Abstract In subzero conditions; atmospheric ice naturally accretes on surfaces in outdoor environments. This accretion can compromise the operational performance of several industrial applications; such as wind turbines; power lines; aviation; and maritime transport. To effectively prevent icing problems; the development of durable icephobic coating solutions is strongly needed. Here; the durability of lubricated icephobic coatings was studied under repeated icing/deicing cycles. Lubricated coatings were produced in one-step by flame spraying with hybrid feedstock injection. The coating icephobicity was investigated by accreting ice from supercooled microdroplets using an icing wind tunnel. The ice adhesion strength was evaluated by a centrifugal ice adhesion tester. The icing performance was investigated over four icing/deicing cycles. Surface properties of coatings; such as morphology; topography; chemical composition and wettability; were analyzed before and after the cycles. The results showed an increase in ice adhesion over the cycles; while a stable icephobic behaviour was retained for one selected coating. Moreover; consecutive ice detachment caused a surface roughness increase. This promotes the formation of mechanical interlocking with ice; thus justifying the increased ice adhesion. Finally; the coating hydrophobicity mainly decreased as a consequence of the damaged surface topography. In summary; lubricated coatings retained a good icephobic level after the cycles; thus demonstrating their potential for icephobic applications.

Abstract Besides conventional industrial demands; thermally sprayed coatings are increasingly used for innovative products; such as additive manufacturing of electrical components in automotive engineering. In particular; heating units are manufactured by a combination of various spray technologies. At present; simpler spraying processes like flame spraying are investigated with regard to their suitability as a future cost-effective alternative for fabricating isolating alumina coatings. In this study; alumina cords were flame-sprayed using compressed air and argon as atomizing gases. The results demonstrate fine microstructures and a partially even higher surface and volume resistivity compared to past investigations in the literature. Furthermore; the content of alpha phase is higher than for plasma-sprayed coatings; regardless of the atomizing gas used. Moreover; flame-sprayed coatings using argon reveal a higher resistivity in comparison to coatings sprayed with air. In addition to the phase composition and kinematics; it can be concluded that humidity plays a major role in coating properties.

Abstract Developing effective heating systems to prevent ice accretion on the surface of wind turbine blades and aircraft wings is of great significance for extreme cold environments. However; due to high velocity impingement of water droplets and solid particles on the surface of these components; an appreciable degree of surface material degradation may occur. In this study; nickel-chromium-aluminum-yttrium (NiCrAlY) was chosen as a metal matrix material for a coating-based heating system. Pure ceramic powders; namely; alumina and titania; and a cermet powder; tungsten carbide-cobalt (WC-12Co); were mechanically admixed with NiCrAlY powder and deposited to fabricate reinforced metal matrix composite (MMC) coatings. The powders were deposited on cylindrical low carbon steel bars by using flame spraying. The specimens were placed in a wind tunnel to conduct a comparative investigation of their erosive wear resistance under water droplet impact. A cold spraying unit was used for solid particle impact erosion tests. The erosive wear rates were quantified by measuring mass loss. The experimentally obtained results showed noticeably lower wear rate in NiCrAlY-WC-12Co and NiCrAlY-titania coatings compared to the other coatings. The results suggest that certain MMC coatings could be effectively employed to decrease the erosion rate of coating-based heating elements.

Abstract This work is devoted to the study of peculiarities of thermal sprayed coatings behavior under conditions of cavitation, as well as the elaboration of compositions of cavitation-resistant coatings and technology for their application with the aim of engine cylinders sleeves protection from cavitation-erosion destruction. The methods of arc metallization, flame and plasma spraying were used for coatings deposition. Powders of metal alloys and oxides, mechanical mixtures of nickel alloys with carbides, wires and flux-cored wires were applied as materials for thermal spraying. Method of magneto-striction vibration was used to determine the coatings cavitation resistance. A correlation between a bond strength of coatings and the character of their cavitation destruction was established. The best results were obtained in the case of using stainless steel wires and flux-cored wires using. Resistance of coated diesel engines sleeves was increased 1.6 times in comparison with sleeves without coatings. Semi-automatic line for arc metallization of diesel sleeves with a production of 600,000 sleeves per year was designed, build up and put into operation.

Abstract The industrial flame spraying process has been analyzed by three-dimensional Computational Fluid Dynamics (CFD) simulation. The actual process is employed at the Volvo Aero Corporation for coating of fan and compressor housings. It involves the Metco 6P gun where the fuel, a mixture of acetylene and oxygen, flows through a ring of 16 orifices, while the coating material, a powder of nickel-covered bentonite, is sprayed through the flame with a stream of argon as a carrier gas by a central orifice. The gas flow was simulated as a multi-component chemically reacting incompressible flow. The standard, two equations, k-e turbulence model was employed for the turbulent flow field. The reaction rates appeared as source terms in the species transport equations. They were computed from the contributions of the Arrhenius rate expressions and the Magnussen and Hjertager eddy dissipation model. The particles were modeled using a Lagrangian particle spray model. In spite of the complexity of the system, the complex geometry and the numerous chemical reactions, the simulations produced fairly good agreement with experimental measurements. The powder size distribution was found to play a critical role in the amount of unmelted fraction of particles. The modeling approach seems to give a realistic description of the physical phenomena involved in flame spraying, albeit some model refinement is needed.

Abstract Three different types of polyethylene powders were flame sprayed onto pre-heated steel substrate previously coated by electrostatic spray system with a thin epoxy primer layer. Properties of the polyethylene (PE) powders, including powder density, particle size and melt flow rate (MFR) were measured in order to study their influence on the mechanical properties of the coating. The spray experiments started with optimization of spraying parameters. The main variables were pre-heating temperature of the substrate, temperature increase during spraying (influenced by the spraying distance), and thickness of the PE coatings. The laboratory tests performed for the coatings were coating characterization by microscopy and mechanical testing. Porosity and thickness of the coatings were determined by optical and stereo microscopy studies from polished cross-sectional samples. Hardness, impact strength, peel strength, and adhesive strength of the coatings were also investigated. Also some hot water sinking and heat cycling tests were performed. As a result from the present studies it can be concluded that powder properties have great influence on the mechanical properties of the final coating.

Abstract Improved understanding of microstructure-property relationship can help to shift from experiment-based to science-based development of thermally spray deposits. This should result in shorter and less expensive development as well as in higher functionality and reliability of the deposits. Significant amount of work has been done, however, nearly always studying deposits manufactured by only one of the thermal spray techniques. Results are therefore often spray technique specific. A broad study with samples manufactured by a number of different thermal spray techniques seems to be missing yet. Relationships valid across different techniques should provide better understanding of the generic relationships. This research employs number of different techniques - flame, HVOF, plasma (APS, VPS, WSP), to generate a wide range of microstructures. Various Ni-based alloys are studied starting from a simple chemistry (Ni) and ending with complex NiCrAlY alloys. Presented results were obtained with NiCr (80% Ni, 20% Cr) feedstock. Microstructures are characterized by various techniques-OM, SEM, XRD, small-angle neutron scattering (SANS) and others - to obtain the most comprehensive set of macro to micro structural parameters available today. The wear and corrosion properties of these deposits are measured together with internal coating stresses and the most generic microstructure-property relationships are sought.

Abstract High-velocity air fuel (HVAF) spraying was selected for spray trials of a Cr3C2-NiCr powder. To determine the effect of spray parameters on coating characteristics, particularly porosity and phase degradation, a statistical design of experiments was implemented. A wide range of statistical designs have been applied to the optimization of thermal spray coatings with a great deal of success. In this instance, a lack of prior knowledge and the need to assess many process-variable interactions efficiently led to the selection of a two-level full factorial design. High and low settings for each variable, including spray distance, traverse speed, and powder feedrate, were chosen based on the ranges typically used to spray similar materials. The resulting coatings were assessed for microhardness, porosity, residual stress, deposition efficiency, and phase transformation, after which several follow-up runs were conducted to explore trends brought to light by the initial factorial design.

Abstract Cored wires show a high potential for production of protective coatings for combined corrosion and wear applications. Iron and nickel based grooved cored wires without and with different reinforcing carbide fillers have been sprayed by arc- and high velocity combustion wire (HVCW) spraying with a Praxair Type 216 gun. Depending on the wear mechanism coatings with a similar abrasive or oscillating wear resistance like HVOF WC/Co/Cr 86/10/4 have been produced. For effective protection against oscillating wear wires with a large diameter and therefore a high content of reinforcing carbide filler have to be applied. All nickel based coatings with chromium addition show an improved corrosion resistance compared to HVOF-sprayed WC/Co/Cr 86/10/4. For coatings from wires with NiCr 80/20 velum no effect of severe sulphurous corrosion in the DIN 50018 test is observed. HVCW-spraying is especially suitable, when only a low degree of interaction between velum and filler material is wanted as for cermet-like coatings. Conventional arc-spraying rather meets the demands of a high degree of interaction between velum and filler necessary for the production of pure metallic coatings like NiCrBSi. All manufactured coatings show good machinability.

Abstract Thermally sprayed coatings of high performance thermoplastics are of interest especially for the chemical industry for anti-corrosion applications at elevated temperatures. In this paper coatings of polyetherether-keton (PEEK) and polyphenylen-sulphide (PPS) have been produced by simple flamespraying. They have been investigated by optical metallography, FT-IR analysis and DSC-analysis. Among the coating properties also the "in-flight" particles have been studied by wipe-tests and FT-IR analysis in order to assess possible decomposition effects during spraying.

Abstract Physical properties of coatings based on Fe-B, Fe-Ni-B, Fe-Cr-P-C, Fe-Ni-Si-B, Ni-P, Ni-Nb and Co-Fe-B-Si, deposited by the methods of flame, plasma-arc, and detonation spraying were investigated. The coatings have mostly the amorphous structure with the volume content of the amorphous phase equal to 75-95 %. Values of the distribution and temperature coefficients of electric resistance of the coatings, depending upon a method and conditions of spraying, as well as upon their treatment parameters, were determined. Comparative studies of these coatings and thin amorphous strips produced by the melt spinning method were conducted. The amorphous coatings of ferromagnetic iron and cobalt alloys are shown to be magnetically soft materials and are characterized by a high magnetic induction combined with a high magnetic permeability. As compared with the amorphous strips, Curie temperature of the amorphous ferromagnetic coatings is by 50-140 K higher and their anisotropy of magnetic properties is lower.

Abstract Results of macro- and microhardness investigations of newly developed coatings are presented in this paper. The coatings were produced with flame- and arc spraying technique. The coating structure and hardness is significantly influenced by the spraying method and spraying parameters. It will be shown that properties for flame sprayed coatings are more effected by parameter variations than for arc sprayed coatings. A higher hardness, a greater density and a better particle cohesion can be obtained by using the arc spraying method.

Abstract Experimental apparatus simulating a horizontal belt caster has been constructed for the study of thin strip casting of steels and light metal alloys. In this apparatus, the solidifying metal is deposited onto a moving substrate. The substrate was flame sprayed with various commercial coatings while its speed and the thicknesses of strip produced matched industrial values. The main objective of the present work was to determine the influence of various operational variables on local cooling rates and final microstructures. To this end, experiments were carried out to study the effects of various types of coating, roughness of the substrate, initial superheat, and strip thickness on heat fluxes. An interesting feature of this equipment is that the strip is subjected to different rates of cooling at the lower and upper surfaces, allowing two different rates of solidification to be studied simultaneously.

Abstract This study focuses on two major advantages of induction heating over flame heating in the treatment of coated boiler tubes. In both cases the induction heating process is simple, fast and effective. Firstly, we will show how the use of induction heating results in exceptionally thick and hard coatings with low porosity. Having high corrosion and wear resistant properties, the products can satisfy industry's needs for reliable coatings with a long service life. Next, the study will detail how a pipe with the coating already applied can be simultaneously bent by induction heating while the coating is melted and fused to the pipe. The result is a thicker, more even and reliable coating than that accomplished by the flame sprayed method on a bent pipe. The process is not only less cumbersome, but again provides a superior product for the market.

Abstract Artificial dental root materials are of great interest to medical researchers. In this study, two aluminum coating methods are investigated, atmospheric plasma and flame spraying, along with the affinity, stability, and connectivity of aluminum-based toxins. Acute toxic tests performed in vivo and in vitro show that aluminum sprayed coatings are a viable dental root material.

Abstract In this study, ethylene methacrylic acid copolymer (EMAA) was used as the matrix to produce EMAA/Al2O3 and EMAA/NiCr composite coatings from dry-blended powder mixtures. This work was conducted to determine processing concerns when using similar sized reinforcement particles of different density in a flame-spray process. This work has utility for applications that require a reduction in mechanical wear and/or to confer upon a polymeric deposit a certain functional property by the introduction of value-added powder. Free-standing coatings were produced to test the mechanical properties of the sprayed deposit. The effects of the filler content on the secant modulus, yield stress, and tensile strength are discussed. The differences in deposition efficiencies among the EMAA, Al2O3, and NiCr are highlighted with respect to particle size and density.

Abstract This paper assesses the performance of a supersonic flame spraying gun along with the quality of molybdenum coatings produced with it. The hardness of the wire sprayed molybdenum was compared to coatings made using conventional flame spraying methods. The coatings were also evaluated for porosity, bond strength, and phase distribution by X-ray diffraction. The results indicate that the supersonic gun performs better than conventional flame spray equipment when depositing refractory metals such as molybdenum.

Abstract The results of low stress, pin-on-disc and high stress grinding abrasive wear tests on coatings produced by plasma and oxy-acetylene flame spraywelding are presented. FNil5A and FNiWC35 Ni-based self-fluxing alloys were selected as typical spraywelding materials for abrasive wear resistance. The abrasive wear resistance mechanisms of welded overlays produced by various materials and processes were also characterized by hardness tests, microstructural and compositional analyses, and through analysis of the effect of different kinds of abrasive on the wear resistant of Ni-base self-fluxing spraywelding overlays. Results showed that FNiWC35 overlays exhibited improved resistance under low stress abrasion, but the relative wear resistances of FNiWC35 and FNil5A still depended primarily on the type and hardness of the abrasive medium used. For the same material, the abrasive wear resistance of oxyacetylene flame sprayed overlays was higher than that produced by plasma spraywelding. The wear resistance of the plasma spraywelding overlays depended not only on the material, but also strongly on the spraywelding process parameters.

Abstract Corrosion behavior of a flame sprayed titanium coating sealed by some resins was investigated in 3.5% NaCl solution by an electrochemical polarization measurement and an immersion test. The composition and structure of the sprayed film was also analyzed by SEM and EPMA. Although an as-sprayed titanium had no resistance to the corrosion because of its porosity, the sprayed titanium sealed with epoxy or silicon resin showed an excellent resistivity against the chloride corrosion. In spite that almost half amount of the titanium changed to oxide, nitride and carbide through the gas flame spraying, the conversion of the metal to the compounds had little effect to decrease the corrosion resistivity. The sprayed and sealed titanium coating obtained by a conventional onsite thermal spraying is expected as an economical material for chloride containing environments.

Abstract Statistical design-of-experiment studies of the thermal spraying of polymer powders are presented. Studies of the subsonic combustion (i.e., Flame) process were conducted in order to determine the quality and economics of polyester and urethane coatings. Thermally sprayed polymer coatings are of interest to several industries for anticorrosion applications, including the chemical, automotive, and aircraft industries. In this study, the coating design has been optimized for a site-specific application using Taguchi-type fractional-factorial experiments. Optimized coating designs are presented for the two powder systems. A substantial range of thermal processing conditions and their effect on the resultant polymer coatings is presented. The coatings were characterized by optical metallography, hardness testing, tensile testing, and compositional analysis. Characterization of the coatings yielded the thickness, bond strength, Knoop microhardness, roughness, deposition efficiency, and porosity. Confirmation testing was accomplished to verify the coating designs.