Resistance of Thermally Sprayed Coatings in an Environment Simulating a Turbine of Geotermal Power Plant (original) (raw)
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International Journal of Corrosion, 2013
High velocity oxy fuel process (HVOF) is an advanced coating process for thermal spraying of coatings on to components used in turbines. HVOF process is a thermal spray coating method and is widely used to apply wear, erosion, and corrosion protective coatings to the components used in industrial turbines. 25% (Cr 3 C 2-25(Ni20Cr)) + NiCrAlY based coatings have been sprayed on to three turbine materials, namely, Ti-31, Superco-605, and MDN-121. Coated and uncoated substrates were subjected to hot corrosion study under cyclic conditions. Each cycle consisted of 1 hour heating at 800 ∘ C followed by 20 minutes air cooling. Gravimetric measurements were done after each cycle and a plot of weight gain as a function of number of cycles is drawn. Parabolic rate constants were estimated for the understanding of corrosion behaviour. It was observed that coated Ti-31 and MDN-121 were more resistant compared to the uncoated ones. Uncoated superco-605 was undergoing sputtering during corrosion study and hence comparison between coated and uncoated superco-605 was difficult. The cross-sectional analysis of the corroded, coated samples indicated the presence of a thin layer of chromium oxide scale on the top of the coating and it imparted better corrosion resistance. Parabolic rate constants also indicated that coating is more beneficial to Ti-31 than to MDN-121.
Journal of Thermal Spray Technology, 2019
High-temperature corrosion of critical components such as water walls and superheater tubes in biomass/ waste-fired boilers is a major challenge. A dense and defect-free thermal spray coating has been shown to be promising to achieve a high electrical/thermal efficiency in power plants. The field of thermal spraying and quality of coatings have been progressively evolving; therefore, a critical assessment of our understanding of the efficacy of coatings in increasingly aggressive operating environments of the power plants can be highly educative. The effects of composition and microstructure on high-temperature corrosion behavior of the coatings were discussed in the first part of the review. The present paper that is the second part of the review covers the emerging research field of performance assessment of thermal spray coatings in harsh corrosion-prone environments and provides a comprehensive overview of the underlying high-temperature corrosion mechanisms that lead to the damage of exposed coatings. The application of contemporary analytical methods for better understanding of the behavior of corrosion-resistant coatings is also discussed. A discussion based on an exhaustive review of the literature provides an unbiased commentary on the advanced accomplishments and some outstanding issues in the field that warrant further research. An assessment of the current status of the field, the gaps in the scientific understanding, and the research needs for the expansion of thermal spray coatings for high-temperature corrosion applications is also provided.
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 Thermal Spray Technology, 2019
Power generation from renewable resources has attracted increasing attention in recent years owing to the global implementation of clean energy policies. However, such power plants suffer from severe high-temperature corrosion of critical components such as water walls and superheater tubes. The corrosion is mainly triggered by aggressive gases like HCl, H 2 O, etc., often in combination with alkali and metal chlorides that are produced during fuel combustion. Employment of a dense defect-free adherent coating through thermal spray techniques is a promising approach to improving the performances of components as well as their lifetimes and, thus, significantly increasing the thermal/electrical efficiency of power plants. Notwithstanding the already widespread deployment of thermal spray coatings, a few intrinsic limitations, including the presence of pores and relatively weak intersplat bonding that lead to increased corrosion susceptibility, have restricted the benefits that can be derived from these coatings. Nonetheless, the field of thermal spraying has been continuously evolving, and concomitant advances have led to progressive improvements in coating quality; hence, a periodic critical assessment of our understanding of the efficacy of coatings in mitigating corrosion damage can be highly educative. The present paper seeks to comprehensively document the current state of the art, elaborating on the recent progress in thermal spray coatings for high-temperature corrosion applications, including the alloying effects, and the role of microstructural characteristics for understanding the behavior of corrosion-resistant coatings. In particular, this review comprises a substantive discussion on high-temperature corrosion mechanisms, novel coating compositions, and a succinct comparison of the corrosion-resistant coatings produced by diverse thermal spray techniques.
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.
Thermo-Mechanical Characterizations of Coatings for HP Turbines
Volume 5: Manufacturing Materials and Metallurgy; Ceramics; Structures and Dynamics; Controls, Diagnostics and Instrumentation; Education, 1998
Three different coatings were studied in this work : vacuum plasma-sprayed NiCoCrAlYTa, electrolytically deposited NiCoCrAlYTa and Ni-Pt aluminide diffusion coatings. These three coatings were deposited on AM3 single crystal alloy, lit tensile properties of coated single crystal test specimens wae investigated. Ductile to Brittle Transition Temperatures (DM) were determined from tensile tests. All the coatings wae examined before and after testing. All the tested coatings induce a ductile/brittle transition. Strain rate has a great influence on the transition temperature. The comparison between plasma-sprayed deposition aid electrodeposition illustrates the strong influence of coating microstructure. In every case, NiCoCrAlYTa coatings were more ductile, and then less detrimental, than aluminide coatings.
Applied Sciences
The aim of this paper is to establish the cost-effectiveness of high-entropy alloy coatings, using the electrospark deposition technique, designed for a geothermal turbine blade’s leading edge. The deposition of materials with high resistance to corrosion and erosion aims to increase the blade’s service life, reduce maintenance costs and improve production efficiency. According to our previous research on the CoCrFeNiMox high-entropy alloy system, the results showed a high corrosion resistance when in bulk or as a coating, and when tested in geothermal steam and in a saline solution. Based on the results, the high-entropy alloy was subjected to further analyses. The paper focused on two aspects of the research. The first direction was to explore the possibility of obtaining an effective, protective high-entropy alloy layer by the electrospark deposition method. To this end, various tests were performed to demonstrate that the new material possesses superior properties and is suitabl...
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.
Gas turbine coatings – An overview
The components of a gas turbine operate in an aggressive environment where the temperature of service varies from ambient to near melting point of materials which introduce a variety of degradation on the components. Some components that lose their dimensional tolerance during use require repair and refurbishment when high cost replacement is avoidable. Erosion of fly ash and sand particles damages compressor blades which cause engine failure at an early stage. Dovetail roots of the compressor blades are subjected to fretting fatigue due to the oscillatory motion caused by vibration. Casing of the compressor comes in contact with rotating blades due to shaft misalignment, ovality of the casing and or inadequate clearance which cause blade and casing damage. Close clearance control that has bearing on the efficiency of the engine is therefore required in addition to preventing fire where titanium to titanium rubbing might occur. Wear out of the several contact surfaces which undergo rotating and reciprocating motion occur during the running of the engine need protection. Hot gases that are produced by burning the contaminated fuel in the combustion chamber will cause oxidation and corrosion on their passage. In the hot section rotating and stationary components need thermal insulation from higher operating temperature leading to enhanced thermodynamic efficiency of the engine. This wide range of functional requirements of the engine is met by applying an array of coatings that protect the components from failures. Current overview, while not aiming at deeper insight into the field of gas turbine coatings, brings out a summary of details of these coatings at one place, methods of application and characterization, degradation mechanisms and indicative future directions which are of use to a practicing industrial engineer.