Plasma arc sprayed coatings are largely developed in Perfect Circle Europe because of the wide range of coating materials which ensure numerous tribological properties. Spraying parameters are of great importance in improving the coating structure and therefore the coating wear, adhesive, cohesive and corrosive resistances. The utilized plasma gas is first studied; designed experiments are then achieved to optimize the all spraying parameters. More than the spraying parameters, the powder formulation has a major influence on the coating tribological properties. Several powders are studied with the aim to reduce the ring-liner system wear. Tests on idealized samples coupled with engine tests help us to characterize the tribological behaviour of some molybdenum based coatings.

In the Automotive Industry the need for lower manufacturing costs, the use of less strategic material, and easier, faster, and more flexible routes for manufacturing are being looked for continuously. The environmental concerns relating to the use of galvanic coatings is growing. This has led to the examination of the plasma-powder spray process for the application of coatings for surface modification. In the area of engine cylinder bore coatings a major advance is taking place in the use of a rotating plasma spray device. This paper covers the use of a plasma-powder spray process for the coating of aluminum-silicon cylinder block bores using a rotating plasma gun capable of producing coatings of reliable microstructure and integrity. Properties and microstructures of the applied coatings will be presented. Test results will be shown that the necessary bond strength of the coating can be achieved without the use of a bond coat. Surface preparation prior to coating and surface finishing methods after coating will also be discussed. Experience in Europe, Japan and the Unites States will be discussed which show that the plasma-powder spray process offers a performance proven and cost effective solution for the coating of cylinder bores, thus demonstrating the future application potential for this technology.

In this paper, RF induction plasma deposition of Yttria Stabilized Zirconia (YSZ) is studied with the objective of producing dense solid electrolyte membranes for Solid Oxide Fuel Cells (SOFC). Different RF induction plasma torch configurations were tested. The results show that high density layers could be obtained using a supersonic Laval nozzle attachment on a standard torch. Coating with apparent porosity of less than 1% could be obtained using this technique at relatively high deposition rates. Optical or electron microscopic examination of the deposit coupled with image analysis show, however, that porosity measurements using these techniques can suffer from relatively large discrepancies depending on equipment setting. A discussion is presented of the validity of this porosity measurement technique.

The central components for solid oxide fuel cells (SOFC) are the electrodes-electrolyte multilayer arrangement (PEN) and the separating bipolar plates. The PEN (Positive electrode- Electrolyte-Negative electrode) assembly consists of a dense gastight yttria-stabilized zirconia (YSZ) electrolyte and porous electrodes for which usually Ni-YSZ cermet anode and Sr-doped LaMnO 3 cathode layers are used. The various PEN units are connected in a cell stack by bipolar plates which are either metallic or ceramic ones. Furthermore, a protective layer on the metallic bipolar plates consisting of a chromium alloy is required to prevent chromium evaporation leading to a rapid and strong degradation of the SOFC performance. At the DLR Stuttgart both the DC and the RF vacuum plasma spraying technique have been further developed and adapted to meet the requirements for the manufacture of the different SOFC components. The DCVPS process using specially developed Laval-like nozzles is especially appropriate to the production of thin and dense coatings as required for the electrolyte and the protective layers. However, applying special spray parameters and nozzles it is also possible to deposit porous electrode layers. The production of the entire PEN arrangement in one consecutive DC-VPS process is the objective of the actual development. On the other hand, the RF plasma spray technique is suitable for the near net-shape production of bulk components such as the metallic bipolar plate. The development of the deposition processes for the production of SOFC components using DC and RF plasma spray methods and the results obtained concerning PEN fabrication, deposition of protective layers and the near net-shape production of metallic bipolar plates are presented in the paper.

The direct conversion of heat into electric current is still less developed form of energy conversion. Thermoelectric material working in a temperature gradient is able to induce a voltage that can drive a serial resistor. New research activities try to broaden the employment of thermoelectric generators from spacecraft technologies to terrestrial applications. The main problem at the moment is rather the lack of economic production methods, than the low efficiency of conversion. After an overview about the basics of thermoelectrics and possible applications the paper presents the thermal spraying as an alternative processing method with first attempts to realize graded structures. Al-doped and Co-doped FeSi 2 has been consolidated by APS, SPS, VPS and HVOF spraying. The microstructure, phase composition and oxygen input have been investigated and set into relation to thermoelectric properties.

Paper presents a study of modeling and numerical simulation of laser engraving process. The 1-D simulation concerned CO 2 c.w. pulsed laser engraving of plasma sprayed alumina, titania and aluminum titanate coatings. These coatings will possibly replace the Cr 2 O 3 ones used currently in manufacturing of anilox rolls. The model was refined in comparison to the previous one (1) by taking into account the speed of the roll at the engraving. The actual thermophysical coefficients of plasma sprayed alumina, titania and aluminum titanate were input to the computations. The model enabled calculation of the engraving's depth in function of the principal laser treatment parameters viz. pulse length and laser power density. Finally, the overflow effect at the laser treatment of new ceramics was discussed and compared to that occurring at Cr 2 O 3 engraving.

Results are presented of a project analysing the relationship between the production parameters of plasma sprayed self-lubricating Cr 2 O 3 -CaF 2 coatings and their structural, wear and lubricating properties. The production method consists of a preparation step where a powder blend of the matrix material (Cr203) and solid lubricant (CaF 2 ) is agglomerated, followed by atmospheric plasma spraying (APS) of the agglomerates. Selection of the most appropriate agglomeration and plasma spray parameters as well as the microstructure of the coatings will be discussed.

Plasma sprayed tungsten coatings are considered as potential candidates for materials in contact with the plasma in future fusion reactors. In this work, the thermal shock resistance of these coatings is studied to determine which of five changed deposition parameters most influences the coating's performance. The thermal shocks were generated with a pulsed electron beam gun. The pulse duration was 0.2 and 0.5 s and the absorbed power density 60 MW/m 2 . Two series of samples were analyzed. One was plasma sprayed at atmospheric pressure (AP) and the other at low pressure (LP). The LP coatings were deposited on a molybdenum alloy (TZM). AP coatings were deposited on molybdenum and on water cooled copper coupons for fatigue tests. The porosity seems to be a positive factor for thermal shock resistance. The thickness of the coatings and the spraying atmosphere were found to strongly influence the thermal shock resistance. In the case of the fatigue test, some coatings withstood up to 1000 shocks of 0.5 s duration.

High Velocity Oxy Fuel, (HVOF), is a high energy Thermal Spraying Combustion Process, producing high density coatings with hardness values in excess of 1200 VPN. Such coatings, using metal carbide spray material, are used extensively in the aerospace industry, in areas where high wear resistance is particularly important. The Linde Detonation Gun, CD-Gun'), has until recent times been the predominant system for applying these hard faced coatings. However, the advent of a number of new HVOF systems approximately 5 years ago, allowed Gas Turbine Repair and Overhaul bases the opportunity to offer a more competitive coating service, i.e. these "1st generation" HVOF systems allowed the development of comparable, if not superior coatings to these produced by the D-Gun. Having successfully developed and approved HVOF coatings for the use on Rolls-Royce Gas Turbine components for both Repair and New Manufacture, Rolls Wood Group addressed the problem of transferring HVOF technology from aerospace components to alternative markets, i.e. refurbishment of equipment used in Oil and Gas Production.

High-Z materials such as tungsten are currently considered more suitable for the inner coatings of fusion devices than low-Z materials. The VPS parameters are being optimized for different tungsten powders with respect to uniform pore distribution and distribution of unmelted particles in the coating. High process reliability is aimed at in coating production. Copper is used as the substrate material. The spray efficiencies, coating porosities and unmelted particles in the coatings are being examined and the microstructures evaluated. Spraying parameters are determined for two different powder fractions leading to relative densities ≥ 90 % of the theoretical density.

Functionally gradient composites were spray formed via vacuum plasma spray deposition using tungsten cylindrical substrates. Materials deposited included tungsten-hafnium alloys and M-2 tool steel. Some deposits included micro-laminate layering with hafiiium alloys sprayed within the tungsten-hafnium matrix. Vacuum plasma deposition was shown to provide a viable means of producing functionally gradient composites from tungsten base materials. This was determined both by microstructural characterization of deposit structures and by measuring the compressive properties of the materials. Compression testing of the W-Hf matrix composites demonstrated compression strength of 1,552 MPa (225 ksi). Compression strengths of the tungsten/steel composite averaged 1,068 MPa (155 ksi). Failure of the W-Hf samples occurred via fracture of the tungsten/hafnium matrix whereas the tungsten/steel composites failed within the wrought tungsten core.

Thermally-sprayed low-Z coatings of boron carbide (B4C) on aluminum substrates were investigated as candidate materials for first-wall reactor protective surfaces. Comparisons were made to thermally-sprayed coatings of boron, MgAl204, Al2O3, and composites. Graded bond layers were applied to mitigate coefficient of thermal expansion mismatch. Microstructures, thermal diffusivity before and after thermal shock loading, steel ball impact resistance, CO2 pellet cleaning and erosion tolerance, phase content, stoichiometry by Rutherford backscattering spectroscopy (RBS), and relative tensile strengths were measured.

Spray and Fuse coatings are ideally suited to boiler environments. The fusing step gives to optimized coatings a uniform chemistry and microstructure, a metallurgical bonding, no through porosity, a low oxide content and no cracking. The relative simplicity of the traditional processing equipment is suited to on-site and automated application including coating repair. Although enjoying considerable success in traditional boilers, their advance into new applications appears restrained by the issue of substrate property modifications during fusing. This paper studies the modification in substrate boiler tube materials (microstructure and mechanical properties) associated with the coating of advanced NiCrBSi alloys. Charpy impact, tensile strength, yield strength, elongation and thermal expansion coefficient testing between 22°C and 450°C are measured. By optimal coating design to a specific substrate, the effect on mechanical property modifications by fusing could be dramatically reduced to allow new and reliable coatings systems to be demonstrated for advanced applications. The future for Spray and Fuse coatings in boilers is discussed.

There are numerous industrial applications where materials are subjected to simultaneous high temperature oxidation/corrosion and wear (such as erosion). This combination often leads to accelerated degradation. Specific industries include: chemical, waste incineration, power generation and paper/pulp with typical applications including boilers and cyclones. Previous studies have established wrought material compositions and microstructures which can resist these environments. In searching for cost-effective industrial solutions, surface coating via thermal spray becomes attractive. However, the microstructural complexity of such coatings can make the simple extrapolation of bulk material behavior to these coatings dangerous. If these coatings are to be used more widely, a greater understanding of their high temperature erosion/corrosion behavior and the influence of coating process is required. A range of Fe-and Ni-based alloys and thermal spray techniques were studied under various high temperature erosion/corrosion conditions. The critical erosion parameters of impact angle (30° to 90°) and temperature (up to 550°C in air) have been studied in an atmospheric fluidized bed test rig environment, using Al2O3 erodent at a typical impact velocity of 4m/sec and conventional high temperature erosion test equipment. The important microstructural and mechanical features of the coatings and the effect of the thermal spray process are discussed in terms of their high temperature degradation mechanisms.

Many thermal spray coatings provide excellent wear and corrosion resistance, while providing die same surface finish offered by chromium plating. In the past, the choice between thermal spraying or plating was usually based on part size, area to be coated, cost and familiarity with one or the other method. Today, the thermal spray processes are showing greater popularity due to: ♦ New thermal spray processes and coatings with better properties ♦ Increased chromium plating costs due to stricter regulations on the process and the disposal of its waste products ♦ The closing of chromium plating facilities Thermal spraying offers an opportunity to select a coating from a wide variety of processes and materials that will meet the specific requirements of each application. While this may cause some difficulty in selecting the optimum coating, the selected thermal spray coating often has superior propolies and/or lower cost compared to chromium plating. The highest quality coatings are sprayed by the HVOF process, many with carbide containing materials. Dense plasma grayed ceramic materials offer good wear resistance plus elevated temperature capability. The most economical replacements for chromium plate are applied by the two-wire arc spray process. This paper examines the properties and costs of eight different dismal sprayed coatings and compares them with electroplated chromium.

High temperature corrosion is a serious problem on tlie heat exchanger tubes of recuperators because they encounter an corrosive environment at maximum temperature around 900°C. These tubes were found to be corroded via oxidation, sulfidation and molten salt corrosion. Particularly molten salt corrosion could be the most severe corrosion mechanism. As a protective coating for recuperators, nickel and cobalt based self-fluxing alloys, iron based amorphous alloy and chromium carbide cermet coatings were considered. These coatings were prepared by an arc spray and or/not fusing or a HVOF spray. Their molten salt corrosion resistance was tested, and the high temperature corrosion resistance in a SO2 containing atmosphere was examined. Also microstructures of the coatings were studied after corrosion tests.

When buildings are subjected to earthquakes, dampers are effective in decreasing their failure by absorbing the input energy. An object of this study is to develop a new type of friction damper, on whose faying surface aluminium is sprayed, and the double friction joint is tightened with a high-strength bolt. When slip occurs on this friction damper, the slip coefficient is high and comparatively stable. Specimens of the friction damper were tested under the dynamic repeated loading condition to investigate the effect of the condition of the faying surface on the dynamic hysteresis characteristics. The parameters of the test are the type of sprayed metal, the sprayed side of the plate(s), thickness of sprayed metal, the finish of the sprayed surface, and initial clamping force (contact pressure). Results indicate that there exists the condition of suitable characteristics of a metal sprayed friction damper.

This paper deals with the problem of feeding hot billets into roll stands for rolling into different shapes and the need to apply a traction coating to the roll surface at the passes so that the rolls grip the hot billet. Steel mills have tried different methods over the years to make the roll surface at the passes rough, from throwing a shovelful of sand as the billet is entering the pass to knurling and embossing a rough pattern on the passes with a pepper chisel. Some mills have tried to use sand blasting on the rolls as the billet is passing through and thus ruining the bearings. The process used for this paper is spraying a 0.006" to 0.008" thick coating on the passes with Bondrite, an 80-20 Nickel Aluminum composite wire manufactured by us. The application of this coating is extremely easy and fast. The only preparation before spraying is to clean the roll surface with a good solvent that does not leave any residue. Bondrite has a very high bondstrength and bonds to the clean smooth surface of the rolls with enough bondstrength to impart a rough traction coating on the passes.

Ultrasonic propagation characteristics in thermal spray materials are affected by the complex microstructures of these coatings. Factors such as oxide stringers, porosity, splat size and morphology can all affect wave propagation. This dependence causes many concerns when one performs nondestructive evaluation of such coatings. However, we find that the unique properties of thermally sprayed coatings can be used for the fabrication of the cladding region of clad solid ultrasonic wave guides (or buffer rods) consisting of a core and a cladding. These wave guides are used as precious quality control devices for on-line monitoring of industrial materials processes. This paper is devoted to the tailoring of the ultrasonic behavior of metallic coatings produced by arcspraying. Experimental results show that by a proper control of the core-cladding system it is possible to minimize ultrasonic spurious signals occurring in a clad wave guide while the tailoring of the splat morphology, intersplat oxidation and porosity enable the appropriate ultrasonic absorption within the coating. The unwanted spurious signals are normally generated at the periphery of the core. Examples of the use of thick (up to 5 mm) stainless steel or bronze coatings as claddings on steel, aluminum or zirconium rods in order to provide good ultrasonic wave guides are given. Compared to a conventional non-clad rod the signal to noise ratio of such clad rods has been improved by more than 40 dB due to the reduction of the spurious signals. The potential applications of these clad buffer rods for thickness measurements and in-situ monitoring of materials at elevated temperatures are demonstrated.

One cause of aseptic loosening of total hip replacement (THR) results from the hard polymetylmethacrylate (PMMA) bone cement debris embedded within some of acetabular cups [1]. To prevent this failure, PMMA can be replaced by a titanium coating with a specific roughness to promote the bone bonding. In this work, inert and atmospheric plasma spraying was used to coat Ti.6A1.4V implants with titanium.] In order to evaluate the effect of the deposition process on the coating corrosion resistance, different electrochemical techniques were implemented in physiological (i. e., Ringer) and in acidic solutions. Results show that the spraying parameters and the coating morphology affect the corrosion behaviour. Thus, if the reactivity is not affected by the pH evolution, the pitting sensitivity depends on the process. It was found that coatings deposited under inert gas are free of oxides and dense, even when the atmosphere contains some hydrogen. In that case a significant improvement of the intrinsic localized corrosion resistance is observed versus deposits obtained using atmospheric plasma spraying.