Biofouling has been persisting as a worldwide problem due to the difficulties in finding efficient environment-friendly antifouling coatings for long-term applications. Developing novel coatings with desired antifouling properties has been one of the research goals for surface coating community. Recently hydrogel coating was proposed to serve as antifouling layer, for it offers the advantages of the ease of incorporating green biocides, and resisting attachment of microorganisms by its soft surface. Yet poor adhesion of the hydrogel on steel surfaces is a big concern. In this study, porous matrix aluminum coatings were fabricated by cored wire arc spray, and the sizes of the pores in the aluminum (Al) coatings were controlled by altering the size of the cored powder of sodium chloride. Silicone hydrogel was further deposited on the porous coating. The hydrogel penetrated into the open pores of the porous Al coatings, and the porous Al structure significantly enhanced the adhesion of the hydrogel. In addition, hydrogel coating exhibited very encouraging antifouling properties.

This study investigates the effect of nozzle material on cold sprayed aluminum coatings produced using a downstream lateral injection system. It is shown through experimentation that nozzle material has a significant impact on deposition efficiency and particle velocity. It is proposed that the effects are related to complex interactions between particles and internal nozzle walls. The results obtained lead to the conclusion that nozzles with higher thermal diffusivity transfer more heat to particles when they make contact with internal surfaces, which increases deposition efficiency even though particle velocities are reduced.

The influence of flame spraying parameters on coating microstructure and electrical conductivity of aluminum- 12silicon coatings deposited on polyurethane substrates was studied. In order to evaluate the effect of the spray parameters on temperature distribution and its corresponding effect on coating characteristics, an analytical model based on a Green’s function approach was employed. It was found that the addition of air to the flame decreased the temperature within the substrate. Dynamic mechanical analysis (DMA) of the PU substrate revealed that the PU softened as the temperature increased. Therefore, by increasing the pressure of the air injected into the flame spray torch from 35 kPa to 69 kPa, the particles impacted a stiffer substrate. This led to increased deformation of the particles into splats upon impact, improved interlocking, and the overall coating had lower porosity and lower electrical resistance. The results obtained indicated that coating properties are sensitive to both thermal spraying parameters and temperature distribution within the substrate when depositing on elastomeric materials. The effect of torch stand-off distance on coating properties was also evaluated. It was found that higher air pressure can cool the substrate and, therefore, allow for a decrease of the stand-off distance. As a result of shorter stand-off distances, a coating with lower porosity and electrical resistance was deposited.

The aim of this study is to improve the releasability of carbon fiber reinforced plastic (C-FRP) molds by depositing a plasma-sprayed Y 2 O 3 coating on working surfaces. Composite molds are considered for use in IC encapsulation. To promote adhesion, an interlayer, either copper or gradient yttria, is applied between the substrate and coating. The coatings deposited over gradient Y 2 O 3 performed better than coatings applied over copper due to the large reduction in thermal mismatch achieved with a graded thermal expansion coefficient. Preliminary releasability results show that the yttria coatings have high adhesion strength and the potential to uniformly reduce release forces between C-FRP surfaces and epoxy resins.

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.

Nanocomposite epoxies are novel sealants developed especially for sealing metalized coatings. In order to test the corrosion protection performance of arc-sprayed aluminum coatings plus this sealer, steel panels were coated and placed in a corrosion test site on the East China Sea. Test panels were mounted in a marine atmosphere zone, seawater splash zone, tidal zone, and full-immersion zone. Several tests were conducted including corrosion and coating adhesion tests. This paper presents the results obtained from composite-coated steel panels after three years of seawater exposure.

Tensile testing of thermal spray coatings is currently covered by a variety of internal company specifications and generally by ASTM C-633. It is a highly recognized fact that liquid epoxies, on average, produce higher results in side by side comparisons with their film counterparts. However, the liquid epoxies show a higher standard deviation in those same comparisons. This raises questions about the interaction of liquid epoxies with porous thermal spray coatings. Tensile data from side by side comparisons was analyzed and optical microscopy work performed to determine how the epoxies affected the coatings and if the epoxy infiltration actually occurs. In the case of porous plasma coatings, it is shown that liquid epoxies penetrate into the coatings and, thereby, increase the apparent tensile strength.

High velocity oxy-fuel (HVOF) sprayed, functionally graded polyimide/WC-Co composite coatings on polymer matrix composites (PMC's) are being investigated for applications in turbine engine technologies. This requires that the polyimide, used as the matrix material, be fully crosslinked during deposition in order to maximize its engineering properties. The rapid heating and cooling nature of the HVOF spray process and the high heat flux through the coating into the substrate typically do not allow sufficient time at temperature for curing of the thermoset. It was hypothesized that external substrate preheating might enhance the deposition behavior and curing reaction during the thermal spraying of polyimide thermosets. An additional difficulty arises from the low thermal conductivity and low specific heat capacity of the PMC substrate, which prevent effective substrate preheating by the HVOF jet as in the case of metallic substrates. A simple analytical process model for the deposition of thermosetting polyimide onto polymer matrix composites by HVOF thermal spray technology has been developed. The model incorporates various heat transfer mechanisms and enables surface temperature profiles of the coating to be simulated, primarily as a function of substrate preheating temperature. Four cases were modeled: (i) no substrate preheating; (ii) substrates electrically preheated from the rear; (iii) substrates preheated by hot air from the front face; and (iv) substrates electrically preheated from the rear and by hot air from the front. Thermal properties of the polyimide needed for the simulations were determined by Differential Scanning Calorimetry (DSC) and Thermo-Gravimetric Analysis (TGA). Microstructural characterization of the coatings and the morphology of polyimide splats sprayed both with and without substrate preheating were analyzed using standard metallographic techniques. Coating temperature in cases (iii) and (iv) never dropped below the crosslinking temperature of the polyimide feedstock. This was the critical condition required for the curing reaction and successful deposition of thermosets by HVOF thermal spraying.

Several polymeric coatings, including flame sprayed polyethylene (PE), were evaluated for use in parts of natural gas pipelines. The components of interest were for instance large valves, T-joints, weld joints of pipes and pipe bends. More than 30 different coatings were selected to laboratory scale testing and evaluation. After first preliminary tests, the most potential coatings were selected further for more detailed and long term laboratory scale studies. After these tests were finished, one coating concept, i.e. fusion bonded epoxy (FBE) + flame sprayed PE, was prepared on a small natural gas valve body for demonstration purposes. Besides this coating concept, also some other coatings, e.g. liquid epoxy + flame sprayed PE and some polyurethane coatings were found to be potential coatings for the application. The test methods and results are presented in this paper.

In this paper, WC-Co reinforced polymer matrix coatings are sprayed on preheated steel and carbon-fiber reinforced substrates, producing relatively dense, adherent coatings. The particle morphology of the feedstock materials and the microstructure of the HVOF sprayed coatings are characterized and the thermal properties of the polymer powder and coatings are compared. It was found that the deposition and build-up of the polymer coating was only successful when substrates were preheated to the curing temperature of the thermosetting polyimide powder used. Layered coatings of varying polyimide and WC-Co content have been successfully deposited, showing that it is possible to produce graded composite coatings consisting of pure polymer at the substrate and pure WC-Co on the surface. Paper includes a German-language abstract.

Laser post-treatments and plasma-laser hybrid spraying processes are increasingly being used to extend the service life of thermal barrier coatings by making them more resistant to thermal shock. Studies show that laser-induced cracking plays a major role in the improvements achieved. The investigation of such modified layers can be difficult, however, because the stresses associated with metallographic procedures can alter the structural features of segmented microcracks and damage the specimen. In this research, laser treated and laser hybrid sprayed thermal barrier coatings are vacuum impregnated with fluorescent epoxy resins in order to study their microstructure and its relationship with thermal shock resistance. All relevant processes are described along with crack formation behaviors. Paper includes a German-language abstract.

This study investigates the effect of mounting materials on microstructure and property measurements obtained from thermal spray coatings. Various epoxies and embedding techniques are used and a wide range of layers are examined, including HVOF sprayed WC-Co, Cr 3 C 2 -NiCr, and Al 2 O 3 -TiO 2 ; plasma sprayed Cr 2 O 3 , YSZ, WC-Co, and Ni-Al; and arc sprayed copper and silicon bronze. Image analysis measurements of area percent porosity, thickness, lamellar spacing, and unmelted particles and the results of hardness tests show substantial variation relative to the method used to encapsulate soft and porous coatings. Results indicate that the ideal mounting system for thermal spray coatings would consist of a low viscosity epoxy, to maximize penetration depth, and a high cured hardness, for adequate protection of surfaces and open porosity of hard coating materials. Paper includes a German-language abstract.

Different oxides layers have been studied by friction in natural sea water medium under the same conditions (Cr 2 O 3 , Al 2 O 3 , Al 2 O 3 + Cr 2 O 3 ). The evolution of different parameters have been analyzed: friction coefficient, electrochemical potential, degradation of the layers in the contact, impedance spectroscopy. The main result observed is concerned by the cracking of the coatings under stresses, in such a way interconnection paths are rapidly present between the substrate and the sea water medium through the layers. The coating impregnation process by epoxy, before the tribocorrosion tests, improve the protection of the substrate against the corrosion.

Plasma spray deposition of epoxies under normal conditions produces coatings with low wear resistance. The research shows that the difficulty in achieving satisfactory properties is a result of the rapid heat flow from the coating to the substrate, which suppresses the crosslinking reaction. The results indicate that the use of substrate preheating or ceramic undercoats enhances the wear resistance by promoting the curing reaction during spraying.