In this study, nickel-base superalloy coatings are deposited on CrMoAl substrates by different spraying methods and the coatings are evaluated based on their microstructure, phase composition, surface and splat morphology, bond strength, and corrosion properties. In the experiments, NiCrAlY powders with a particle size range of 30-45 μm were sprayed by conventional air plasma and a new laser hybrid plasma spraying technique. The spraying parameters are presented along with test results, observations, and conclusions. The coatings produced by laser hybrid plasma spraying had an average porosity of 0.9%, a bonding strength of 117 MPa, and significantly better corrosion properties than the APS layers.

In recent studies, crack formation was observed in oxidized areas of wire-arc sprayed Zn-Al coatings. As corrosion tests show, these cracks allow electrolyte to penetrate the coating, reducing effective service lifetime. Wire-arc sprayed coatings usually exhibit tensile residual stresses with the potential to cause such cracking. To determine the extent of that potential, the stress state of Zn-Al coatings was measured and correlated with corrosion test results. Residual stress was obtained using the sin2ψ method based on XRD analysis and the results are combined with those of previous studies, forming a hypothesis for the root cause of crack formation in wire-arc sprayed Zn-Al coatings, its effects, and its control.

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.

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.

300M steel is one of most important aerial materials, which can be used for landing gear and flap & slat track. Some surface engineering technologies are needed to be adopted on its surface, because of its bad corrosion performance. WC10Co4Cr Coatings by high velocity oxygen-fuel spray processing (HVOF) is an environmental friendly method for this protection. In this paper, WC10Co4Cr coatings were prepared on 300M by optimized HVOF processing. And their corrosion performance has been estimated by neutral salt fog test, according with ASTM B117. The results indicate that the porosity gets larger and the hardness gets higher for the dissolution of bonding phases after the test. And for the optimized coatings, there are no corrosion products in the surface and interface between the coating and 300M steel, after 2000 hours ASTM B117 test. So the coatings have a good corrosion performance.

In this investigation, different atomizing gases, arc wire spray guns, and wire sizes were used to deposit ZnAl coatings on high-strength steel substrates. Sample sets corresponding to different gas mixtures and pressures as well as other parameters were produced and the coatings obtained were evaluated based on morphology, porosity, composition, phase distribution, and oxide content. The results are presented and discussed, particularly with regard to corrosion lifetime and performance.

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.

This study investigates the formation of ZnNi/Cr 2 O 3 -TiO 2 -CuO-SiO 2 /PTFE composite ceramic coatings by atmospheric plasma spraying and assesses their ability to improve the corrosion, friction, and wear performance of reciprocating parts. The as-sprayed coatings were examined then subjected to a series of tests to evaluate corrosion and fouling resistance. Reciprocating parts that had been coated were relatively intact after 5000 h in a realistic ocean environment. Cyclical changes in coating weights were found to be influenced by the dissolution of oxide films and the accumulation of secondary products. PTFE proved to be an effective sealing agent, reducing mass loss and porosity by approximately 30%.

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.

Superior characteristics of the cold sprayed coating have led to many high-tech applications. Until recently, all these applications were carried out using ‘stationary’ systems only, while some applications such as in-situ repair of aircraft body/engine parts require a portable system. Recently a ‘Portable High Pressure Cold Spray System’ called KINETIKS 2000-2 has been developed. This system is capable of 400 C/20 bars nitrogen/helium jet, and produces dense coatings with clean interfaces of many materials. In order to establish the suitability of this process for producing aluminum alloy coatings for aerospace and other high tech industries, various aluminum alloys (CP-Al, HP-Al, 6061 Al, 7005 Al) coatings were produced over many substrate materials (2024 Al, 7005 Al, 4041 Steel, ZE41A Mg). Coatings were characterized using microstructure, bond strength, bend test, corrosion studies, etc. Microstructural study showed that dense coatings with about 2-4% porosity values were produced with clean and well bonded interfaces. Bond strength of these coatings varied between 20 to 35 MPa, Bend test results showed that the coatings have adequate strengths and could withstand severe strain conditions. Salt fog corrosion studies (ASTM B 117) showed that the coatings impart corrosion resistance to the substrates.

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).

Repair of damaged ion vapor deposition aluminum (IVD-Al) on aircraft components generally requires the use of brush plating with hazardous materials including cadmium. This paper describes a cold spray process that uses aluminum transition metals to make such repairs. The aluminum layers are applied with a handheld cold spray gun and tested according to JTP-2003 requirements for corrosion resistant coatings on steel components.

The aim of this study is to propose coatings that could potentially replace hard chromium as a means of corrosion and wear protection. Two NiCrBSi coatings are evaluated, one produced by laser cladding, the other by atmospheric plasma spraying with a post-laser treatment. Although laser-clad NiCrBSi exhibits the best technical properties, the APS coatings were found to be more environmentally justifiable based on the use of life cycle assessment (LCA) software.

Traditional metal spraying techniques, which have been used in industry for decades, such as Wire Flame and Twin-Wire Arc are classified as low velocity processes because the sprayed material is conveyed by compressed air having subsonic velocity. In order to improve the bond strength, HVAF was applied for thermal spraying for anticorrosion protection. In this paper, zinc-aluminium (Zn-Al) coatings thermal sprayed using the HVAF method are analysed. The thermal sprayed coatings were characterized by the standard techniques, such as light microscopy, scanning electron microscopy with energy-dispersive spectroscopy, X-ray diffraction, salt spray and bond strength tests. The results show that thermal sprayed coatings have a dense structure, a high bonding strength, low presence of oxides and high resistance to corrosion. This is attributed to high flow/particle velocities and relatively low combustion temperatures of HVAF in comparison with other thermal spraying technologies. High spray rate and good coating quality make the HVAF thermal spray method a viable alternative to the conventional Wire Flame and Twin-Wire Arc methods for thermal spraying of Zn-Al coatings.

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.

Titanium grade 2 as well as steel 446 and 316L powders are applied for production of X-HVOF coatings on mild steel substrates. Deposition efficiency is determined by process parameters. Microstructural investigations are carried out by means of optical microscopy, SEM and XRD. In addition comparisons of oxygen and nitrogen content in titanium coatings and powder feedstock are drawn. Corrosion protection capability of produced coatings is studied by current density-potential measurements and by salt fog tests. Depending on the process parameters increase of oxygen and nitrogen content can be restricted to factor of 2 compared to the powder feedstock. Coatings showing nearly theoretical density in metallographical inspections are possible. In direct comparison to wrought titanium grade 2 material the corrosion behavior of the titanium coatings is very promising. Keeping in mind that coatings have been produced under atmospheric conditions the observed increase of the corrosion current density by factor four is regarded an excellent result. During the corrosion tests no damage, neither to the surface nor the substrate - indicated by rust precipitates on the specimen surface, is observed. So penetration of corrosive medium to the substrate is securely avoided.

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 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.

Arc spraying has always been the most cost-effective way of thermal spraying metal alloys but oxide content and degradation of the alloy by loss of particular alloying elements have limited quality of the coatings. In this paper a process is described which greatly reduces degradation and improves coating density and oxide content. Corrosion behaviour both in aqueous and high temperature environments is markedly improved. For aqueous applications coatings of Inconel 625 were tested in a potentio-dynamic cell and by salt spray testing to evaluate both the inherent properties and the permeability of the coating and significantly improved behaviour was found in both cases. For high temperature corrosion, samples of FeCrAl were tested in air and in a sulphidising environment with and without thermal cycling. Coatings of NiCrAl and NiCrTi were also examined. The coating types and test regimes were aimed at specific practical applications such as fireside corrosion in boilers and waste incinerators, hot oxidation of flare stack burners etc. In the aqueous situation valves and process vessels are being examined as candidate applications for Inconel 625 coatings.

A study was carried out on the corrosion resistance of the JP- 5000 coatings of Superalloy 625, WC-12%Co, WC-17%Co, WC-10%Co-4%Cr and Cr 3 C 2 -25NiCr materials and comparisons made with chrome plating. The coating corrosion resistance was evaluated using the standard salt fog test (ASTM B117) and also by submersion tests in 10% FeCl 3 solution (ASTM G48), in 10% HNO 3 and in 0.1M H 2 SO 4 + 0.2M HCl solutions. The coating corrosion mechanisms in relationship with the coating microstructure and phase constitutions are discussed. The test results show that the HP/HVOF coating corrosion resistance can be significantly improved through spray parameters and coating structure optimization. All coatings tested herein having optimum microstructure and phase constitutions have shown improved corrosion resistances in comparison with chrome plating.