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.

An innovative hybrid process which combines the two very effective solid-state techniques of cold spraying (CS) and friction stir processing (FSP), was proposed to fabricate a high-strength ultrafine-grained Cu-Zn coating. Results show that the CS coating had an elongated microstructure with 78.42% of low-angle grain boundaries. Following FSP, there appear ultrafine grains with 90.47% of high-angle grain boundaries and a composition of α, β' and γ phases while the CS coatings was mainly α. Significant mechanical properties enhancement is achieved, i.e. with the ultimate tensile strength increasing from 87.2 MPa to 257.5 MPa and fracture elongation increasing from 0.17% to 0.81%. The precipitates have a significant effect on the fracture behavior of FSP coatings.

Sealants are widely used in order to enhance the performance of porous thermally sprayed coatings, e.g. for electrical insulation or corrosion protection. In order to accomplish required properties, a good infiltration is necessary. The methods to assess the success of a sealing often rely on determining the infiltration depth by SEM or adding colour pigments to the sealer. In this study, a new approach for assessing the success of a sealing operation is investigated. The underlying assumption is that porous coatings are not gas-tight and by sealing them, the measurable gas flow can be reduced. Therefore, the success of a sealing operation may be assessed by comparing gas flows at defined conditions prior and subsequent to sealing. This hypothesis is investigated by coating special highly porous substrates with a wide range of coating porosities and thicknesses, sealing these coatings, comparing nitrogen flows at a defined pressure prior and subsequent to the sealing operation and correlating the measured changes of nitrogen flow with traditionally assessed infiltration depth and filling degree.

Coating adhesion has a major effect on the performance of thermal spray coatings and is in large part determined by the chemical, physical, and mechanical properties of the substrate surface. This paper reviews some of the work that has been done to optimize the surface of different materials for thermal spraying. It covers a number of substrate preparation methods, including grit blasting, laser ablation, laser surface texturing, and dry ice blasting, and explains how different process variables affect surface roughness and bond strength.

This study evaluates the effect of hammer peening on the wear behavior of cermet coatings. WC-FeCMnSi coatings were produced by twin wire arc spraying and post-treated on a five-axis machining center equipped with pneumatic peen. The surface topography of the peened coatings was examined and compared to as-sprayed and polished samples. Dry sliding friction and abrasive wear tests showed that the treated coatings had lower friction coefficients, but were less wear resistant than non-treated samples. Likewise, strain hardening effects revealed by nanoindentation testing were offset by process-induced cracking of embedded carbides, which contributes to break-outs and third-body wear.

This study investigates the influence of heat treatment on the oxidation resistance of thermal barrier coatings. The coating systems examined incorporate an APS YSZ topcoat and a HVOF NiCo bond coat. Isothermal heating tests were conducted to determine how heat treat sequences affect interdiffusion between the bond layer and substrate and the microstructure of the bond coat and ceramic topcoat. Before and after heating, specimen cross-sections were studied by SEM and EDX analysis. Preliminary results indicate that the oxidation resistance of YSZ-NiCo coatings can be improved with a suitable heat treatment, in some cases, extending elevated-temperature service life by as much as 500 h. Abstract only; no full-text paper available.

Although research has been reported on pre and post processes for cold spraying, quantitative results are lacking. This study aims to quantify the effect of pre-coat grit blasting and post-spray stress relief and annealing treatments on cold-spray coating microhardness, bond strength, and microstructure. It was found that stress relief treatments reduce hardness, but have little effect on adhesion. Annealing also reduces hardness, but is shown to significantly improve adhesive bond strength. Grit blasting, on the other hand, was found to have a detrimental effect on tensile adhesion strength with little impact on coating microhardness.

In this work, steel columns are metallurgical bonded to tempered glass with the aid of atmospheric plasma spraying and low-temperature soldering. Glass surfaces were sandblasted using different grain sizes, then multilayer (Al 2 O 3 -Cu) coatings were applied at various power levels and spraying distances. Sn-Ag-Cu solder paste was then painted on the metallized glass and steel structures were set in place and soldered in a reflow oven. The interfacial bond strength of the alumina layer was measured along with the strength of the solder joint. The results are presented and correlated with sandblasting grain size and spraying heat input.

Residual stresses arising during high-velocity oxyfuel (HVOF) spraying usually impose a limit on coating thickness. In this work, dry-ice blasting is used in combination with HVOF spraying to produce thick WC-Co coatings characterized by compact microstructure, crystal refinement, high hardness, and excellent sliding wear resistance.

In this study, gas- and water-stabilized plasma torches were used to spray cesium-doped yttrium aluminum garnet (Ce:YAG) on different substrate materials and in large-area free-standing layers. The coatings were evaluated based on microstructure, crystallinity, and thermal stability, and tests were performed to measure porosity, hardness, phase composition, band-gap energy, and the presence of defects. Some coatings were also heat treated to determine how it changes their spectral response. The results of the examinations and tests are presented in the paper.

Thermal spraying produces coatings with relatively rough surfaces compared to other deposition methods. In this work, NdFeB coatings were deposited on stainless steel by plasma spraying at various standoff distances. Some of the coatings were also annealed. Surface roughness profiles of as-sprayed and heat-treated coatings were measured by contact profilometry and analyzed via statistical methods. The effect of standoff distance and annealing on roughness is discussed along with the significance of measurement direction and evaluation length.

In this present work, investigators determine how particle temperature, combustion pressure, and heat treatment affect the porosity, oxide content, and tensile properties of warm-sprayed titanium. Coatings were deposited with nitrogen flow rates ranging from 0.5 to 1.5 m 3 /min and combustion pressures of 1 and 4 MPa. Optimal coating properties were found for specimens formed at a nitrogen flow rate of 0.75 m 3 /min and a combustion pressure of 4 MPa. Post-spray heat treatment was found to improve bonding between deposited particles, significantly increasing the strength and ductility of the titanium coatings.

This study evaluates the influence of shot peening on the fatigue life of cold spray aluminum alloy 6082 coatings. A pneumatic blast machine with standard steel shot was used to peen both uncoated and coated substrates. Six test groups representing different treatment protocols were characterized in terms of residual stress, roughness, and rotating bending fatigue. The results show that the best fatigue performance is obtained by intense shot peening prior to cold spraying. Post-treatment shot peening, in contrast, had a detrimental effect as a large portion of the kinetic energy is absorbed in the coating, resulting in surface damage rather than further work hardening.

Alumina-zirconia ceramic material has been plasma sprayed using a water stabilized plasma torch (WSP) to produce free standing coatings. The as-sprayed coatings have very low porosity and are mostly amorphous. The amorphous material crystallizes at temperatures above 900 °C. A spark plasma sintering apparatus has been used to heat the as-sprayed samples to temperatures above 900 °C to induce crystallization while at the same time a uniaxial pressure of 80 GPa has been applied to the their surface. After such post-treatment, the ceramic samples are crystalline and exhibit very low open porosity. The as-sprayed amorphous materials also exhibit high hardness and high abrasion resistance. Both properties are significantly improved in the heat-treated samples whose microstructure is best described as nanocomposite with the very small crystallites embedded in an amorphous matrix.

The effect of the hardness in the substrate surface blasted by a grit blasting process on the adhesive strength of Zn-Al sprayed coatings is investigated to find the adhesive strength is improved by work hardening of the substrate surface. The adhesive strength between a substrate of a carbon steel and sprayed coatings of Zn-Al alloy sprayed by a wire flame spraying process is measured. The substrate is roughened by the grit blasting process with white alumina girt in various blasting angles and blasting time. The hardness is measured in around 20 micro-meter depth from the substrate surface. The adhesive strength increases with increasing the hardness even if the surface roughness is almost same. There is the definite correlation between the adhesive strength and the hardness rather than the surface roughness.

Over the year’s polymers have been used in thermal spray coatings. The most known usage is as a polymer used to seal porosity in thermal spray materials. The sealers mostly used do not really work because they do not penetrate very far into the coating. Once the coating is machined or ground the sealer is gone and we have a porosity coating due to fail. One major sealer resin system used, is Phenolic as the resin, that resin is older than most of the audience and loaded with flammable acetone. It also is not a high temperature material nor does it last long since it is a rigid material and does not expand or contract. The old sealers mostly had solvent systems in them and were replaced with a water born polymer. However, our industry has not kept up with the technology of resin based systems. Water systems sound good environmentally but it does not penetrate and really does not work well for this application. Later polyester was used with a ceramic filler to produce an abradable coating for the seal area for turbine applications. More recently higher temperature polymers were used to create a high temperature abradable coating. I want to show you some new polymeric materials that have done some new applications and also recommend additional work for the thermal spray industry for improved applications using the technology of tomorrow.

Thermal spray coatings of austenitic materials are mainly used under corrosive conditions. The relatively poor wear resistance strongly limits their use. A selective enrichment of the surface layer region with carbon by means of thermochemical heat treatment improves the residual stresses and increases the wear resistance. The interstitial deposition of carbon causes strong compressive residual stresses and a high surface hardness. The low process temperature of the thermochemical heat treatment avoids the precipitation of chromium carbide, whereas the corrosion resistance is not affected. Increases in the service life of existing applications or new material combinations with face-centred cubic friction partners are possible. In the absence of dimensional change, uniform as well as partial carbon enrichment of the thermal spray coating is possible. In comparative studies between carburized and untreated thermal spray coatings, the influence of the carbon enrichment on the coating properties and the microstructure was investigated. Carburized coatings demonstrate a significant improvement in adhesive wear resistance and an extremely high surface hardness. The cross section micrograph of the carburized coating shows the S-phase formation in the surface layer region. The depth profile of the carbon concentration was determined by GDOS analysis.

Ni base overlay coatings are being used to protect metallic engineering components in extreme conditions and actually traditional thermal spray deposition technologies such as Air Plasma Spraying (APS) and High Velocity Oxy-Fuel (HVOF) are mainly used to deposit these materials. However, Coldspray is receiving increased attention during the last years because of the lower spraying temperature required to deposit metallic coatings avoiding oxidation and reducing the coating porosity and the amount of residual stresses. The adhesion to the substrate and the growth mechanism of coldspray deposits are based on plastic deformation of impinging particles, so, in the case of high strength materials such as for example Ni alloys, it could be a lack in plastic deformation leading to insufficient compactness of the coating, barrier properties and high temperature resistance. Further improvements in the coatings performances could be attained by post-deposition thermal treatments to enhance coating adhesion and barrier properties. In this sense, the aim of this study is to explore a two-step way to produce high performances Inconel 625 alloy coatings by coldspray deposition followed by a laser glazing treatment. Coldspray Inconel 625 alloy coatings has been deposited onto AISI304 steel substrates. Laser glazing is performed using high power diode laser (HPDL) ROFIN-SINAR 13DS; the local thermal treatment on the coating surface induce microstructural changes which could modify and improve the coating compactness and performances. Coating morphology and microstructure has been evaluated and reported both before and after laser consolidation as a function of different laser conditions.

Thermal sprayed NiCrBSi wear resistant coating is widely used in industry life increasing of worn parts for protective coating of the metallic surfaces. The coating is based on the mechanical anchoring of the splats onto the substrate surface and thermal integration among the splats in the coating is not possible during the spraying process due to the operation temperature, which is lower than the melting temperature of the coating material. This, in turn, results in the formation of non-homogeneous structures and voids in the coating. One of the techniques to avoid such situations is to integrate the splats through the controlled melting. This can be achieved through the laser melting process. In the present study, laser melting of thermal sprayed coating is modeled to determine the melt layer thickness. A lump parameter analysis is introduced in the model study and simulations are carried out in relation to the actual laser melting conditions. The melt layer predicted is compared with the experimental measurements. The micro structural analyses prior and post laser melting process are carried out using SEM and XRD, and the mechanical properties such as hardness, were also investigated. It is found that the predictions of the melt layer are in good agreement with experimental results.

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.