Three Fe-based powder alloys, Höganäs Fe SP529, Fe SP586 and 6AB, have been deposited by HVOF and HVAF spraying onto mild steel plates. The sprayed samples were first ground and then shot peened using glass shot in order to seal the surface interconnected pores and other surface imperfections. The samples as ground and ground/glass shot peened were tested by salt spray (fog) exposition for 238 h according to ASTM B117/ISO 9227. FeSP586, HVOF and HVAF sprayed and glass shot peening samples achieved surface sealing enough to pass the test with appearance rating RA = 9 according to ISO 10289. All other samples achieved moderate to excessive pitting and/or moderate to excessive staining types of corrosion defects.

Ductile iron pipes (DIP) have been used worldwide since 1960s for water transmission and distribution mains. By 1979, ductile iron pipe largely replaced cast iron as the predominant material in water industry. Zn and Zn/Al 85/15 coatings applied by thermal spray technique are used for the protection of the ductile iron pipe against corrosion in heterogeneous soil conditions. In this study, heat treated and non-heat treated ductile iron pipe samples were coated with Zn and Zn/Al 85/15 in optimum spray parameters by twin wire electric arc (TWEA) spraying technique. The coatings were investigated by optical microscopy, scanning electron microscopy (SEM), and analyzed by energy dispersive spectrometer (EDS). Both Zn and Zn/Al 85/15 coatings showed fairly good lamellar structure with acceptable amount of internal porosities and oxides. Annealing oxides available on pipe surface helped the bonding of coatings. The protection performance of the coatings was compared with accelerated corrosion (salt spray) test according to the ASTM B 117 and corrosion products were analyzed by SEM and EDS technique. Salt spray test results showed that Zn/Al 85/15 coatings have better corrosion resistance than Zn coatings and annealing oxide on ductile iron pipe acts as a good corrosion resistant protective layer.

This study assesses the corrosion performance of aluminum-manganese (Al-Mn) coatings deposited on 42CrMo4 steel by atmospheric plasma spraying and (APS). Al-Mn alloy powder containing 25 at% Mn was gas atomized under nitrogen atmosphere using pure Al and Mn as starting materials. The powder was characterized by laser granulometry and SEM-EDX analysis. A fraction with particle sizes ranging from 10 to 60 μm was used as the feedstock powder. The APS coatings were characterized by optical image analysis, Vickers hardness measurements, and salt-spray testing. The Al-Mn coatings exhibited significantly higher hardness in comparison to pure aluminum. Red rust appeared after 240 h of salt-spray testing, leading to local coating detachment after 1000 h. The corrosion attack starts at coating defects such as microcracks, which can be attributed to the brittleness and nonuniform melting behavior of the powder and possibly inhomogeneities in the spraying process.

Zinc coatings are widely adopted for cathodic corrosion protection. Mostly the process of choice is hot-dip galvanizing but due to limitations regarding component size and composition of the galvanizing bath it is not always practicable. In the present paper zinc coatings alloyed with Al, Sn, Mg and Cr are applied by twin wire arc spraying to enhance the corrosion protection ability of zinc thermal sprayed coatings. The alloys were characterized and investigated using salt spray test and by means of electrochemical corrosion. Corrosion damage and products were investigated by optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS) and electron probe microanalysis (EPMA).

This paper describes an initial development of oxidation resistant coatings for SOFC (solid oxide fuel cell) interconnectors using LaSrCoFe oxide (LSCF, (La 0.6 Sr 0.4 )(Fe 0.8 Co 0.2 )O 3 ). The process involved the development of hermetic coatings using a HVOF (high velocity oxy-fuel) spray process, specifically a θ-gun spray process. The X-ray diffraction of the powder and the coating is analyzed at first. To get the hermetic coating, numerous process parameters were chosen using design of experiments (DOE). The hermeticity of the coating was tested using a salt spray test. After these tests, a hermetic LSCF coatings was obtained with virtually no interconnecting pores.

The microstructure of arc sprayed stainless steel 316L coatings appears mainly in bright white matrix, deteriorated layers (grey), and black pores under optical microscopy. The black pores and the chromium-depleted areas in the deteriorated layers are known as the factors for decreasing the ability of protecting substrate under corrosive environments. Results of experiments in this paper suggests, in the condition of this study besides the factors mentioned above, Fe-Cr oxides should be another factor of dominating the corrosion resistance in the coatings. It also describes that the quantity and the distributions of such oxides are great influence on the corrosion behaviors. In this study, two kinds of coatings were used, one with thick deteriorated layers and another with thin deteriorated layers, which were sprayed on mild steel substrate by air atomization and nitrogen atomization respectively. Salt spray test and salt-water dip test were carried out to investigate corrosion behavior in macro and micro view. An effect of sealing treatment on the performance of the coatings was also examined. Results of metallographic examination and image processing analysis are well supported by a detailed investigation of corrosion behaviors of individual phases.

This paper evaluates an electrochemical mapping method for determining the corrosion resistance and structural integrity of thermally sprayed coatings. In the test setup, a potentiostat is suspended over the test sample, forming an electrochemical cell. The circuit is completed through an electrolyte-containing porous tip. Capillary forces keep the electrolyte on the surface of the tip, preventing transfer to the substrate surface. In the investigation, electrochemical, spatially resolved measurements are carried out on flame and vacuum plasma sprayed nickel-base coatings and compared with the results of salt spray testing. It is observed that the new method offers many advantages being faster, nondestructive, and quantitative in nature. Paper includes a German-language abstract.

This report presents results of a new technology that looks promising to apply high quality corrosion resistant coatings in limited special areas. This technology could minimize or eliminate maintenance activities experienced today with existing corrosion preservation management systems. Four passivation coatings (aluminum, zinc, 85Zn- 15Al, and 55Al-45Zn) were deposited and evaluated using the Cold Spray process. The composite powders were not chemically alloyed but mixed by weight percent (powder alloyed) to prepare the composite mixture. Each coating was deposited with both nitrogen and helium gas. Deposition efficiency measurements were made for each powder/gas combination. Coatings were applied to DH-36 steel specimens and analyzed for quality of the bond line between the coating and substrate, porosity, bond strength, weight percent of metal constituents resident in the composite coatings, and integrity of the coating after 1000 hours of exposure to accelerated salt spray testing. Cold sprayed results are compared with specimens sprayed with aluminum using the flame sprayed process. Cost comparisons are made for depositing the various powders using both Cold Spray and flame spray processes.

In this paper, Ni-based cored wires were prepared by using NiCr strip to wrap metal powders of Ni, Cr, Mo, CrB. Ni-based coatings were prepared by electric arc spraying process. The microstructures of Ni-Cr-Mo and Ni-Cr-B coatings were investigated by means of scanning electron microscopy (SEM) and energy-dispersive analysis (EDAX) and X-ray diffraction (XRD) analysis. The coatings have compact surface and presented the bonding strength higher than 40MPa. Corrosion-resistance performance of coatings was evaluated by salt-spray- test and electrochemical corrosion test. The results showed that Ni-based coatings containing Mo (5%) element or B element (2-4%) had better anti-chlorine ion corrosion performance than that of Ni-based coatings without Mo element, and PS45 (Ni-Cr-Ti) coating. The anti-chlorine ion corrosion coatings could be used for resolving the corrosion protection problem of the equipments and piping contacting sour, alkali, salt liquid in the petrochemical engineering.

The effects of resin sealing on WC-NiCr HVOF sprayed coatings were studied using the anodic polarization measurements and the potentiostatic polarization measurements in sulfuric acid aqueous solution. Three types of coatings, without sealing, with sealing applied once and twice were prepared. Regarding the anodic polarization measurements the current densities of the coatings with sealing were less than that of the coating without sealing in the potential range of 0.1 V to 1 V (vs. Ag/AgCl, sat. KCl). According to the potentiostatic polarization measurements the current densities of the coatings with sealing were also less than that of the coating without sealing. Fe was detected in the electrolyte which the coating without sealing was immersed in on the potentiostatic polarization measurements. This meant that the substrate dissolved into the electrolyte because the coatings contain Fe less than 0.13 wt%. In addition, the coating sealed once were compared with that sealed twice. And it became clear that sealing effectively prevents substrates from dissolving and improves corrosion resistance of coating in sulfuric acid aqueous solution, which agreed with the result of salt spraying test.

In cold sprayed coatings, the technical properties are besides the coating material itself also highly determined by the integrity of interparticle boundaries and coating to substrate interface. One possibility to affect these boundaries is a simultaneous laser irradiation during the cold spray process. It is expected that laser-assisted low-pressure cold spraying could be an effective method to improve the low-pressure cold sprayed coating denseness and adhesion. The purpose of the additional energy from the laser beam is to create denser and more adherent coatings, enhance deposition efficiency and increase the variety of coating materials. In this study copper and nickel powders with additions of alumina powder were laser-assisted low-pressure cold sprayed (LALPCS) on carbon steel. Coatings were sprayed using nitrogen or air as process gas. A 6 kW diode laser or 4 kW Nd:YAG laser and low-pressure cold spraying unit were used in the experiments. The influence of laser energy on coating microstructure, denseness and deposition efficiency was studied. The coating microstructure was characterized by a scanning electron microscope (SEM). The coating denseness was tested with open cell potential measurements and salt spray tests. Results showed that laser assistance made coatings denser and also enhanced deposition efficiency.

In this study, alumina coatings are deposited by atmospheric plasma spraying and sealed using an aluminum phosphate solution containing a small fraction of alumina nanoparticles. Potentiodynamic polarization, electrochemical impedance spectroscopy, and salt spray tests are used to evaluate the corrosion behavior of both the as-sprayed and sealed coating samples. Besides improving corrosion resistance, the sealing treatments are also shown to increase the electrical resistance of the coatings, making them better electrical insulators.

This paper describes the fabrication of corrosion-resistant HDPE coatings with antifouling properties achieved through the dispersion of Cu particles. The main feedstock powder was prepared by coating HDPE particles with a 1 μm thick Cu shell via electroless plating. The coated particles were flame sprayed as a topcoat over HDPE and Cu layers that had been deposited on mild steel substrates. SEM, EDS, and XRD analysis was used to examine the coatings and feedstock powders. After neutral salt spray testing for 14 days, the HDPE-Cu coatings were found to be relatively intact. Coating samples of various types were also immersed in bacteria-containing artificial seawater for three days. Field-emission SEM showed that the attachment of Bacillus sp., which successfully colonized on HDPE surfaces, was significantly constrained on pure copper and HDPE-Cu composite coatings. Some of the proposed theories on how Cu ions inhibit the formation of biofilms are discussed.

WC-12Co coatings (with and without Ni-5Al bond coats) as well as Ni-5Al coatings were deposited on Al 7075 by HVOF spraying. The corrosion behaviour of the coatings was investigated by salt spray testing for 40 days, followed by potentiodynamic tests in a 3.5% aqueous NaCl solution, at 25, 35 and 45°C.The thicker duplex coatings (500µm) were not susceptible to pit corrosion, at any temperature. A small fraction of the thinner duplex coatings (260µm) underwent localized corrosion, only at 45°C. Ni-5Al and a small fraction of WC-12Co single coatings showed low susceptibility to pit corrosion which increased with temperature increasing and thickness decreasing. The coating system Ni-5Al/WC-12Co exhibited the highest resistance to general corrosion, which was independent of the thickness at the two thicknesses tested.

This paper compares the corrosion resistance of electrolytic hard chrome plating and HVOF-sprayed WC-Co-Cr on two steel alloys used in landing gears. Test samples were evaluated by means of salt spray testing and electrochemical measurements. Post-test metallographic examinations were conducted to investigate the failure mode of the coatings. Test results are presented along with relevant findings and observations. Paper includes a German-language abstract.

The economic use of offshore wind turbines requires a reliable and long-lasting corrosion protection. Sophisticated multilayer coating systems consisting of a thermal spray coating – mainly ZnAl15, a sealer and several layers of organic coating – have been proven to provide such protection. Damages to these duplex-coatings can, however, not be prevented necessitating on-site repair. In case of severe damages, the remaining coating close to the damage is often removed and subsequently, the duplex coating is rebuilt from scratch. In the present study, two integrated coating removal and substrate pre-treatment methods are investigated. For this purpose, duplex-systems were produced, artificially damaged by milling and afterwards treated by either grit blasting or with a rotating steel-wire brush, i.e. a Monti Bristle Blaster. Afterwards, the duplex coating was re-applied in the considered area. To evaluate the influence of the pre-treatment method on the coatings’ corrosion protection potential, a 38 week-long salt spray test was used. The test revealed a pronounced influence of the pre-treatment method on the corrosion protection potential. In case of grit blasting, no substrate corrosion could be detected. The use of a Bristle Blaster, however, resulted in coating failure and some spots of red rust.

SUS316L coatings were sprayed by a high-velocity air fuel (HVAF) system to reduce oxidation and thereby improve the corrosion behavior of stainless coatings. The effects of powder feed rate and particle size on the microstructure, oxide amount and adhesion strength of the coatings were investigated. The corrosion resistance of the coatings was evaluated by conducting salt spray tests. The oxide amount in the coatings sprayed by the HVAF process is below 7 % and adhesion strength is below 34 MPa. In comparison with those of coatings sprayed by a high velocity oxygen fuel (HVOF) system, the oxide amount and adhesion strength are decreased because the particles heated below the melting point of the alloy and insufficient softened in HVAF process. The coatings deposited are original porous, and they become denser through the impinging effect caused by the following sprayed particles. With the increase of powder feed rate and particle size, there is a tendency of reduction in oxides, and an obvious decrease in adhesion strength. Corrosion resistance of the unsealed coatings is insufficient, and this becomes notable with increasing powder feed rate and particle size. The sealed HVAF coating sprayed with the largest particles shows the best corrosion resistance.

Thermal spraying has been used to protect many steel structures from aqueous corrosion using Zinc and Aluminium, and to some extent their alloy coatings to provide galvanic protection. The lifetimes of the coatings can approach 50 years even when exposed in severe marine environments. Zinc coatings work by continuously sacrificing themselves and slowly dissipating over time. Aluminium coatings passivate more readily and form a barrier layer, the passivity makes them less able to protect damaged areas and to self heal. A new ternary coating system involving Aluminium, Zinc and Magnesium has been shown to be capable of providing both a passive barrier layer as well as being able to give galvanically active protection. Salt spray tests have shown that the resistance to red rust of these new coatings increases by 300% over similar thicknesses of the separate metal coatings. Processing by arcspray is straightforward and both adhesion and deposition efficiency are better than where Zinc is sprayed alone.

This paper evaluates four tungsten carbide basecoats produced by thermal spraying with a high speed flame spraying system as potential candidates to replace hard chrome in applications subject to abrasive and/or corrosive conditions. It investigates the potential of using WC-based cermet coatings deposited using high velocity oxy-fuel thermal spraying to replace electrodeposited hard chromium. The paper shows that WC-based thermally sprayed coatings are available to replace hard Cr in many applications. Salt spray tests and electrochemical measurements in synthetic sea water showed that the Cr-containing coatings had the highest corrosion resistance. These results indicated that 10Co-4Cr-WC could be the best coating candidate for conditions in which both abrasion and corrosion are present. Paper includes a German-language abstract.

A modified stainless steel coating, named as M-SUS here, was prepared by the air plasma spray process (APS) and the high velocity flame spray process (HVOF) and compared with a conventional stainless steel (JIS: SUS316L). Anodic polarization tests using NaCl, HCl solutions, neutral salt spray test, and exposure test in actual tank for HCl storage were employed for the evaluation of corrosion resistance. Structure of the coatings was investigated by use of optical microscope, scanning electron microscope, electron probe micro-analyzer, and transmission electron microscope. It was found that the coating M-SUS exhibited a remarkably superior corrosion resistance by all tests mentioned above, compared with the conventional ones. Although both of the coatings compose of gamma-austenite (γ-Fe) and delta-ferrite (δ-Fe) phases, the coating M-SUS reveals much less oxide with chromium and more delta-phase enriched with molybdenum. Another exposure test using a mixed acid of 25%HNO3 and 75%HCl yielded that the δ-Fe was not etched out but the γ-Fe vanished, that is, the δ-Fe of M-SUS has a strong anti-corrosion property. It is considered that the superior corrosion resistance of coating M-SUS is attributed to the extensive formation of anti-corrosive δ-Fe and inhibition of chromium depletion resulting from oxide formation.