Combating Corrosion Degradation of Turbine Materials Using HVOF Sprayed 25% (Cr3C2-25(Ni20Cr)) + NiCrAlY Coating (original) (raw)
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Metallurgical and Materials Transactions A, 2010
The high-velocity oxy-fuel (HVOF) spray technique was used to deposit Ni-20Cr coating on a commonly used boiler steel ASTM A213 347H. The specimens with and without coating were exposed to the super heater zone of a thermal power plant boiler at a temperature of 973 K (700°C) under cyclic conditions to ascertain their erosion-corrosion (E-C) behavior. High-temperature oxidation behavior of the specimens was also evaluated under cyclic thermal loading conditions at an elevated temperature of 1173 K (900°C). Mass change data and thickness loss were measured to formulate the kinetics of E-C/oxidation for the specimens. The exposed specimens were characterized by X-ray diffraction (XRD) and field emission-scanning electron microscopy/energy dispersive spectroscopy (FE-SEM/EDS). The uncoated steel suffered higher E-C in comparison with its coated counterpart in terms of mass loss as well as thickness loss. It was observed that overall mass loss was reduced by 31 pct and thickness loss by 44 pct after the application of the coating. The possible formation of Cr 2 O 3 phase in the coated substrate may be suggested to contribute to better E-C behavior. During air oxidation exposures, the coating was found to be intact with only marginal spallation of its oxide scales, which is an indicator of good adhesion between the coating and substrate steel. The air oxidation mass change data indicated that the coating enhanced the oxidation resistance of the steel by 85 pct.
Hot Corrosion Behaviour of HVOF Sprayed Stellite-6 Coatings on Gas Turbine Alloys
The coal burned natural gas in contact with gas turbine can contain impurities of sodium, sulfur, vanadium, silicon and possibly lead and phosphorous, induce accelerated hot corrosion during long term operation. Coatings are frequently applied on gas turbine components in order to restrict surface degradation and to obtain accurate lifetime expectancies. High velocity oxy-fuel thermal spraying has been used to deposit Stellite-6 alloy coatings on turbine alloys. Hot corrosion behavior of the coatings were investigated for 50 cycles of 1 h heating at 800°C followed by 20 min cooling in presence of Na 2 SO 4 ? 50 % V 2 O 5 measuring weight gain (or loss). X-ray diffraction and SEM/ EDAX techniques were used to characterize the oxide scale formed. The superior performance of Stellite-6 coating can be attributed to continuous and protective thin oxide scale of CoO, Cr 2 O 3 and SiO 2 formed on the surface. The coating region beneath this thin oxide scale was partially oxidized. Uncoated SuperCo-605 and MDN-121 showed less weight gain than Stellite-6 coated samples, but they showed spalling or sputtering during cyclic oxidation. Stellite-6 coating was dense and pore free even after 50 cycles, indicating that it can resist the hot corrosion cycle.
Laboratory and field corrosion behavior of coatings for turbine blades
Surface and Coatings Technology, 1997
The present work reports the results of a comparative evaluation of three commercial coatings for turbine blades: (i) low activity pack cementation aluminide; (ii) high activity pack cementation Pt modified aluminide: and (iiij slurry deposited Si modified aluminide. For a laboratory corrosion test, bare substrate (Udimet 520) and coated samples were subjected to two different salts baths, 25% NaCl-75% Na$04 and 100% NalSOA, at 750°C in an inert atmosphere (Ar) and a gas mixture of S03-SO&. For a rainbow teht, nine coated blades were mounted in a gas turbine for 10 000 h. The test results showed that for the N&l-Na2S0, bath the damage mode of bare samples was Type I hot corrosion, while for the 100% Na2S04 bath thedamage was Type II; this effect was independent of the tebt atmosphere. Coated samples showed an incipient corrosion for the same test,. In accordance with the damage intensity, the coatings were rated (from Worst to best) as: Al-Pt, Al, Al-Si. The rainbow test showed the same tendency; however, the corrosion damage was less intensive in all cases. 0 1997 Elsevier Science S.A.
High-Temperature Behavior of a High-Velocity Oxy-Fuel Sprayed Cr3C2-NiCr Coating
Metallurgical and Materials Transactions A, 2012
High-velocity oxy-fuel (HVOF) sprayed coatings have the potential to enhance the high-temperature oxidation, corrosion, and erosion-corrosion resistance of boiler steels. In the current work, 75 pct chromium carbide-25 pct (nickel-20 pct chromium) [Cr 3 C 2 -NiCr] coating was deposited on ASTM SA213-T22 boiler steel using the HVOF thermal spray process. Hightemperature oxidation, hot corrosion, and erosion-corrosion behavior of the coated and bare steel was evaluated in the air, molten salt [Na 2 SO 4 -82 pct Fe 2 (SO 4 ) 3 ], and actual boiler environments under cyclic conditions. Weight-change measurements were taken at the end of each cycle. Efforts were made to formulate the kinetics of the oxidation, corrosion, and erosioncorrosion. X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM)/energy dispersive spectroscopy (EDS) techniques were used to analyze the oxidation products. The coating was found to be intact and spallation free in all the environments of the study in general, whereas the bare steel suffered extensive spallation and a relatively higher rate of degradation. The coating was found to be useful to enhance the high-temperature resistance of the steel in all the three environments in this study.
Development and Assessment of Coatings for Future Power Generation Turbines
Volume 5: Manufacturing Materials and Metallurgy; Marine; Microturbines and Small Turbomachinery; Supercritical CO2 Power Cycles, 2012
The NETL-Regional University Alliance (RUA) continues to advance technology development critical to turbine manufacturer efforts for achieving DOE Fossil Energy (FE's) Advanced Turbine Program Goals. In conjunction with NETL, Coatings for Industry (CFI), the University of Pittsburgh, NASA GRC, and Corrosion Control Inc., efforts have been focused on development of composite thermal barrier coating (TBC) architectures that consist of an extreme temperature coating, a commercially applied 7-8 YSZ TBC, a reduced cost bond coat, and a diffusion barrier coating that are applied to nickel-based superalloys or single crystal airfoil substrate materials for use at temperatures >1450ºC (> 2640ºF). Additionally, construction of a unique, high temperature (~1100ºC; ~2010ºF), bench-scale, micro-indentation, nondestructive (NDE) test facility at West Virginia University (WVU) was completed to experimentally address in-situ changes in TBC stiffness during extended cyclic oxidation exposure of coated single crystal coupons in air or steamcontaining environments. The efforts and technical accomplishments in these areas are presented in the following sections of this paper.
Journal of Materials Processing Technology, 2004
Hard chromium plating is usually used to restore to original dimensions the worn surfaces of gas turbine shafts. However, such a technology presents harmful effects on the environment and the public health and it exhibits, moreover some intrinsic technical limitations. HVOF (high-velocity oxy-fuel) thermal spraying process appears as more environmentally friendly than chromium plating process but exhibits also lower potential production costs when compared to hard chromium deposits.
METAL 2021 Conference Proeedings, 2021
The paper focuses on the evaluation of the ability of selected heat sprayed coatings to protect the surface of the component in an environment simulating the environment of a geothermal turbine. The subject of testing were coatings based on hardmetals, applied by HVOF technology (WC-CoCr, Cr3C2-NiCr) and Fe and Ni based alloys, applied by HVOF (NiCr, FeCrAlY) and TWAS (FeCrAlNiC, FeCr, NiCr) technologies. It has been shown that although HVOF coatings provide higher protective properties in terms of both corrosion and resistance to mechanical influences, it is also possible to apply the protective coating with TWAS technology if mobile spraying is required. From the materials tested, the Fe-based Metco 8294 can be recommended as a most promising, providing high wear resistance and sufficient corrosion resistance in aggressive environment.
Oxidation Resistance HVOF Sprayed Coating 25% (Cr3C2- 25(Ni20Cr)) + 75%NiCrAlY on Titanium Alloy
Procedia Materials Science, 2014
The titanium alloys posses good affinity towards oxygen at elevated temperature in air and thereby leading to oxidation. The current paper presents the oxidation behaviour of titanium alloy, Ti-6Al-4V at elevated temperature. The degradation of the alloy oxidation mechanism is described in detail. Rapid degradation or the inability to repair these complex material results in excessively high operating costs. A suitable protective HVOF coating 25% (Cr 3 C 2-25(Ni20Cr)) + 75% NiCrAlY was sprayed on Ti-31 alloy to combat oxidation to improve the life and efficiency of components. Thermogravimetric technique was used to study the high temperature oxidation behaviour of bare and coated alloy at 800ºC for 50 cycles, 1 hr heating in tube furnace and 20 minutes colloing in atmospheric temperature. The oxidized products are analyzed using XRD and SEM/EDX. It is observed that a coating has less porosity and semi melted powder particles in the structure. Also the coating has imparted necessary oxidation resistance by formation of chromium and nickels oxides.
Corrosion and Wear Studies of Cr3C2NiCr-HVOF Coatings Sprayed on AA7050 T7 Under Cooling
Journal of Thermal Spray Technology, 2009
In this work, cermet coatings were prepared by high-velocity oxygen-fuel (HVOF) technique using a Diamalloy 3007 powder. The influence of the spray parameters on corrosion, friction, and abrasive wear resistance was studied. The samples were obtained using the standard conditions (253 L/min of oxygen and 375 L/min of compressed air), higher oxygen flux (341 L/min), and higher carrier gas flux (500 L/min). The coatings were characterized using scanning electron microscopy (SEM), and x-ray diffraction (XRD). X-ray diffraction and SEM studies showed well-bounded coating/substrate interface, pores, metallic matrix, chromium oxides, carbides, and carbides dissolution into the matrix. In comparison with the standard condition, the sample prepared using higher oxygen flux showed the highest carbide dissolution because of the high temperature achieved in the spray process. When the carrier gas flux was increased, the sample showed denser structure because of the higher particle velocity. The friction and abrasive wear resistance of the coatings were studied using rubber wheel and ball-on-disk tests. All samples showed similar sliding and abrasive behavior, and all of them showed better performance than the aluminum alloy. The electrochemical behavior was evaluated using open-circuit potential (E OC ) measurements, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization curves. The coating prepared with higher carrier gas flux showed the highest corrosion resistance in 3.5% NaCl solution and probably no pitting attack to the substrate occurred even after around 26 h of test. Tests performed for longer immersion times showed that the total impedance values significantly decreased (6 and 4 times) for samples sprayed using standard and higher oxygen flux, and no great change for sample sprayed using higher carrier gas flux was observed. The last sample presents a corrosion resistance around 200 times higher than the others.