Several novel cored wires for producing Fe 3 Al intermetallic coating, Fe 3 Al/WC intermetallic coating, FeCrAl/WC intermetallic coating and FeCrNi/WC intermetallic coating by arc spraying were developed. The erosion wastage at high temperature of coatings was researched with different impingement angles and temperatures. The results indicated that impingement angle and temperature greatly affected FeCrAl/WC coating and Fe 3 Al/WC coating in erosion wastage. At the same time, the FeCrAl/WC coating had little effects on different temperature while impingement angle was 90° and different impingement angle while temperature was 650°C. As compared with water wall tube material (G20 steel) of power station boiler, the erosion resistance at high temperature of Fe 3 Al coating, Fe 3 Al/WC coating and FeCrAl/WC coating was higher. The erosion resistance rate of Fe 3 Al coating was 1.4~2.91 times of that of G20 steel when temperature was 650°C and particle was polygonal silica. At the same time, the erosion resistance rates of Fe 3 Al/WC coating and FeCrAl/WC coating was 1.4~3.06 and 1.94~2.89 times respectively. The results indicated that erosive condition of high temperature flue gas and fly ash mixture in boiler tube of pulverized coal fired power station could be solved with Fe 3 Al coating, Fe 3 Al/WC coating and FeCrAl/WC coating.

Erosion-corrosion is a severe problem observed in the coal fired thermal power plant boilers which lead to premature failure of boiler tubes. Thermal spray coatings have been applied successfully to check the erosion-corrosion of boiler tubes. In the present research work NiCrTiCRe coating powders were successfully deposited on T22 boiler steel by two different coating processes i.e. high velocity oxy-fuel (HVOF) and cold spray process. The performance of the coatings in actual power plant boiler were investigated and compared. The uncoated and coated T22 boiler steels were subjected the superheater zone of the coal fired boiler for a total of 15 consequent cycles. The thickness loss data and weight change analysis were used to establish kinetics of the erosion-corrosion. X-ray diffraction, surface field emission scanning electron microscope/energy dispersive spectroscopy (FE-SEM/EDS) techniques were used in the present work for the analysis. The results of thickness loss data indicated that the cold sprayed coating performed better in thermal power plant boiler environment.

The elevated temperature erosion resistance of experimental amorphous thermal spray coatings was determined in a laboratory elevated temperature erosion tester. Test conditions attempted to simulate the erosion conditions found at the combustor waterwall tubes in fossil fuel fired boilers. Erosion tests were conducted on four experimental amorphous thermal spray coatings, using the bed ash retrieved from an operating coal fired boiler. An experimental arcspray process was used to spray coatings. These results were compared with erosion test results of two common structural materials, two commercially available arc-sprayed coatings, and a proprietary HVOF coating. Test results indicated that the Duocor coating had the highest erosion resistance among the four experimental coatings, it showed equal resistance to the HVOF coating (DS-200). Compared to AISI 1018 steel, both Duocor and DS-200 coatings reduced material wastage by 26-fold. Other test results indicated that the XJ-16, 60T and Armacor M coatings had equal erosion resistance reducing material wastage approximately 7-fold, while Armacor CW reduced by 10-fold. Only slightly better than the unprotected 1018 steel, the X-20 coating performed poorly on erosion tests. The high erosion resistance of Duocor and DS-200 coatings was attributed to their high densities and fine splat structures.

This study evaluates Fe-Si intermetallic powders as an alternative to powders currently used to coat furnace walls in pulverized coal fired boilers. The developed powder mainly consists of Fe 2 Si, which has a relatively low melting point among iron silicides. The powders were deposited on CrMo steel substrates by HVOF and atmospheric plasma spraying and the resulting coatings were subjected to corrosion and erosion testing. Under conditions simulating the operating environment in a low NO X boiler, the HVOF sprayed Fe-Si coatings exhibited sulfidation resistance nearly equal to that of Cr-Ni layers, and in high-temperature erosion tests, the APS intermetallic coatings with boron additions were found to be more erosion resistant than conventional Cr 3 C 2 -NiCr coatings.

This study assesses the fireside erosion-corrosion behavior of nanostructured NiCr coatings in a power plant boiler operating at 750 °C. In the experiments, Ni-20Cr nanocrystalline powder was synthesized by ball milling and deposited on T91 boiler steel substrates by HVOF spraying. Coated and uncoated steel specimens were thermally cycled in the superheater zone of a coal fired boiler. After 15 heating and cooling cycles, the specimens were examined and erosion-corrosion kinetics were established via weight-change and thickness-loss measurements. The results show that the nanostructured coatings reduced the erosion-corrosion rate of T91 steel by 85%.

In the present work, commercially available NiCr and NiCr-TiC powder blends were deposited on boiler steel substrates by HVOF spraying. To evaluate coating performance, bare and coated steel samples were placed in the superheater zone of a coal fired boiler for 15 cycles. Weight change and thickness loss were measured and the results were used to establish erosion-corrosion kinetics. XRD and SEM/EDS techniques were used to analyze the microstructure and phase composition of as-sprayed and eroded-corroded specimens. The improvement in erosion-corrosion resistance provided by the coating may be attributed to the formation of nickel and chromium oxides and spinels.

This study examines the high-temperature erosion characteristics of carbide cermet coatings produced by HVOF spraying. The coating materials tested include three Cr 3 C 2 cermets, WC, and WC-Cr 3 C 2 . A low carbon steel and an arc-sprayed iron-base coating are also tested for reference. A nozzle-type elevated-temperature erosion tester is used to spray bed ashes collected from several coal-fired boilers. Coating samples are analyzed and compared based on composition, surface morphology, erosion wastage, and hardness relative to that of the bed-ash particles. From the comparisons, a number of conclusions are drawn. Paper includes a German-language abstract.

New composite materials thermally spray powder is developed in order to protect the surface of boiler tube while long period more than up to this time. This powder is so constitute that original sermet is organized from several bolides and inter metallic compounds (patent pending applied for). For the reliable electric power supply, the steam generating boiler is important facility still today. And in boiler operation, one of the most significant problems is the prevention of boiler tube failure. The main destructive processes that ravage boiler tubes are corrosion and erosion. During the last several years, thermally sprayed coating has been applied to the surfaces of boiler tubes. Accordingly, this paper reports on the effects of this developed powder’s coating as compared with these conventional coatings on the prevention of these hot abrasion are tested in laboratory.

The significant erosion of the boiler tube at high temperature becomes an important problem for the safe operation of circulating fluidized bed boiler. This paper investigated the erosion behavior of the HVOF sprayed Cr 3 C 2 -NiCr coating at high temperature comparing with the typical mild steel for boiler tube. Results showed that the erosion rate of the mild steel increased with the increase of temperature. The erosion rate of the mild steel at 800°C was 4 times that at 300°C at an erosion angle of 30°. However, the erosion rate of the HVOF sprayed Cr 3 C 2 -NiCr coating was not influenced by the temperature in the range of 300 to 800°C. It is found that the erosion resistance of HVOF sprayed Cr 3 C 2 -NiCr coating was more than 3 time higher than that of the mild steel at 700 to 800°C. In addition to the ploughing on the surface of the worn coating, the cracking along splats interfaces in the coating was clearly observed on the cross-sectional microstructure of the coating. The results indicate that the erosion performance of the HVOF sprayed Cr 3 C 2 -NiCr coating is controlled by the cohesion between splats in the coating and can be further enhanced by improving splat cohesion.

A study was carried out to determine the role of HVOF-spray Ni-20Cr coatings to enhance high temperature oxidation resistance of T22 and 347H boiler steels. Ni-20Cr coatings were deposited on the boiler steels. Subsequently high temperature oxidation behavior of these coatings was investigated by laboratory tests at an elevated temperature of 9000C under cyclic conditions. These coatings were also subjected to a boiler environment at an elevated temperature of 700ºC under cyclic conditions to ascertain their erosion-corrosion behaviour. Thermogravimetric data was taken after each cycle to formulate the oxidation, as well as, erosion-corrosion kinetics. The specimens were also physically examined after each cycle to notice any macrographic physical changes, spallation tendency of their oxide scales etc. The exposed specimens were examined using scanning electron microscopy and Energy Dispersive Spectroscopy (SEM/EDS) analysis. It was observed that oxidation rate was subsequently low in the coated substrates as compare to uncoated steels. It was observed that Ni-20Cr coating on 347H boiler substrate showed the maximum oxidation resistance. Moreover, both the steels showed better resistance to erosion-corrosion in actual boiler conditions after the application of Ni-20Cr coating.

In the current work, Ni-20Cr coatings have been developed for potential use in harsh environments of power plant boilers. A pre-synthesized Ni-20Cr nanocrystalline powder was deposited on T22 boiler steel using cold-spray process. The high temperature oxidation behavior of the coating was investigated under cyclic conditions at 900° C for 50 cycles, so as to understand the kinetics of oxidation. Moreover, high temperature erosion-corrosion (E-C) behaviour of the coating was ascertained under cyclic conditions in an actual boiler at 740 ± 10°C for 1500 hours. The oxidized and eroded-corroded samples were characterized using X-ray Diffraction (XRD), Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS) analyses. The microhardness, oxidation and E-C data for the developed coating was compared with an earlier reported cold-spray Ni-20Cr coating, which was developed by using a commercially available micron-sized Ni-20Cr powder. The results showed that the developed coating was found to have 33% high microhardness in comparison with the microstructured Ni-20Cr coating. The oxidation and E-C rates of the steel were found to decrease significantly after the application of the developed coating by 89% and 68% respectively. Moreover the nanostructured coating outperformed the corresponding micro-structured Ni- 20Cr coating with regard to high temperature oxidation and E-C resistance to boiler steel by a significant fraction. The investigated coating was found to have oxidation protective oxides such as Cr 2 O 3 and NiO in its oxide scale and was found to be spallation-free.

In biomass boilers, corrosion is a prevalent concern that arises at high temperatures. This is mainly because the fuels consumed in these boilers have a high alkali, chlorine, and other molten salt content that has occasionally led to material depletion, leaks, and unforeseen plant shutdowns. Applying protective coatings using thermal spray techniques is a practical answer to this issue. The current work focused on applying powders of Inconel 625 and Inconel 718 to boiler steel using a high-velocity oxy-fuel spraying method. The samples after coating deposition were subjected to the conditions of a biomass-fired boiler for 15 cycles to study the performance of the coatings in a real environment. The decrease of thickness over time was used to evaluate the erosion-corrosion process. Various characterization techniques were used to examine the as-sprayed and eroded-corroded specimens. The X-ray diffraction (XRD) technique was utilized to analyze the phases, while the surface characteristics of powders, coatings, and samples exposed to erosion-corrosion were investigated through scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDS). When exposed to the actual boiler environment, the findings showed that Inconel 625-coated steel performed better than Inconel 718-coated steel.

High velocity oxygen-fuel (HVOF) thermal spray processes are used in applications requiring the highest density and adhesion strength, which is not achievable in most other thermal spray processes. Like other thermal spray processes, however, a normal HVOF process is not able to apply fine powders less than 10 µm via a conventional powder feeder. The advantages of using smaller and even nano-sized particles in a HVOF process include uniform coating, less defective microstructure, higher cohesion and adhesion, full density, lower internal stress and higher deposition efficiency. A new process has been developed to realize HVOF forming of fine-grained alloy layers by using liquid precursors containing fine metallic particles. Process investigations have shown the benefits for making single and duplex layered coatings with full density and high bond strength attributing to the very high kinetic energy of particles striking on the substrate surface and the better melting of the small particles. One of the targeted applications is for the water walls of a fossil-fired boiler that operate in a high temperature and corrosive environment. The new coating system is based on material selection, structure design, process innovation and diagnostics, microstructure, and property evaluation. It is promising to provide better protection of the boilers against various types of degradations like corrosion, oxidation, erosion and interfacial failure.

Boiler tube failure is the number one source of forced outages in all coal-fired and biomass-fired power generation plants. It is estimated that plants lose approximately 6% of their power generation annually, due to boiler tube leaks. The major causes for premature tube failure are excessive fireside boiler tube erosion and corrosion caused by impact, abrasive wear, oxidation and molten corrosion of low eutectic alloys.

In this investigation, a nanostructured NiCr coating was deposited on boiler steel by cold spraying and its oxidation behavior was evaluated under cyclic thermal conditions. Oxidation kinetics were established through weight change measurements and the oxidized samples were characterized using XRD and SEM analysis and X-ray mapping. The nanostructured coating was more than two times harder than its microstructured equivalent and in oxidation tests, reduced the weight gain of the boiler steel by 68%. The coating was found to have protective oxides in its oxide scale and was shown to be spallation-free.

In this study, several thermal spray coatings and reference materials were evaluated for potential use in biomass co-fired boilers. The coatings were applied to T92, A263, and X10Cr13 substrates by HVOF and wire-arc spraying using powder (IN625, FeCr, NiCr) and wire (NiCrTi) feedstocks. Coating samples were examined then tested for 5900 h in the superheater area of a fluidized bed boiler burning a mixture of wood, peat, and coal. The corrosion behavior of the coating and reference materials is reported in the paper and the underlying corrosion mechanisms are discussed.

The goal of this work is to develop a flame sprayed NiCr-Cr 3 C 2 coating that resists oxidation, corrosion, and erosion in boiler environments and to assess the influence of Cr 3 C 2 fraction and sealing on coating performance. In the experiments, NiCr cermet alloys with different proportions of chromium carbide were applied to boiler steel substrates by means of subsonic velocity flame spraying and some of the coatings were sealed with a silicon resin. The paper describes the various tests performed and presents the results. Paper includes a German-language abstract.

This paper provides a general overview of arc spraying and its various uses in industry. It discusses the basics of the technique, the types of wires and powders used, and typical applications for a wide range of arc-sprayed metals and composites. It also discusses special cases and considerations such as wear protection in corrosive atmospheres, high-temperature corrosion protection, surface rebuilding and reprofiling, coating thickness, and the effect of different elements. Paper includes a German-language abstract.

This study compares the corrosion resistance of a wide range of coatings in a chlorine-containing atmosphere at elevated temperatures. Four HVOF-sprayed NiCr coating samples were produced and tested along with an iron-aluminide HVOF layer, a chromium diffusion layer, and a laser-treated HVOF NiCrMo layer. The investigators found that the structure of HVOF coatings has a major effect on corrosion resistance and that chlorine corrosion primarily attacks the substrate through cracks and interconnected networks of pores and oxides at splat boundaries. They also observed that laser melting increases corrosion resistance by homogenizing the coating structure. Paper includes a German-language abstract.

In this study, FeCr coatings with different percentages of chromium were deposited on Grade 91 steel substrates by HVOF spraying, followed by aluminum enrichment via pack cementation. Overaluminizing parameters were optimized to prevent changes in the substrate microstructure, making it possible to determine the role of Cr and the effect of Al enrichment on anticorrosion behavior. The combination of HVOF spraying and pack cementation are shown to be adequate techniques for depositing intermediate and top layers in protective coating systems.