Cold spraying is a semi-empirical method in that spray parameters must be optimized experimentally in regard to coating quality and deposition efficiency. In this work, porosity and deposition efficiency are the key parameters in the optimization of corrosion-resistant zinc coatings produced by high-pressure cold spraying. The deposition process is described along with the tests used to assess the morphology, adhesion, and anticorrosion properties of the coatings obtained.

The coatings of zinc and its alloys are broadly used to prevent the rusting of substrate surfaces such as steel. Cold gas dynamic spray (CGDS) is an innovative coating technique in which the deposition of solid powder particles depends upon the kinetic energy of the particles rather than thermal energy. Therefore, application of cold spray is to provide superior rust resistance by depositing more materials, formation of passivation layer, and cathodic protection. In this study, numerical investigations on zinc micro and nano size particles in CGDS were carried out. The height of the injector, the expansion ratio and the diameter of the inlet of the de-Laval nozzle was varied systematically by optimizing the stand-off distance using the two-dimensional axisymmetric models of CGDS, to study their effects on the velocity and the distribution of the particles. Prediction of the deposition efficiency was carried out using the various critical and erosion velocity models.

By means of In-Mold-Metal-Spraying (IMMS), wire arc sprayed metal coatings are transferred onto plastic parts during the injection molding process for the efficient production of metallized plastic parts. One potential field of application of IMMS parts are electrical applications such as electrically conductive tracks or electromagnetic shielding. In the current study, the properties of the transferred coatings, especially the electrical resistivity, are determined. Different feedstock materials are used for the application of the coatings. In the first investigation, pressurized air is used as atomizing gas for wire arc spraying. In contrary to Zn coatings, Cu coatings applied with pressurized air have a significantly higher electrical resistivity in comparison to massive copper. One possible reason for this is the oxidation of the Cu particles during the spraying process. Therefore, N 2 and a mixture of N 2 and H 2 are used as atomizing gas to reduce the oxidation of particles. Consequently, the electrical resistivity of IMMS parts can be significantly reduced. Furthermore, spraying distance, current and pressure of the atomizing gas are varied to investigate the influence of these process parameters on the coating properties.

A design of experiments approach was used to characterize process-microstructure relationships in the twin wire arc process using zinc feed stock. Specifically, the effect of arc current, primary atomizing gas pressure, secondary atomizing gas pressure, and standoff distance on deposition efficiency, spray pattern shape, atomization behavior, coating porosity, and coating surface roughness were investigated. All work was conducted using a Praxair 8835 torch spraying 02Z zinc feed stock. It was found that primary and secondary atomizing gas pressure significantly affected spray pattern shape, atomization behavior, coating porosity and coating surface roughness. Arc current significantly affected spray pattern shape. Standoff distance significantly affected deposition efficiency, spray pattern shape, and surface roughness. Discussion will focus on using the relationships identified through this experiment to tune the wire arc process.

Thermally sprayed coatings of zinc, and in particular zinc-aluminium alloys, offer maximum corrosion protection for steel structures and reinforcing steel in concrete. They are primarily produced by arc or flame spraying. The surfaces of zinc and zinc alloy spray coatings can be protected by sealing top coats. This produces an optimum combination of passive and active corrosion protection and allows a service life of over 20 years. The development of new materials assumes intensive investigations. This paper provides an overview of the properties of thermally sprayed zinc and zinc-aluminium alloys as well as their microstructure and investigates the corrosion protection effect in tests and near-practical conditions.

Zn coatings have been applied on steel substrates used by Renault for the manufacturing of car bodies. We had the task to make these on-line thin coatings on smooth and non de-oiled surfaces with a translation speed of 1 m/s. Furthermore, in certain cases, these coatings were situated on a visible surface of the car body and on a precise position. The coating process must be adapted to the clean conditions of the current automotive industry. The development of this application has been focused mainly on the study of a new zinc powder grade as well as on the projection procedure which had to adapt to the constraints and to the productivity of an automotive manufacturing line. Cold Spray addresses all these requirements. Positive results obtained on the mechanical examinations, the accelerated corrosion tests and chippings tests demonstrate that such new coatings meet the specifications of the customer for this kind of processes.

Zn, Zn-Al and Zn-Mg coatings have been produced by cold spraying. By careful tuning alloy compositions and spray conditions, dense coatings are produced with a hardness of 200 HV0.01 that are up to four times harder than pure bulk Zn, thus meeting the requirements for print applications. These new developments open opportunities for producing harder and more wear resistant coatings, which may allow for the production of larger number of copies without compromising quality.

Thermal spray of Zn, Zn/Al, or Al is extensively used to make anticorrosion coatings on steel structures. Twin arc spray and wire flame spray are the two most practised processes to achieve such coatings. This paper presents measurements of particle emissions generated by these two processes. Sampling and analysis of aerosols generated by both processes have been carried out inside the exhaust ductwork using various instruments: an ELPI impactor, a CNC (Condensation Nucleus Counter), a TEOM microbalance and sampling filters allowing sampling for SEM observations. Electric arc spraying produced much more fumes of ultra fine particles than flame spraying. Aluminum spraying also produces large fume quantities compared to the Zn spraying under the same conditions. The aerosol comprised submicron particles and 95% of the numerical particle size distribution was less than 100 nm. The nanometric nature of the fume particles was confirmed by observations on the SEM. The strong dilution caused by compressed air has the effect of strongly limiting particle coagulation and, in turn, the size of the agglomerated particles. Electric arc spray has taken market share versus wire flame spray for Zn, ZnAl, or Al spraying, but this study shows that it generates much more particle emissions.

Cold spray produces superior coatings with many unique properties, which have led to many new applications of sprayed coatings. In a few applications, such as in-situ repair of aircraft body/engine parts, etc., a portable system is required. Though some portable low pressure (5 – 10 bars) systems are available, these systems have many limitations on coating materials and coating qualities. Recently a ‘Portable high pressure cold spray system’, called Kinetiks 2000, has been developed. Kinetiks 2000 system can operate at 400 °C max nitrogen temperature and 20 bars max gas pressure. A touch panel on the console is used to input and control the process parameters. A hand held gun with a filament heater and a gun body, mounted directly onto the heater, is used for manual spray. This system operates with two different powder hoppers. Coatings of many materials, including aluminum, copper, titanium, zinc, etc have been produced. Microstructural investigations of sprayed coatings have shown that good, strong, dense coatings with clean interfaces and strong bonding to various substrates can be produced. Experiments are continuing to quantify the process characteristics and record the properties of sprayed coatings.

The present work probes the deposition of metallic coatings on high fiber volume fraction carbon/epoxy polymer matrix composites using pulsed gas dynamic spraying. Well-consolidated and well-adhered coatings of zinc and copper were successfully applied and initial trials with higher melting point metals have been promising. Two key aspects of the technique are the low temperatures involved and the presence of embedded ductile particles in the substrate. The embedded particles promote adhesion and eliminate the need for surface preparation procedures along with associated risks. The hardness and porosity of the zinc coatings deposited on polymer matrix composites were found to be comparable to that of similar coatings on metallic substrates.

Twin wire arc sprayed Zn, Al and Zn/Al 85/15 coatings were investigated for comparison of their corrosion resistance, electrochemical behavior. The Zn, Al and Zn/Al 85/15 coatings possess prominent electrochemical passivation behavior. Oxide formation mainly onto the coating surfaces were identified with energy-dispersive X-ray analysis and were believed to be responsible for the passivation phenomena observed in the electrochemical polarization. Zn and Al are more negative in electrochemical potential than iron. Zn coatings act as a sacrificial anode and providing cathodic protection. Aluminum shows passive corrosion protection according to stable oxide layer occurs on coating surface. Zn/Al 85/15 coating show two corrosion protection mechanisms together. In this study, steel samples were coated with Zn, Al and Zn/Al 85/15 in optimum conditions by wire arc spraying technique. These coatings were investigated behaviors of polarization and corrosion resistance with electrochemical test.

Zn and Zn/Al coatings were manufactured by using twin wire arc spray (TWEA) system under various gas pressure and current. Microstructure, hardness, surface roughness and adhesion strength of the coatings were investigated by using standard characterization methods. Test results show that increasing atomizing gas pressure increased mechanical properties and surface quality. The process current had an important role on microstructural, mechanical properties and surface quality.

Hydrogen embrittlement in high strength marine structural steels can occur by improper cathodic protection. In this article the possibility of Hydrogen embrittlement (HE) in high strength steels caused by zinc and aluminium thermal sprayed (TS) coatings has been considered. Provided potential from the TS coatings in marine environments and permissible potential for performing cathodic protection and inhibiting HE has been described. Also effective parameters on HE and prevention methods for HE by thermal sprayed coatings has been reviewed. An effective method for quality stabilizing and potential regulating in anticorrosion TS coatings is utilization of the alloyed materials. Most used material for anticorrosion TS coatings is aluminium that provides relatively moderate potential and low current density and in particular situation can cause HE.

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.

Cold spraying is quite a new process, which is an effective method to deposit dense and pure coatings. The aim of this study was to investigate microstructures and mechanical properties (hardness and adhesion) of the cold sprayed coatings. The coating materials were aluminium, copper, nickel and zinc. The substrate materials were carbon steel and copper. Influence of heat treatments on mechanical properties was studied, especially different heat treatment times and temperatures. The hardness of the cold sprayed coatings was higher than that thermally sprayed coatings and bulk materials. During heat treatment, the hardness of the cold sprayed coatings decreased and the ductility increased. Corrosion resistance of cold sprayed coatings was also studied. The corrosion resistance was tested with salt spray (fog) testing and open cell potential measurements. The corrosion tests showed some through-porosity but some parts of the cold sprayed coatings appeared to be fully dense, which showed their potential for corrosion protection.

This paper reviews the principles of cathodic corrosion protection and the different ways zinc anodes are applied to reinforced concrete through wire arc spraying. It also explains how the lifetime of zinc coatings can be extended with an organic topcoat and presents related test data. Paper includes a German-language abstract.

Structural damage caused by corrosion in concrete structures is widespread and requires extensive repair work. The installation of corrosion protection systems for constructions that are under unfavorable conditions is urgently necessary. Thermally sprayed coatings serving as anode have been developed from the cathodic protection of steel. These systems have attracted attention because of their performance and lower cost advantages, and they are about to enter the competitive anode system market. Thermally sprayed zinc coatings are applied to the surfaces of steel-reinforced concrete components that are affected by corrosion. In this article, the ability of the system to deliver a protective current is verified by field tests in a marine structure in the Arabian Gulf that was discussed in 1997. Paper includes a German-language abstract.

The use of the wire arc spray process for the production of zinc and aluminum coatings as corrosion protection represents a rapidly growing market. In this paper, the effects of various spray parameters on the performance of the process for these materials are examined. The effects of arc voltage, current, and wire diameter have been studied for their effects on the main factors affecting process performance, spray performance, and application efficiency. The results of this study have led to the development of a spray system or a power supply to maximize the performance of the process for corrosion protection applications. Paper includes a German-language abstract.

The corrosion of steel in the global reinforced concrete infrastructure is at epidemic proportions. The resulting damage is seen in highway bridges, apartments, paper mills and aquariums. In North America reinforcement corrosion in concrete bridges and parking garages generates cost estimates that range from $325 million to $1 billion per year. 1 One anode material gaining acceptance is zinc thermal spray (TS) coating. Since the first installation in 1983, zinc TSCP systems have been applied to reinforced concrete bridges, docks, parking garages and even aquariums. This paper discusses the performance of field applications of zinc thermal spray coating CP systems. The systems discussed have sprayed surface areas ranging from 280m 2 to 24,000m 2 The installations are on major concrete structures. The performance of both galvanic and impressed current systems are discussed.

Thermal-sprayed zinc anodes are used in impressed current cathodic protection systems for some of Oregon's coastal reinforced concrete bridges. Electrochemical aging of zinc anodes results in physical and chemical changes at the zinc-concrete interface. Concrete surfaces heated prior to thermal-spraying had initial adhesion strengths 80% higher than unheated surfaces. For electrochemical aging greater than 200 kC/m 2 (5.2 A-h/ft 2 ), there was no difference in adhesion strengths for zinc on preheated and unheated concrete. Adhesion strengths decreased monotonically after about 400 to 600 kC/m 2 (10.4 to 15.6 A-h/ft 2 ) as a result of the reaction zones at the zinc-concrete interface. A zone adjacent to the metallic zinc (and originally part of the zinc coating) was primarily zincite (ZnO), with minor constituents of wulfingite (Zn(OH) 2 ), simonkolleite (Zn 5 (OH) 8 Cl 2 H 2 0), and hydrated zinc hydroxide sulfates (Zn 4 S0 4 (OH) 5 xH 2 0). This zone is the locus for cohesive fracture when the zinc coating separates from the concrete during adhesion tests. Zinc ions substitute for calcium in the cement paste adjacent to the coating as the result of secondary mineralization. The initial estimate of the coating service life based on adhesion strength measurements in accelerated impressed current cathodic protection tests is about 27 years.