Abstract 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.

Abstract High-velocity oxyfuel (HVOF) sprayed coatings of Cr3C2-NiCr containing solid lubricants such as nickel cladded graphite and hexagonal boron nitride were successfully developed and characterised with the aim of optimizing their friction and wear behaviour. HVOF technology was used for the integration of solid lubricants to achieve strong cohesion between particles while minimizing thermal decomposition. Coating microstructure and composition were measured and correlated to the results of tribological and corrosion tests. The integration of the solid lubricant greatly reduced friction and wear volume at room temperature, but the lubricating effect was highly dependent on atmosphere and temperature. Cr3C2-NiCr with hBN, however, tends to exhibit more stable wear resistance over a wider temperature range and can be used at temperatures beyond 450 °C.

Abstract The aim of this investigations was to increase the wear resistance and the corrosion resistance of magnesium alloys. It can be noticed, that the coating of magnesium alloys is practicable with PTA welding and laser welding. The quality of coatings depends on the composition of the strap material, on the composition of the coating material (matrix material, carbides) and the welding parameters. The magnesium alloys AM50 and AZ31 are suitable for coating. But microporosity is not available. The best results were obtained with a coating matrix material of AlSi12 and addition of B4C. This coatings have a fine and homogeneous structure. Paper text in German.

Abstract Chlorine corrosion is one of the major problems in superheater tanks at power plants that use fuels containing chlorine. Reducing conditions and combustion residues also increase the rate of corrosion. High chromium HVOF nickel-based coatings are seen as a way to prevent chlorine corrosion at elevated temperatures. Intermetallic layers are also of interest in this regard. In this paper, corrosion resistance of several HVOF coatings, laser treated HVOF coatings, diffusion coatings, and boiler steels in chlorine containing atmospheres is studied. Special attention is paid to the effect of the coating composition and coating structure on corrosion. Corrosion tests are performed in two simulated biofuel combustion atmospheres. One atmosphere is oxidizing and the other atmosphere is reducing. Paper includes a German-language abstract.

Abstract This paper aims to evaluate the effect of bond coat oxidation on the coating life of three TBC systems graded, duplex, and triplex. It investigates the hot corrosion resistance of the TBC's over nickel base alloys namely inconel 617 and IN738. Thermal plasma spraying is a flexible and versatile powder consolidation method. Plasma spraying is used to deposit thermal barrier coatings (TBCs). TBC's often faces the problems of spallation and cracking in service, due to the mismatch of thermal expansion coefficient between YSZ and the nickel alloy bond coat. Hot corrosion is a potential problem in many industrial applications including gas turbines, fuel conversion and combustion units, fuel cells, incinerators, and oil refinery equipment. The TBC's were deposited over two Ni-base alloys, namely Inconel 617and IN 738 with vacuum plasma spraying machine, from plasma - technique AG, Switzerland. Paper includes a German-language abstract.

Abstract In this paper, the corrosion characteristics of two coatings of the same generic Ni-Cr-Si-B self-fluxing type applied by the High Velocity Oxy-Fuel process are assessed in the as-sprayed condition. One of the coatings is also investigated after post spray treatment with polymer sealing and after vacuum furnace fusion. The paper focuses on the effect of corrosion behaviour in terms of electrochemical measurements and observed mechanisms in relation to the coating microstructure. Microstructural characteristics and the static corrosion behaviour of the coatings are investigated. It is observed that the crack corrosion and the local attack at the lamellar boundaries dominate the corrosion in the layers in the sprayed state and in the sealed state, while the pitting corrosion, which results from the failure of hard phases, plays the main role in the melted layer. Paper includes a German-language abstract.

Abstract This paper examines 316L stainless steel and Hastelloy C coatings sprayed by a commercially available high velocity oxygen fuel (HVOF) apparatus. Structural features such as porosity, oxygen content have been measured under various spray conditions. Polished and heat-treated Hastelloy-C layers showed good corrosion resistance in all environmental conditions. Corrosion resistance of 316L stainless steel coatings sprayed by HVOF and wire- arc techniques was compared for protection of steel rebars in reinforced concrete. The paper summarizes major results obtained by the laboratory evaluation and describes the results of marine exposure test up to 6 months. The results showed that HVOF coating performed much better than the wire-arc sprayed ones because of the small amount of porosity. In the marine exposure test, it was found that tidal and immersion zones attack more severely than splash zone against these types of coatings. Paper includes a German-language abstract.

Abstract Arc spraying is the most important of all thermal spray processes when considering the annual consumption of filler metal. This method is widespread in all branches of industry and the number of applications has steadily increased. The method is attracting a great deal of attention, particularly due to the effectiveness of the process. Zinc spraying was traditionally the most important area of application for corrosion protection; the processing of aluminum, aluminum-magnesium, and zinc-aluminum has caused sensation in the area of offshore and seawater applications. However, applications in other areas have also been increasingly covered, which is what this article is about. Paper includes a German-language abstract.

Abstract This paper aims to develop a special nickel-chromium-chromium carbide cermet coating deposited by subsonic velocity flame spraying with excellent quality to resist high temperature oxidation, corrosion, and erosion in boiler environment and to explore the influence of chromium carbide fraction and sealing on the coating performance. Thermal spraying has offered a cost effective, reliable solution for boiler tube protection to extend boiler life. Plasma spraying has suffered a challenge from high velocity oxygen fuel (HVOF) technique due to its high velocity, strength cohesion, and low porosity when HOVF process has become one way to obtain high quality coatings. A subsonic velocity flame spraying can satisfy the requirements, and the coatings can be done inside the boiler or the workshop. Testing results show that various coatings exhibit different characteristics of erosion wear. Paper includes a German-language abstract.

Abstract The increasing use of thermally sprayed layers led to an increasing need for knowledge regarding the behavior of the layers in various aggressive environments. Due to the different characteristics of the layers used, the mechanisms of the layer attack vary greatly. The effect of the corrosion protection of ceramic layers is different from that of cermet layers or metal layers. This paper includes a detailed investigation of corrosion mechanisms and obstacles of different thermally sprayed layers with regard to their corrosion protection at room temperature. Paper includes a German-language abstract.

Abstract A new thermal spray technology has been proposed. Called Electrical Chemical Thermal Spray (ETCS), it combines plasma energy with the combustion gases of solid propellants to heat and accelerate particulate materials. The hybrid technology promises new degrees of freedom in materials processing over the conventional thermal spray processes by allowing thermal energy transfer to the particles and particle accelerations to be optimized separately. Experimental coatings were formed using a prototype system made from a converted ½” plasma gun fueled with double-base solid propellants to explore this novel concept. The prototype test-facility equipment was limited to single-shot mode. Examination of the coatings formed, and conceptual analysis by analogy to conventional technologies was used to assess the capabilities and limitations of the hybrid process. Impressive in-flight powder velocities of 1100 m/s were reached, with deposition yield efficiencies of 60 - 85% achieved for WC-Co coatings after first round of optimization. However despite the ability to deposit single-shot carbide and metallic coatings with thickness exceeding 200 µm. chemical degradation and extensive cracking combined to limit attractiveness of coatings as compared to those produced using commercial technologies. Unlike the oxidation effects with atmospheric plasma spray and the various low-velocity flame-spraying technologies, chemical degradation in the prototype ETCS was the result of interaction between the gases produced from the combustion of the propellant and the coating material. It is seen that the organic, nitrocellulose based solid propellants are inherently unsuitable for spraying reactive material. With suitable fuels however, it is believed that the inherent advantages of high throughput, versatility and low labour requirements are such that ETCS will have commercial advantages for the coating of large structures.

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 Thermal spray committee of Japan Association of Corrosion Control (JACC) has been conducting a corrosion test of thermal sprayed Zn, Al and Zn-Al coatings at coastal area since 1985. Twelve kinds of sprayed coating were deposited onto steel pipe by arc- and flame-spraying at varied thickness and subjected to various post-spray treatment. The samples were set vertically into the seawater at a port 80 km south from Tokyo. Corrosion performance were inspected annually by recording the appearance and coatings' thickness at sea air-, splash- and tidal-zones. No significant changes were observed for five years exposure. After 7 years, however, Zn coatings with and without sealing started to suffer degradation in the immersed portion. Contrary to this, Al and Zn-Al coatings still exhibit superb corrosion performance. The test will be continued till 2001 to finish a 15 years field test. This paper reports the summary of corrosion performance of sprayed coating during the first 10 year period.

Abstract The work reported herein deals with the interaction among the thermally sprayed coatings and steel substrate in acid aqueous solutions investigated by using the electrochemical process. Thermally sprayed coatings on steel substrate for such as the tribological applications except for the sacrificial anode property have been extended. The environment of these machinery components is often utilized accompanied with the aqueous solutions. The galvanic corrosion occurred in aqueous solutions among the metals or alloys have been well known. In the actual spray process, the formation of penetrated pores or crevice defects are not generally avoided. In the aqueous solution environment, the penetrated defects cause the galvanic corrosion between coating and steel substrate, and tend to be occurred the coating spalling. In this work, the electrochemical process was employed to determine the corrosion phenomena. The preferable combination of sprayed coatings and steel substrate are discussed and the examples of design of the intermediate layers are proposed.

Abstract This paper describes and discusses aspects of the erosion-corrosion behaviour of a WC-Co-Cr, HVOF sprayed coating when subjected to an impinging jet of an aqueous solution of 3.5% NaCl containing solid particles at 18°C. Although pure mechanical erosion has been found to contribute to a large part of material degradation, a considerable amount of material loss can be attributed to the direct and indirect (synergy) effect of corrosion. Aspects of the influence of time, solids loading and impingement angle have been investigated and the mechanisms of erosion-corrosion are discussed.

Abstract Structural damage in concrete structures caused by corrosion is widespread and demand comprehensive repair work. The additional installation of an active corrosion protective systems for structures being located in unfavourable conditions is imperative. Thermally sprayed coatings serving as anode have been adapted from the cathodic protection of steel. These systems have gained attention as they offer advantages in efficiency and lower cost. Thermally sprayed zinc coatings are applied to new steel reinforced concrete structures or those which are subject to re-structuring. In this contribution, the capability of various systems is examined by field tests in a marine structure and in different laboratory tests under natural and under accelerated conditions.

Abstract It is pointed out that properties corresponding to 3 to 5 % of gross domestic products are lost by corrosion in every year in advanced countries. Corrosion including oxidation is still one of the biggest technical problems which human beings are facing. The application of thermal spray coatings is one of the strongest weapons to prevent corrosion of steel and iron structures. The thermal spray coatings, however, are not panaceas to prevent corrosion. They involve many problems and it is important to understand the proper ways to apply the thermal spray coatings for corrosion resistance. In this paper, a state-of-the-art review on the science and technology against corrosion, oxidation and hot corrosion by the thermal spray coatings is presented.

Abstract The development of corrosion resistant sprayed coating without sealing is required to increase reliability of the thermal spray coating method and to expand the field of application for the wet corrosion environments. The conventional wire flame sprayed Al coating on the steel substrate without sealing has poor resistance against aqueous corrosion, so as to be restricted in use in practical fields. A duplex coating composed of sprayed Al on a 80Ni-20Cr alloy undercoat was proven to have sufficient resistance in a hot, near neutral aqueous environment through a trial use in a vegetable oil process. In this paper, mechanism of the corrosion resistance of the duplex coating is clarified by electrochemical measurements of the corrosion potential and the anodic polarization characteristics.

Abstract Zinc and aluminium coatings have been used widely to protect steel structures from corrosion in aggressive and hostile conditions. The more recent development of zinc 15wt% aluminium alloy in a wire form has demonstrated that arc-spray coatings can be produced with a resistance to red rust which is superior to that of the single metals. Competitive 'pseudo' alloy or composite coatings produced by co-spraying wires of zinc and aluminium have been shown to achieve resistance to salt spray conditions similar to this conventional alloy. Work described in this paper confirms these findings and goes on to demonstrate an additional advantage of co-spraying an aluminium -5wt% magnesium instead of aluminium with the zinc. The importance of providing a fine dispersion of the two phases in the 'pseudo' alloy is highlighted and an alternative method of providing a similar dispersion by using a 'cored' wire (e.g. Al-5wt%Mg wire in a zinc sheath) approach has been demonstrated. The importance of 'self sealing' in these coatings after the initial loss of zinc is discussed which is related to the coating microstructure and their electrochemical behaviour in chloride solutions.

Abstract The development of new spraying processes has increased the demand for high quality protecive coatings. Many thermal spraying processes have been developed to obtain coatings for a wide spectrum of materials and substrates. The High Velocity Oxygen Fuel (HVOF) process involves lower temperatures and higher velocities than those required by other techniques to obtain high density coatings. It is desirable to know which are the main factors that affect the corrosion behaviour of coated materials. The corrosion behaviour in chloride solution of a 34CrMo4 steel coated with different kinds of powder have been studied. The electrochemical corrosion of the coating-substrate system was characterised by corrosion potential measurements and potentiodynamic polarisations. Microscopic studies have also been performed by means of SEM. The corrosion tests were performed in synthetic marine water (ASTM D-1l41) in the presence of dissolved air. Polarisation resistances have been obtained from potentiodynamic studies. Measurements were carried out on two different (Ti,W)C+Ni coatings, as well as on the coatings obtained from a TiC+Ni-Ti powder which had been previously Ni coated using an electro less method. The best corrosion results were obtained from these last coatings.