubricant, it remained on the substrate surface, which could be removed by heating the substrate.

The PROTAL process combines a laser surface preparation and the thermal spraying stage. This laser surface preparation avoids some of the traditional drawbacks of the degreasing and sand-blasting stages which is an important factor especially for the notch-sensitive materials. Previous studies showed that deposit adhesion obtained with the PROTAL process is similar to that produced by traditional surface preparation despite the absence mechanical anchorage offered by surface roughness. In order to get a better knowledge of the effects of such a laser treatment, a Ni-5%Al coating was plasma sprayed using the PROTAL process under different surface conditions. The morphology of the impinging splats and adhesion of the deposits were then examined. Removal of the surface contaminants, adsorbates and oxides is confirmed and the role of the laser irradiation on the coating adhesion is discussed.

This paper investigates the adhesion of thermally sprayed ceramic particles on metal substrates. Two aluminum oxide powders are applied to nickel-oxide coated steel substrates by detonation and vacuum plasma spraying. SEM and XRD fracture analysis is used to examine the ceramic-metal interface and the morphology of fracture surfaces. In all test samples, failure occurs in the alumina, not at the interlayer boundary, indicating a high level of adhesion between the ceramic and nickel oxide layers. Paper includes a German-language abstract.

This paper investigates the effect of laser treatment on alumina-TiO 2 coatings deposited by detonation spraying. It describes the changes observed in the microstructure and hardness of the remelted layers. The originally lamellar structure is transformed into a fine, pore-free columnar structure in which the grains are oriented perpendicular to the interface between the layer and substrate. The remelted zones contain alpha-aluminum oxide as the main phase and are characterized by high microhardness, although a few defects were observed on the periphery. Paper includes a German-language abstract.

This paper examines the influence of spark plasma sintering (SPS) on plasma-sprayed hydroxyapatite (HA) coatings. For comparison purposes, a conventional heat treatment is also carried out. The surface microstructure as well as the crystallinity of each layer is determined by means of SEM and XRD analysis. Test results show that the crystallinity of the layers increases with increasing SPS temperature up to 800 °C and a large amount of β tricalcium phosphate is formed. Paper includes a German-language abstract.