In state-of-the-art manufacturing of sliding bearings, brass components are soldered to respective parts, which is costly and energy-intensive. Furthermore, up to now most bearings still contain lead, which by EU regulations for new part has to be omitted due to associated health risks. Cold spraying can be employed as additive manufacturing technique and opens the perspective to deposit the requested bearings in desired leadfree layout where needed. Aside cohesion and tribological behaviour, sufficient adhesion of the coating is essential for applications. The present study aims to systematically elucidate the influence of surface roughness on adhesion. The surface roughness was adjusted by varying the grit blasting material, grit size, blast pressure, blast distance and substrate material with the aim to study influences by impact conditions, surface topography on particle deformation and bonding in cold spraying. The results show that the adhesion strength reaches a maximum for a certain roughness. The ideal surface roughness to ensure good adhesion of cold-sprayed coatings apparently depends on specific impact conditions related to the powder material strength but also on the substrate material strength and particle size distribution. By systematic tuning of blasting conditions, coating adhesion can be increased by about a factor of two, thus meeting the requirements for new lead-free bearings.

This research demonstrates the use of cold spray (CS) as an additive manufacturing process to manufacture reflective aluminium coatings. Nitrogen was used as a carrier gas at various gas heating temperatures. Following deposition, the coatings were finished using a number of machining and/or polishing processes to surface roughness values of 20-150 nm. The samples were characterised with respect to total reflectivity within the wavelength range of 400-1800 nm, porosity, surface roughness, and density. The reflectivity of the coatings approached that of bulk material, and 99% dense coatings were obtained. Increasing the gas heating temperature did not decrease the porosity with the lowest gas heating temperature found to deliver the best reflectivity. This work demonstrates that CS can be used to coat thin layers of aluminium onto various materials, which can be subsequently polished to create composite reflectors. This provides a novel reflector with the reflectivity of aluminium, and the structural and thermal properties of the substrate material, allowing for greater flexibility in the manufacture of reflectors.

Additive manufacturing (AM) has already been evolved into a promising manufacturing technique. In order to achieve the performance of conventionally manufactured components, additively manufactured components must meet at least the same mechanical and physical requirements. Due to the layer-wise building process, the properties of additively manufactured components differ from that of bulk materials. Within the scope of this study, selective laser melting (SLM) was employed to manufacture specimens which serve as substrates for a subsequent coating process. An Inconel 718 (IN718) alloy served as AM feedstock. Mechanical posttreatments were applied to the AM samples and rated with respect to the successive thermal spraying process. The produced AM samples were examined in their initial state as well as under post-treated conditions. In this report, the resulting surface roughness was analyzed. Different AM samples were coated by means of high velocity oxy-fuel (HVOF) spraying and atmospheric plasma spraying (APS). The interface between the thermally sprayed coating and the AM substrate was metallographically investigated. Adhesion tests were conducted to scrutinize the bond strength of the coating to the AM substrate.

For fabrication of high strength carbon nanotube (CNT) reinforced Al matrix composites, the uniform dispersion, strong interface bonding and high structural integrity of CNTs have been regard as the three most important issues. In this work, two distinct approaches, namely high shear dispersion (HSD) and shift-speed ball milling (SSBM), were applied to disperse CNTs (1.5 wt.%) into pure Al powders. These two kinds of CNTs/Al composite powders as well as pure Al powders (as comparison) were deposited onto stainless steel plates under the same processing parameters. The deposition efficiency, microstructure, as well as the structural integrity of CNTs in the coatings produced from different starting powders were comparatively investigated. According to the XRD and Raman analysis, the brittle Al 4 C 3 phase was not formed in both CNTs/Al composite coatings. Some structural damages of CNTs were found in both composite coatings, especially the one fabricated from HSD composite powder. The dispersion of CNTs onto Al particle surfaces by HSD approach did not achieve significant strengthening effect on the composite coatings, but adversely affect the metallic bonding of the particles. The microhardness of CNTs/Al composite coating produced from SSBM powders reached to ~115 HV0.1, showing a significant improvement compared to the pure Al coating. The strengthening mechanisms of the cold sprayed CNTs/Al composite coatings were also investigated.

Additive manufacturing offers the ability to produce complex parts or shapes by layer based printing method using 3D modeling software equipment. Among the different technologies, 3D Printing and Rapid Prototyping are well established. However, thermal spraying makes a contribution towards this field as Cold Spray for repairing metal components. VLPPS and PS-PVD are both thermal spray processes using plasma technology in a very low-pressure controlled atmosphere. These conditions allow to obtain different precursor states: molten and/or vapor. As a result, the microstructure of the coating is unique in the community (lower scale elements, pore architecture) and the properties are improved. Furthermore, vapor phase of metal can react with some gases to generate oxides or nitrides. Another opportunity presented in this study is the ability of this vapor phase to fill mold. The objective is to demonstrate that VLPPS process can be employed as an additive manufacturing device to create well-defined objects.

This paper reports on the performance evaluation of stainless steel (SS) thermal spray coatings aimed at shielding lightweight aluminum (Al) brake rotor disks from excessive heat and providing an adequate tribological surface in contact with brake pads. Coating wear, corrosion and heat resistance performances were evaluated using pin-on-disk, cyclic corrosion tests and thermal cycling using a custom laser rig, respectively. Arc spray optimized coatings displayed lower or equivalent wear rates when compared with the baseline gray cast iron disks, with similar frictional behavior. However, arc spray coating exhibited low adhesion which limits the maximum coating thicknesses achievable and leads to early coating spalling after about 1000 thermal cycles. Arc sprayed coatings also corroded and delaminated under corrosion tests. Optimized cold spray coatings present high corrosion resistance and could resist above 10,000 thermal cycles without spalling. However, cold spray coatings exhibit wear rates at least 4 times those of the cast iron. Taking advantage of both types of coatings, it was found that the production of a duplex coating made of a cold spray bond coat and an arc spray top coat could meet the requirements for protecting Al disks, with near 50% weight reduction.

Natural gas represents the lowest cost, most widely available fuel gas for high velocity oxygen fueled (HVOF) thermal spray. Natural gas is a mixture of hydrocarbons and other gases that may fluctuate over time or from one location to another based on the source of the gas and the processing it has undergone before delivery to the end user. The present work seeks to determine the impact that changes in natural gas composition can have on the HVOF process in order to ensure that quality and consistency of the resulting coatings is not negatively impacted. Gas chromatograph data was collected daily from a natural gas supplier in Europe and the Wobbe Index was used to compare the energy content of each reading. Customized blends were used for laboratory spray trials to explore the potential impact that these changes might have on the HVOF process and the resulting coatings. Presently, there is some evidence of coating degradation due to shifts in natural gas composition when all other process parameters are held constant. These observations are the subject of ongoing development work.

In times of duality of combustion engine and electric motor propulsion the automotive industry is developing both powertrain systems. Weight reduction and enhancement of efficiency plays a vital role in the conception of combustion engine for passenger cars. The thermal spray technology therefore is trend-setting as it achieves both aims. GROB-WERKE have, as reported previously, developed and integrated their GTS (GROB Thermal Spray) process for steel deposits in aluminum cylinder bores into their production lines. Further effort was now made to improve performance and versatility. The application of measurement and simulation technics hand in hand with extensive experimental investigation in spray deposit diagnostics as well as plasma and particle jet analysis led to highly developed and advanced deposit microstructure and cylinder bore topographies. Complex and extensive CFD (Computational Fluid Dynamics) simulation of the gas and particle flow gave the thermal spray process the highest performance, efficiency and product cleanliness.

The restoration of a valuable historic vehicle is a complex operation; indeed, the vehicle value is directly connected to the degree of authenticity of the restoration. Corrosion has been observed to reduce the thickness of metal sheets from the original 0.03 in. (0.8 mm) to only 0.015 in. (0.4 mm) or even less. In such cases, traditional restoration methods could lead to further deterioration of the metal body. In this article, the authors describe an innovative thermal spray method for restoring metal sheets to their original thickness. This method permits restoration of the original body, preserving the degree of authenticity of the vehicle. The method has been patented by Ferrari SpA.

Binary spinel-type metal oxides (AB 2 O 4 ) semiconductors, including ferrites (AFe 2 O 4 ), are attractive photocatalysts thanks to their excellent visible light response and good photochemical activity and stability for the photodegradation of organic pollutants. Currently, their synthesis proceeds via conventional chemical routes that follow rather tedious protocols and the final preparations consist in nano-powders, a form that is not exempt of EHS (Environment, health and safety) risks along their handling. From an industry perspective, it is desirable to dispose of an efficient and preferably simple synthesis route capable to produce photocatalytic preparations in a non-dispersible form, for instance in the form of robust films attached on solid substrates. We report herein a single-step method based on the Solution Precursor Plasma Spray (SPPS) process that enables the preparation of promisingly active ferrite-based photocatalytic films, namely CuFe 2 O 4 and ZnFe 2 O 4 . We have investigated various types of precursor solutions, including the atomic A/Fe ratios, solvent type and solute concentration, and studied the evolution of the phase composition of the resultant CuFe 2 O 4 and ZnFe 2 O 4 films by XRD. The corresponding surface morphologies and energy bandgaps were also studied by SEM and UV-Vis spectroscopy, respectively. Then the photocatalytic activities of the selective ferrite films were evaluated through the degradation of aqueous solutions of the Orange II dye under different light irradiations. The results of the overall work also revealed that SPPS process represents a fast, one-step, versatile alternative compared to conventional multi-step processes, which is suitable for preparing complex composition metal oxide film-formed photocatalyst.

A multi-layered thermal-sprayed coating system, developed as a resistive heating system, was deposited on a carbon steel pipe. The feasibility of using a 50Cr-50Ni coating as a heating element on top of a conductive substrate was studied. Alumina was deposited to serve as an electrically insulating layer between the metal coating and the substrate to restrict the flow of electrons from the metal alloy heating element to the steel substrate. Continuity, homogeneity, and adhesion of the coating were qualitatively analyzed by studying scanning electron microscope images. The performance of the heating system was determined by measuring the ice temperature and the times required to heat and melt the solid ice that was formed within the pipe. It was found that the coating system was able to generate the heat required to melt the ice in the pipe, thus avoiding the detrimental effects on the pipe of internal liquid freezing. This suggests that the proposed novel resistive heating system can be used on an industrial scale to mitigate or avoid the detrimental effects of ice accumulation in steel and other metallic pipes.

Magnesium light weight alloys are currently being studied as implants due to their biodegradability. However, its applications are limited by high rate hydrogen evolution during corrosion. Coating on this substrate is one of the ways to reduce the rate of corrosion and increase the life of this type of implant. Hence, hydroxyapatite (HA) was coated on the substrates by using high velocity oxy- fuel (HVOF) spraying. The main purpose of such coatings is increasing bioactivity as well as corrosion resistance of the Mg alloy. Crystal structure was characterized by X-ray diffraction (XRD). Crystallinity of the coating was about 70% in which HA is dominant phase. The amounts of hydrogen gas released during magnesium corrosion tests in simulated body fluid (SBF) were measured to evaluate the corrosion resistance of the coated samples. This coating could decrease hydrogen evolution from 100 per cm 2 .mL to about 15 per cm 2 .mL after 29h of immersion time.

The degradation of pump components by corrosion and complex damage mechanisms, e.g. erosion and cavitation leads to high costs through replacement and maintenance of parts. To increase the lifetime of cost-efficient components with superior casting properties, gray cast iron parts are surfaced with duplex stainless steel using an inert shielding gas metal arc welding process. The dilution of the surfacing increases with both increasing heat input and increasing thermal conductivity of the shielding gas. The microstructure is highly affected by the cooling conditions that may enhance diffusion processes and eventually lead to precipitation of deleterious carbides. Higher heat input and prolonged cooling duration during surfacing lead to high dilution and a pronounced carbide network and thus, substantially reduced corrosion resistance in artificial seawater. The corrosion of the surfacings in the potentiodynamic polarization test is driven by selective corrosion of the phase boundary between carbides and chromium-depleted austenite. Passive behavior is observed for coatings with low dilution and higher cooling rates, which showed homogeneous chromium distribution and no interconnected carbide networks. In conclusion, the corrosion behavior of gray cast iron was improved by surfacing with duplex stainless steel.

Ni-Co-Al-Li oxide (NCAL) is an important catalyst material for low-temperature solid oxide fuel cells (LTSOFCs). In this paper, air-plasma spray (APS) coating technology was applied to make NCAL layers on porous steel supports for the LTSOFC. The results showed that NCAL was well deposited on the skeletons of the support. Due to the plasma heating, the original LiMO 2 phase transferred to Li-deficient Li 0.4 M 1.6 O 2 phase simultaneously forming Li-rich oxide. New fuel cell structures were designed. The stability of the fuel cells was evaluated by performing galvanostatic test at 500 °C. The influence of the cell structures and quality on the electronic property of the cells was discussed.

Plasma sprayed coatings of Raney nickel alloys developed as electrodes for hydrogen evolution electrodes in alkaline media, exhibit poor resistance to electrochemical erosion. The aim of this work is to develop an understanding of the correlation between plasma spray process parameters and coating quality and with that improve the electrochemical performance of the coatings. Air plasma spraying with TriplexPro gun was performed using NiAlMo powders. Plasma parameters were varied and particle inflight velocity and temperature was measured by Accuraspray. Coatings were developed for conditions in which particles in-flight temperatures were comparable but in-flight velocities differed. Electrochemical tests were performed for evaluating the effect of different velocities on electrode performance. Coating attained with particles having higher velocity exhibited better electrochemical performance and durability. The microstructure and elements map before and after the electrochemical test performed by SEM and EDX show that the coatings with higher velocity particles led to microstructure that enabled better activation of the electrodes and higher surface area for reactions.

High manufacturing costs and long-term degradation are the main problems that have become a “bottleneck” and impeded SOFC’s further development. It is well known that a high operating temperature is the major cause that leads to these problems. As such, reducing the operating temperature becomes a hotspot of research. It has been reported that a uniform and dense coating can be prepared by using very low pressure plasma spraying (VLPPS) technology. The current study focuses on VLPPS for application in large-area (~100 × 100 mm) porous metal supported solid oxide fuel cell (MSSOFC), especially for the preparation of the electrolyte. It was found that the densification of the electrolyte was very good, as confirmed by the open-circuit voltage (OCV) of the cell. In the temperature range of 550~750°C, the OCV of the cell stabilized between 1.05 V and 1.1 V. The power density of the cell was also measured.

Thermal spray materials used in power generation applications are required to function within a challenging array of requirements. The coatings must be applied over typically large surface areas cost effectively, the coating must be resistant to extreme erosion and/or corrosion, the coatings must function at high temperatures and, if possible, the thickness of the coatings should be readable with standard equipment such as an Elcometer gauge. Simultaneously meeting all these requirements and advancing the alloy technology is a daunting if not impossible task if done via experiments alone or through scientific intuition. However, the design of new alloys which must possess a variety of attributes simultaneously is well suited for big data techniques. The calculation of millions of alloys and advanced data mining techniques help to quickly identify the best alloy for the application. This paper details how this process was used to design Metco 8294, a proprietary alloy. Metco 8294 is unique in that it is a Fe-based alloy of high hardness, coating adhesion, and erosion resistance, and is readable in the as-sprayed condition and after high temperature exposure.

The cold gas dynamic spraying process solves many issues with respect to the deposition and additive manufacturing of metals. Namely, it provides a reduced reactive environment, simplicity of operation, and high deposition rates. It is known that the deposition efficiency of the cold spray process can be substantially increased using helium instead of nitrogen as the process gas. However, the use of pure helium can be cost prohibitive in many situations and commercially available helium recovery systems constitute a major capital investment on top of the spray system and ancillary equipment. This work focuses on the development and use of a novel, inline gas mixing system, designed to provide a blend of nitrogen and helium at any ratio. Deposits produced with different gas ratios were investigated through particle velocity, deposition efficiency, porosity, and hardness. The experimental results show that helium, even in lower percentages, can have a significant effect on deposition efficiency and that helium percentage can be optimized to reduce the overall coating production costs. From the results, a cost model is presented which, when provided experimental values and user costs, can be used to identify the nitrogen-helium ratio that will produce the lowest overall coating cost.

Plasma spraying of large-scale components (such as paper mill rolls, rocket exit nozzles, parts of the land-based turbines for power generation, thermally sprayed free-standing tubes, etc.) and also powder spheroidization) are just several examples of industrial applications where the processing time and costs are critical. To ensure productivity and cost-effectivity of the process, it is beneficial to use plasma torches which can process high powder throughputs, i.e. with feed rates in tens of kilograms per hour. Such torches must have sufficiently high enthalpy and plasma temperature, to ensure homogeneous particle treatment and high deposition efficiency. Hybrid water-stabilized plasma (WSP-H) system with its enthalpy of more than 140 MJ/kg and plasma temperature of 25 000 K is able to process up to 40 kg of powders per hour. Since the WSP-H torch consumes typically only 15 slm of Ar at full power of 180 kW, it is a very powerful and also economical tool that meets all the prerequisites for large-scale plasma spraying applications. Spraying of three representative ceramics: alumina, zircon, and yttria-stabilized-zirconia is presented in this study. It reveals only limited influence of increasing powder throughput on particle velocity, temperature and coating microstructure. Deposition efficiency of the processes is discussed and the deposited coatings are analyzed by SEM and XRD.

Due to the growing application fields, the development of plasma generators has become increasingly important in recent years. Nowadays, DC-plasmas used for a plethora of coatings on metallic surfaces, metallization of plastic materials, surface cleaning and activation, plasma welding and spacecraft propulsion systems. The use of plasma generators for surface coating has grown enormously in the field of thermal insulation and wear-resistant coatings, especially with regard to deposition of refractory oxide ceramic layers using powders such as aluminum oxide, alumina / titania, zirconia and chromium oxide. In addition, for the plasma-assisted surface treatment, generators for both wide extended planar surfaces, as well as structures that are more complex have designed and industrially established. Nonetheless, new plasma sources still developed to provide more-efficient, tailor-made solutions due to their specific characteristics. Within this paper, a brief overview of the new innovative development of DC-plasma generator “Penta” shown. Thereby the special setup, first diagnostic results, including coatings, presented and discussed. The paper concludes with an outlook for future diagnostic measurements and possible future applications for this DC-plasma torch.