The number of parameters influencing the plasma spraying process is very high. Only a part of these parameters can be controlled online; some of them such as gas flows, current, voltage and spraying distance can be controlled easily, others such as particle temperature and velocity can only be controlled with substantially higher effort. As differences from parameter values preinstalled or given at the start of the process, the noise factors affect the coating properties in different ways and show big effects on the coating quality. Nevertheless there is only little knowledge about the significance of several noise factors and about the influence of small process parameter fluctuations on the coating properties. Because some of these noise factors such as plasma torch degradation cannot be avoided, the aim of this work is to determine the sets of coating parameters, where the influence of noise factors is minimized. This should be achieved by using online diagnostic tools, that afford the observation of fast and easy controllable process characteristics. On the other hand process errors shall be identified in an early process stage using appropriate diagnostic methods.

The aim of this study is to propose coatings that could potentially replace hard chromium as a means of corrosion and wear protection. Two NiCrBSi coatings are evaluated, one produced by laser cladding, the other by atmospheric plasma spraying with a post-laser treatment. Although laser-clad NiCrBSi exhibits the best technical properties, the APS coatings were found to be more environmentally justifiable based on the use of life cycle assessment (LCA) software.

An optimized powder/suspension based atmospheric Plasma Spray (PS) process, using a Triplex Pro 210 TM torch, was implemented to elaborate Cu:TiO2 surface coatings on stainless steel. Nanometric Degussa P25 TM powder was prepared in a water-based suspension and co-sprayed with a Cu spheroidal powder. The bacterial reduction, evaluated with 1h-exposure to Escherichia Coli (E. Coli), was two times higher for the Cu:TiO2 coating compared to the bare stainless steel substrate. Since the coatings obtained by plasma spray are relatively porous, their antibacterial efficacy was compared to smooth Ag and Cu doped titanium nitride (TiN) films obtained by physical vapor deposition technique (PVD). For the same exposure time, the PVD smooth coatings showed a much lower antibacterial efficacy proving the topography effect on bacterial adhesion.

Surface treatments and coatings are widely used to protect components from wear and corrosion. Of all available methods, thermal spraying is arguably the most versatile with regard to coating material and morphology. Surface roughness and porosity can be adjusted in a wide range depending on the requirements. However, as-sprayed coating surfaces inevitably exhibit a certain roughness necessitating post-treatment if a smooth surface is required. The surface roughness of thermal spray coatings is usually determined by the used powder fraction and the particles’ melting degree. Using wires as feedstock material allows for a certain influence on the particle size distribution by adjusting process parameters. In this study, the influence of nozzle geometry and atomizing gas pressure on coating quality, surface roughness and cost-efficient post-treatments of wire-arc sprayed Fe-based alloys with a wide hardness-range is investigated. To allow for easy transfer to real components, the sample geometry is based on real world examples of coatings for new components and repair of worn parts. Using adapted process parameters and air-flow, the surface roughness could be decreased to allow for a less time-consuming post-treatment by grinding. Especially in repair coatings for large area applications requiring a smooth surface finish, significant runtime and cost reductions are feasible.

Excimer laser annealing provides a rapid and efficient means for surface alloying and modification of ceramic materials. In this study, Alumina-13% Titania coatings were sprayed with a water-stabilized plasma spray gun. The coated surface was treated by Excimer laser having a wavelength of 248 nm and pulse duration of 24 ns. The surface structure of the treated coating was examined by field emission scanning electron microscope and X-ray diffraction (XRD). A detailed analysis of the effects of various laser parameters including laser energy density (fluence), pulse repetition rate (PRR), and number of pulses on the morphology and the microstructure of the coatings are presented.

This study aims at evaluating the erosion resistance at temperature of several hard coatings, including: CrC-NiCr by HVOF, Fe-based alloy by Arc Spray, NiCrBSiFe by powder flame spraying. These coatings are to be used for the recovery of highly eroded walls (above 10 mm thickness) of gray cast iron in the exhaust ducts in heavy-fuel engines. The erosion test consists of erosive particles thrown through a high temperature gas jet, for 5 cycles of 5 minutes, according to ASTM G211-14 (modified). Coated samples are subjected to a fuel gas-torch reaching a front temperature of 450ºC and a back temperature of 90ºC (water cooled), simulating the actual application. The eroded samples are characterized using EDS, and SEM. The results show the erosion rate of each material/system, and their corresponding erosion mechanisms. Thus, the results allows for the selection of an optimum coating for this surface recovery application.

Additive manufacturing (AM) techniques give access to completely new manufacturing processes. AM techniques using metals, ceramics, or plastics feedstock are predestined for lightweight construction and for components with complex shapes or internal functions. AM processing with plastics stands out due to the low density of polymers, a good process capability, and low initial costs. The properties of polymer components are extremely dependent on the utilized plastics and the reinforcements, e.g. in the form of fibres. Furthermore, coatings can improve the properties and enhance the possible range of applications for plastics. In the present study, PLA (polylactic acid) was printed utilizing Fused Layer Modeling (FLM). The surfaces of the PLA samples were directly structured with pits with different widths during printing. Subsequently, the surfaces were coated with ZnAl 2 by means of Twin Wire Arc Spraying (TWAS). Adhesion tests meeting DIN EN 582 were conducted to measure the adhesion of the coating on the structured plastic surface. The results were compared to the adhesion of ZnAl 2 coatings on grit blasted and as-built surfaces. Overall, the surface adhesion was significantly better for the samples with directly structured surfaces. Hence, a direct structuring of the surface during a 3D building process promises to be an outstanding possibility to prepare surfaces prior to coating processes.

In this work, pure silicon and Ni-P coated silicon powders were cold sprayed on copper foil. To thicken coating layers, 2-pass and 3-pass coatings were carried out. In the case of Ni-P coated silicon powders, coated anodes show excellent charge-discharge characteristics after two passes. For the pure silicon powders, however, even if a 2-pass operation is performed, the additional attached silicon mass is only 2~3 %. This means that multi-pass spraying is not an effective way to increase the thickness of pure silicon coatings produced by cold spraying.

The enhancement of the surface characteristics and corrosion resistance of cobalt alloys is under continuous examination for its biomedical applications. In this work, the investigation of corrosion performance of cobalt alloy coated with HA and HA/ZnO reinforced powders using plasma spray technique revealed that on the continuous increase of ZnO reinforcement the corrosion resistance improved progressively. The increment in surface hardness and drop in surface roughness was examined with the rise in ZnO content. Each coated sample exhibits a hydrophilic property. According to SEM and EDX investigations, homogeneous distribution of HA/ZnO coatings and intact reinforcement of ZnO in pure HA powder was noticed. All of the coated specimens maintain their morphological integrity, ensuring excellent protection of the prepared samples. The obtained outcomes denote HA/ZnO reinforced coatings on CoCr alloy as a suitable combination of enhanced surface properties and excellent corrosion resistance for future bone implant practices.

Thermal sprayed coatings are frequently used in corrosive environments, even when their major purpose is to provide wear or thermal resistance, rather than corrosion resistance. This includes Thermal Barrier Coatings (TBC), where high porosity is a desired feature to give good thermal protection. However, as this proves to be a limiting factor in the corrosion protection, a trade off is involved. This is because the interconnected porosity in TBCs allows the corrosive media to reach the coating-substrate interface, which eventually leads to delamination of the coatings. This work addresses the problem of permeability of TBCs which can lead to premature delamination due to interfacial corrosion. The coatings studied were yttria-stabilized zirconia TBCs. A simple infiltration technique has been proposed using sol-gel ceramic precursors. The precursors studied include aluminum isopropoxide or pre-hydrolyzed ethyl silicate, which decomposed to alumina and silica respectively, at surface heat treatment temperatures as low as 550°C. In addition to sealing the surface, it is believed that some level of compressive stress is generated on the surface of TBCs on cooling from the processing temperature. Electrochemical tests in 3.0% NaCl have been carried out to study the effectiveness of the sealant. These potentiodynamic tests as well as permeability tests show a considerable decrease in interconnected porosity with sol-gel modifications of the coatings.

Cold spraying consists in depositing a variety of metals as dense coatings onto metal surfaces. Indeed, copper, stainless steel, nickel, chromium, aluminum, cobalt, titanium, niobium and other metals can all be deposited, as well as metal alloys according to these base-metals and braze powders. The particle-substrate contact time, contact temperature and contact area upon impact are parameters influencing physico-chemical and mechanical bonds. The resultant bonding arose from plastic deformation and temperature at the interface which illustrates why metal coating cannot be sprayed onto rough ceramic substrates. Laser surface texturing has been used as prior treatment to create specific topography. Metal-ceramic has demonstrated a non-deformation of the substrate minimizing intimate bonds. Particle compressive states indicate anchoring mechanisms for laser textured surfaces. Consequently, cold spraying parameters depend on the target material and a methodology can be established with particle parameters (diameters, velocities, temperatures) and particle/substrate properties to adapt the surface topography. Mechanical adhesion is a key issue in cold spray process. As a result, laser surface texturing is a promising tool to adapt the surface to improve adhesion. Metallization process can be achieved.

Thermal barrier coatings typically consist of a ceramic topcoat and a metallic bond coat that promotes adhesion and protects the substrate from corrosion. This study evaluates surface preparation processes used prior to the application of the bond coat layer. In the experiments, NiCrAlY bond coats are plasma sprayed onto Inconel substrates prepared by various methods, including dry and wet blasting and solid CO 2 cryogenic cleaning. At different points in the process, samples are extracted and characterized based on surface roughness, subsurface hardness, morphology, adhesion, interface contamination, and coating thickness and structure. Paper includes a German-language abstract.