Plasma transferred arc (PTA) is now currently used for reclamation of worn materials or to provide wear or corrosion resistant coatings welded to the base material. However, the powder injection in the molten pool created at the coated part surface is a critical parameter. In order to avoid coating reproducibility problems induced by the powder feed rate, the way to coat substrate surface with powder before the PTA treatment has been studied. As the powder cannot simply be deposited onto the substrate because of the plasma flow which would blow it off before melting it, tape casting process was used to obtain an adherent powder layer on the material surface. In this paper, tape casting of NiCu particles is described and the different organic additives used to obtain a homogeneous nickel copper film on cast iron and AG3 aluminum alloys are presented. The first results of the treatment of these films by PTA reclamation are then shown.

Mechanical coating properties like hardness, bond strength and tribological features as well as the layer composite lifetime under thermal and mechanical operation stress conditions are mainly influenced by the residual stress situation in the composite. The final residual stress state in thermally spray coated composites is superimposed by different stress mechanisms occurring during the manufacturing process. By means of the micro milling method, residual stresses are measured in a quasi-nondestructive way over the drilling depth. This paper describes the measurement features as well as experimental and numerical results. Measurements are performed on coated plane composite specimens as well as on inside coated bushing guides of aluminum crankcases for different coating materials. The correlation between residual stresses and coating properties is investigated.

The corrosion behavior of thermally sprayed Al-Zn alloy coatings immersed in NaCl aqueous solution was determined by using electrochemical impedance spectroscopy. Ohmic resistance and capacitance of the corrosion product film formed on the sprayed coating surface, and the corrosion resistance and electric double layer capacitance at the interface between the sprayed coating and the solution were evaluated. As immersion time in NaCl solution increased, the corrosion rate of the Al-2mass%Zn coating increased, but the corrosion rate for Al-6mass%Zn and Al-15mass%Zn coatings decreased due to the influence of the corrosion product.

A novel thermal spray material of MoB/CoCr with high durability in molten aluminum and/or zinc alloys has been developed to utilize for die casting parts and for galvanizing bath parts. The durability of the MoB/CoCr coatings prepared by high velocity oxy-fuel (HVOF) spraying has been investigated using a molten-metal immersing tester. It has been found that durability of the MoB/CoCr coating in the molten aluminum and Al-45%Zn alloys is much higher than that of the conventional surface treatments, such as physical vapor deposition, nitridation and spray coatings of conventional materials, such as WC/12%Co, WC/10%Co/4%Cr, Cr 3 C 2 /NiCr, Al 2 O 3 and ZrO 2 -8%Y 2 O 3 . Preservation of the crystal structure and no decrease in coating thickness due to dissolution or delamination of the MoB/CoCr coating were seen after long term immersing test of about 600 hours. Further, the molten alloys were easily dropped from the specimens of the MoB/CoCr coatings during the immersing test, suggesting much lower reactivity. On the other hand, an adhesion of the alloys on the coating surface of other specimens was clearly observed. This means that the MoB/CoCr coating is excellent in increasing the lifetime of mechanical parts, which come into contact with molten metal and/or alloys.

PTA (Plasma Transferred Arc) reclamation of aluminum alloys by hard materials with a much higher melting temperature is very difficult. This is due to the high thermal diffusivity of these al1oys. Below a critical heat flux φc nothing happens and over φc the substrate melts very rapidly contrarily to what is observed with steel substrates. That explains probably why PTA is mainly used for steel reclamation. Thus the knowledge of heat flux transferred to the anode is a critical point to develop PTA reclamation on aluminum alloys and this is the aim of this paper. An experimental set-up was built to study the heat transferred to three substrates made of different materials : cast iron for reference, aluminum alloy and copper for its high thermal conductivity. The plasma torch was a Castolin Eutectic gun and allowed to inject a sheath gas around the plasma column. The copper, aluminum alloy and cast iron substrates, easily interchangeable, were the top of a water-cooled calorimeter allowing to determine the variation of the received heat flux with the working parameters : arc current, stand off distance, plasma forming gas momentum, sheath gas composition and momentum. The determination of the arc electric field allowed to calculate the arc diameter which was compared first with pictures taken with a video camera and second, with wear traces left on the anode material. Several correlations have been established to characterize the arc voltage and the anode heat flux.

This paper investigates the effect of HVOF thermally sprayed WC-Co coatings on the cyclic deformation of the aluminum alloy 2024-T4 and the steel SAE 12L14. Strain gages are glued on the specimen surface to measure the strain response after certain intervals of fatigue cycles. The strain is also measured during the fatigue test. A calibrated beam is used to apply the bending moment and the stress calculated using the flexural formula. The stress-strain curves for uncycled and cycled specimens are determined. The dynamic strains for the coated and uncoated specimens are also monitored during the fatigue test. Paper includes a German-language abstract.

SiC-reinforced Al-12Si alloy coatings were produced using the Cold Gas Dynamic Spraying deposition process. Feedstock powder mixtures containing 20% and 30% vol. of particulate SiC were used. The composite coatings’ bond strengths and microstructures were evaluated, as well as the porosity and the SiC content. It was found that approximately 45% of the SiC particulate blended with the aluminum alloy was embedded in the coatings. The SiC was homogeneously distributed inside the Al-12Si matrix. Particle velocity measurements revealed that the addition of up to 30% vol. of SiC did not change the Al-12Si particle velocities.

In this work, Al/SiC composite coatings were deposited on the surface of aluminum alloys through atmospheric plasma spray. The effects of SiC volume in Al/SiC composite powders on the deposition behavior and the properties of the Al/SiC coatings were investigated. It was found that there were decarburization and oxidation during the deposition of pure SiC powders in the plasma flame. With the increase of SiC content, the deposition of the Al/SiC composite powder became more difficult through plasma spray. There were cracks between pure SiC and the bond coat on the Al alloy substrate resulting in poor adhesion between them. The hardness of the composite coating became higher with the increase of SiC contents. The Al/SiC(50:50) deposit with a thickness of 70 µm and a hardness of 369 Hv resulted in a strengthening and protection on the surface of Al alloy.

Aluminum alloy powders of different compositions and phases, Al/B 4 C, Al-Co-Ce, and Al 5083, were sprayed using the Cold Spray deposition process. The resulting coatings and the effects of several process parameters were evaluated using scanning electron microscopy and bond strength tests. The results show that the bond strengths depend on the powder composition but do not vary significantly with the powder feed rate. Adhesion strength values were obtained for Al/B 4 C and Al 5083 coatings. The Al-Co-Ce coatings failed at the coating-adhesive interface, indicating a superior adhesion strength than what was achieved in the bond strength tests.

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.

Aluminum castings have limited strength and stiffness and tend to exhibit brittle fracture behavior under fatigue loading. These properties can be significantly improved, however, as this study shows, by reinforcing cast aluminum parts with magnesium metal-matrix composite structures. In order to obtain a bond between the cast Al and fiber-reinforced Mg composite surfaces, Al alloy (Al 99 and AlSi 12 ) layers were deposited on the Mg structures by thermal spraying. The mechanical properties of the bonding were assessed via single-lap shear and adhesive tensile tests along with optical microsection analysis. Hybrid aluminum alloy AlSi 10 Mg castings incorporating coated Mg-MMC inserts were also produced and examined, validating the general approach, while revealing that heat input to the MMC structure must be reduced through design or process adaptations.

Aluminum coatings were deposited onto Al7075 T651 structural alloy using both cold spraying and arc spraying. Arc spray coatings were produced using optimized parameters for two atomizing gases, namely air and nitrogen. Cold spray coatings were produced using a low pressure system with air and nitrogen as propelling gases. Six surface preparation procedures prior to deposition were evaluated. Interface quality of as-deposited coatings was investigated by means of fluorescent dye interface penetration technique, bond strength testing and backscattered electron microscopy. Environmentally assisted cracking tests were performed to study the corrosion protection capability of the resulting coatings for structural applications. Micrographs of samples taken before and after cyclic load testing in salt water immersion were compared. The results demonstrated that the Al coatings produced by both arc spray and cold spray provide to Al7075 alloy a cathodic protection against cracking and localized corrosion. However, to obtain such coating properties arc spray technique required advanced surface preparation prior to deposition. For cold spray, the surface preparation has minimal influence on the coating properties thus making this process more advantageous than arc spraying for this application.

A390 alloy is a hypereutectic aluminum alloy with attractive mechanical properties at high temperature, good wear resistance and appropriate thermal properties making it challenging candidate material for automotive and aerospace applications. Currently, this alloy is widely used in automotive industry engine components production. In case of engine blocks, fatigue strength and wear resistance are the main cause of failure. Generally, the surface properties of aluminum alloys, in particular as hardness and wear resistance concerns, are insufficient to fulfill some requirements. Nowadays, there is an increasing interest toward the study and the development of innovative protective coatings suitable to enhance the wear resistance of such alloys. The goal of this paper is to develop appropriate protective coatings for A390 aluminum alloy enhancing its wear resistance. The study has been carried out to characterize the morphological, mechanical and wear resistance properties.

Cladding is a common method of providing corrosion protection of aluminum alloys, which forms an anodic layer in direct and intimate contact with the alloy sheet during cold roll processing. A structural aluminum alloy is clad in a thin layer of a higher purity alloy that is more galvanically reactive. Common examples include 1230 clad on 2024, and 7072 clad on 6061 and 7075. If this clad layer is damaged or removed the underlying structural alloy is exposed and susceptible to corrosion and/or stress corrosion cracking. Kinetic Metallization is a low temperature deposition technique compliant with MIL-STD-3021 that enables repair or replacement of worn or damaged clad layers. Aluminum or Al-Trans coatings are deposited as a new clad coating, and can be subsequently polished to the same mirror finish as the original clad surfaces. This paper presents the techniques developed for repairing worn or damaged Al clad surfaces using the economical Kinetic Metallization process and the qualification tests performed to date for various feedstock powder formulations (Ref 1).

This paper presents a way of processing cold-sprayed Ti-Al to produce titanium aluminum nitride coatings. These coatings are meant to serve as a durable protective layer on tools exposed to molten aluminum alloys. A Ti-Al powder mixture with a weight ratio of 70/30 was cold sprayed onto specially prepared substrates using nitrogen as a process and powder delivery gas. The resulting coatings were alloyed at different temperatures to obtain a stabilized Ti-Al intermetallic phase for further nitriding treatment. The nitriding process was carried out in an ammonia-nitrogen atmosphere at 900 °C. The final product had a web-shaped microstructure with the same thickness as the cold-sprayed Ti-Al. Test samples were placed in molten aluminum for 1200 hours without notable chemical reaction.

By means of homemade ultrasonic arc spraying equipment patented, under the condition of the optimum arc spraying parameters, TiAl alloy coatings were manufactured on the aluminum alloy (LY12) matrix surface. The ultrasonic arc spraying forming process and microstructure of TiAl compounds alloy coatings were investigated by the color metallurgical microscopy, SEM, XRD, EPMA and chemical composition quantitative analysis (ICP). The results showed that TiAl compounds composite coatings can be synthesized by ultrasonic arc spraying system, the coatings possess typical lamella character, consist of TiN (or TiO), TiAl, Ti 0.7.1.1 Al(N,O), Ti 2.4 Al(N,O), Ti 2.4 Al and aluminum alloy solid solution.

The Cr 3 C 2 -NiCr coatings were sprayed on an AA 7050-T7 alloy by HVOF Thermal Spray Process using AMPERIT 586.054 powder. The substrate was refrigerated during the sample preparation using liquid nitrogen in a device specially designed for this purpose. The spray conditions were also performed increasing the carrier gas flow or the oxygen flow. The XRD and SEM studies showed well-bounded coating/substrate interface, pores, metallic matrix, chromium oxides, carbides, and carbides dissolution into the matrix. The structure comparison between the samples showed a denser structure due to the increase in the carrier gas velocity and the highest carbide dissolution due to the high temperature achieved during the spray process. All samples showed similar wear abrasive behavior, and all of them showed wear rates 7 times higher than the aluminum alloy. All samples also showed corrosion resistance much higher than the AA7050 alloy in NaCl solution.

The use of aluminum in the automobile engines and other critical parts require a superior surface property of the same. This has led to the development of plasma sprayable surface coatings in the automotive components. To impart the maximum bonding strength, along with hardness to the coatings, an aluminum based composite (Al-SiC) was chosen to be the most suitable. The presence of a hard second phase within a soft matrix improves the wear resistance of the material. The metal matrix composite powders were made by mechanical alloying of 6061 aluminum alloy (particle size 40-60 μm) along with fine SiC particles (≈ 8μm). Content of SiC was varied from 20-75vol% the balance being aluminum alloy. An organic material was used as Process Control Agent to optimize distribution of ceramic within metal matrix. The coatings obtained by plasma spraying the powders were characterized for their microstructure, adherence, wear and other physical properties.

By use of homemade arc spraying system patented, which could make melted metal droplets atomized fully and make its flying velocity achieve ultrasonic velocity, TiAl alloy coatings were manufactured on the aluminum alloy (LY12) substrate surface. The slide wear resistance of TiAl alloy coatings was investigated. The effect of spraying parameters, coatings' chemical composition and microstructure on the slide-wear resistance of coatings was examined. Then the slide-wear mechanism of the coatings was discussed. The results showed that the slide wear resistance of TiAl alloy coatings by ultrasonic arc sprayed is 17 times higher than it of the aluminum alloy (LY12) substrate under the condition of dry slide-wear.

Aluminum alloy has been gradually utilized in cylinder block instead of ferrous casting material for weight reduction in automobile industry these days. In order to acquire more weight reduction, a new liner-less technology - without cast iron liner used - is putting into practice in the fields of aluminum cylinder block and the target is for diesel engine. However, diesel fuel's impurity "sulfur" element and corrosive attack risk, such as sulfuric acid generated to the surface of liner is higher than gasoline fuel. Because of such disadvantage, wear and corrosion resistances applied to the inner cylinder-bore are required in order to achieve this liner-less aluminum cylinder block. This research is intended to accomplish both wear and corrosion performances using plasma thermal spray technology and to verify the feasibility of application to actual engine bore. A newly-developed ferrous powder (Fe-C-Ni-Cr-Cu-V-B alloy) revealed extremely excellent corrosion and wear resistances, compared with currently used bulk casting materials such as Fe-C-Si-B alloy and Fe-C-Si-Mo-B alloy for cylinder liner. For the last time, the new ferrous alloy powder was applied to actual engine bore by using Rota-Plasma spray coating. The experimental results with engine bore presented potential equivalent to current engine bore.