Search Results for coatings

The EU NextGenPower-project aims at demonstrating Ni-alloys and coatings for application in high-efficiency power plants. Fireside corrosion lab and plants trials show that A263 and A617 perform similar while A740H outperforms them. Lab tests showed promising results for NiCr, Diamalloy3006 and SHS9172 coatings. Probe trials in six plants are ongoing. A617, A740H and A263 performed equally in steamside oxidation lab test ≤750°C while A617 and A740H outperformed A263 at 800°C; high pressure tests are planned. Slow strain rate testing confirmed relaxation cracking of A263. A creep-fatigue interaction test program for A263 includes LCF tests. Negative creep of A263 is researched with gleeble tests. A263 Ø80 - 500mm trial rotors are forged with optimized composition. Studies for designing and optimizing the forging process were done. Segregation free Ø300 and 1,000mm rotors have been forged. A263 – A263 and A293 – COST F rotor welding show promising results (A263 in precipitation hardened condition). Cast step blocks of A282, A263 and A740H showed volumetric cracking after heat treatment. New ‘as cast’ blocks of optimized composition are without cracks. A 750°C steam cycle has been designed with integrated CO 2 capture at 45% efficiency (LHV). Superheater life at ≤750°C and co-firing is modeled.

Solid particle erosion (SPE) harms steam and gas turbines, reducing efficiency and raising costs. The push for ultra-supercritical turbines reignited interest in SPE’s impact on high-temperature alloys. While the gas turbine industry researches methods to improve erosion resistance, a similar need exists for steam turbines. Existing room-temperature SPE test standards are insufficient for evaluating turbine materials. To address this gap, an EPRI program is developing an elevated-temperature SPE standard. This collaborative effort, involving researchers from multiple countries, has yielded a draft standard submitted to ASTM for approval. This presentation will detail the program, test conditions, and the draft standard’s development.

Over the past two decades there has been considerable interest in the development of coatings with finer microstructures approaching nanometer scale because these coatings are more resistant to high-temperature oxidation and corrosion than their counterpart conventional coatings. Long-term cyclic oxidation behavior of nanocrystalline FeCrNiAl and NiCrAl coatings were evaluated at different temperatures and the results showed that ultra-fine grain structure promoted selective oxidation of Al during thermal exposure. The protective Al2O3 scale formed on these coatings with Al content as low as 3 wt.% and exhibited excellent spallation resistance during thermal cycling. The nanocrystalline NiCrAl coating showed significantly higher oxidation resistance compared to the conventional plasma sprayed NiCoCrAlY and PWA 286 coatings. However, the Al content in the nanocrystalline coatings was consumed in relatively short time due to inward and outward diffusion of Al. Variation of oxide-scale spallation resistance during thermal cycling and the rate of Al consumption between the nanocrystalline and plasma sprayed coatings are compared.

Abradability, erosion and steam oxidation tests were conducted on commercial and experimental abradable coatings in order to evaluate their suitability for applications in steam turbines. Steam oxidation tests were carried out on free-standing top coat samples as well as coating systems consisting of a bond and an abradable top coat. Mapping of the abradability performance under widely varied seal strip incursion conditions was carried out for a candidate abradable coating that showed good steam oxidation performance in combination with good erosion resistance. The abradability tests were carried out on a specially designed test rig at elevated temperatures. The steam oxidation analysis combined with the abradability mapping results provide a potentially improved seal coating system that can be integrated into existing steam turbine designs for various seal locations. Such design integration is easily achieved and can be applied to steam turbine components that are sprayed in dedicated coating shops or even at the site of final turbine assembly.

Diffusion aluminide coatings have been evaluated as a strategy for improving the oxidation resistance of austenitic and ferritic-martensitic (FM) steels, particularly in the presence of steam or water vapor. The objective was to evaluate the strengths and weaknesses of these coatings and quantify their performance and lifetime. Long-term diffusion and oxidation experiments were conducted to study the behavior of various model diffusion coatings and produce a better data set for lifetime predictions. The key findings are that (1) thin coatings (<50μm) with relatively low Al contents appear to be more effective because they avoid high thermal expansion intermetallic phases and have less strain energy to nucleate a crack; and (2) the low Al reservoir in a thin coating and the loss of Al due to interdiffusion are not problematic because the low service temperatures of FM steels (<600°C) and, for austenitic steels at higher temperatures, the phase boundary between the ferritic coating-austenitic substrate inhibits Al interdiffusion. Unresolved issues center on the effect of the coating on the mechanical properties of the substrate including the reaction of N in the alloy with Al.

Solid particle erosion (SPE) and liquid droplet erosion (LDE) cause severe damage to turbine components and lead to premature failures, business loss and rapier costs to power plant owners and operators. Under a program funded by the Electric Power Research Institute (EPRI), nano­coatings are under development for application in steam and gas turbines to mitigate the adverse effects of PE and LPE on rotating blades and stationary vanes. Based on a thorough study of the available information, most promising coatings such as nano-structured titanium silicon carbo-nitride (TiSiCN), titanium nitride (TiN) and multilayered nano coatings were selected. TurboMet International (TurboMet) teamed with Southwest Research Institute (SwRI) with state-of-the-art nano-technology coating facilities with plasma enhanced magnetron sputtering (PEMS) method to apply these coatings on various substrates. Ti-6V-4Al, 12Cr, 17-4PH, and Custom 450 stainless steel substrates were selected based on the current alloys used in gas turbine compressors and steam turbine blades and vanes. Coatings with up to 30 micron thickness have been deposited on small test coupons. These are extremely hard coatings with good adhesion strength and optimum toughness. Tests conducted on coated coupons by solid particle erosion (SPE) and liquid droplet erosion (LDE) testing indicate that these coatings have excellent erosion resistance. The erosion resistance under both SPE and LDE test conditions showed the nano-structured coatings have high erosion resistance compared to other commercially produced erosion resistance coatings. Tension and high-cycle fatigue test results revealed that the hard nano-coatings do not have any adverse effects on these properties but may provide positive contribution.

Erosion from solid and liquid particles in gas turbine and steam turbine compressors degrades efficiency, increasing downtime and operating costs. Conventional erosion-resistant coatings have temperature and durability limitations. Under an Electric Power Research Institute (EPRI) project, ultra-hard nano-coatings (~40 microns thick) were developed using Plasma Enhanced Magnetron Sputtering (PEMS). In Phase I, various coatings—including TiSiCN nanocomposites, stellite variants, TiN monolayers, and multi-layered Ti-TiN and Ti-TiSiCN—were deposited on turbine alloys (Ti-6Al-4V, 17-4 PH, Custom-450, and Type 403 stainless steel) for screening. Unlike conventional deposition methods (APS, LPPS, CVD, PVD), PEMS employs high-current-density plasma and heavy ion bombardment for superior adhesion and microstructure density. A novel approach using trimethylsilane gas successfully produced TiSiCN nanocomposites. Stellite coatings showed no erosion improvement and were discontinued, but other hard coatings demonstrated exceptional erosion resistance—up to 25 times better than uncoated substrates and 20 times better than traditional nitride coatings. This paper details the deposition process, coating properties, adhesion tests, and characterization via SEM-EDS, XRD, nanoindentation, and sand erosion tests.

A paste, which contains Pt or Pt-xIr (x = 0-30 at%) alloy nano-powder was sprayed on some Ni-based single crystal superalloys. Then the annealing diffusion treatment at 1100 °C for 1 h in flowing Ar atmosphere was conducted to develop Pt and Pt-Ir diffusion coatings. Cyclic oxidation tests were carried out at 1150 °C in still air in order to investigate the thermal stability and oxidation behavior of the coatings and they were compared with electroplated diffusion coatings. It was found that Ir can retard the formation of voids in both the coatings and substrates. In addition, by replacing the electroplating method to the paste coating method, the crack problem due to the brittle feature of electroplated Pt-Ir coatings could be solved. Therefore, the Pt-Ir diffusion coating prepared by the paste- coating method is promising as the bond-coat material due to suppression of voids, cracks and stable Al 2 O 3 on the surface. The Pt-Ir paste diffusion coatings introduced above have several further advantages: they are easy to recoat, cause less damage to substrates, and offer comparable oxidation resistance. Thus, the method can be applicable to the remanufacturing of blades, which may extend the life of components. The future aspect of the paste coating will also be discussed.

High-pressure valves and fittings used in coal-fired 600/625 °C power plants are hardfaced for protection against wear and corrosion and to provide optimum sealing of the guides and seats. Stellite 6 and Stellite 21 are often used for hardfacing, which is carried out by build-up welding, usually in several layers. The valve materials are generally heat-resistant steels such as 10CrMo9-10 (1.7380), X20CrMoV1 (1.4922), or Grade 91 / Grade 92 (1.4903 / 1.4901). In recent years, cracks or delaminations have frequently occurred within the hardfaced layer. The influence of cycling operation is not well understood. Other essential factors are the chemical composition of the base material and of the filler metal; especially in terms of the resulting iron dilution during the deposition of the welding overlays. The research project was initiated to investigate the crack and delamination behavior and to understand the involved damage mechanisms. Thermostatic and cyclic exposure tests have shown that cracking is favored by the formation of brittle phases due to iron dilution from the substrate material during the manufacturing process. Recommendations for the welding process of hardfaced sealing surfaces of fittings were derived from the investigation results.

This presentation compares the corrosion resistance of uncoated Haynes 230 and SS316HS substrates to the same substrates coated with a Fe-based amorphous alloy. The substrates were exposed to highly corrosive media, FLiNaK, for 120 hours at 700 °C. The findings indicate that the thermal spray amorphous alloy coating provided superior corrosion resistance within the coatings while protecting the substrates against the aggressive environment. As a result, the new amorphous metal coating improved the substrate's lifespan by providing better protection against high-temperature corrosion, paving the way for a more efficient and cost-effective future in various industrial applications.

Coatings are an essential part of the materials system to protect the turbine blades from oxidation and corrosive attack during service. Inter-diffusion of alloying elements between a turbine blade substrate and their coatings is a potential concern for coated turbine blades at ever increasing operating temperatures because this can cause the formation of undesirable Secondary Reaction Zones (SRZs), which may degrade the mechanical properties of coated Ni-based superalloys. Understanding the effects of each element on the SRZ formation is essential in order to understand both the mechanism and inter-diffusion behaviour between coatings and substrates. In this research, a number of simpler aluminized ternary Ni-Al-X (where X is Co, Cr, Re, Ru or Ta) alloys were investigated in order to elucidate the separate effects of each element on the microstructural evolution, especially at the coating/substrate interface. The aluminized ternary alloys developed distinctive diffusion zones, depending on the third alloy element, ‘X’. Specifically, it has been found that both Ni-Al-Re and Ni-Al-Ta alloys developed a continuous SRZ-like diffusion layer. This diffusion zone persisted in the Ni-Al-Re alloys after high temperature exposure, indicating that Re has a stronger effect on SRZ formation than Ta.

A combination of creep tests, ex-service blade samples, thermodynamic equilibrium calculations, combined thermodynamic and kinetic calculations, image analysis, chemical composition mapping and heat treatments have been conducted on PWA1483 to determine if microstructural rejuvenation can be achieved when taking the presence of oxidation coatings into account as part of a blade refurbishment strategy. The work has shown that the γ′ morphology changes during creep testing, and that through subsequent heat treatments the γ′ microstructure can be altered to achieve a similar γ′ size and distribution to the original creep test starting condition. Thermodynamic equilibrium calculations have been shown to be helpful in determining the optimum temperatures to be used for the refurbishment heat treatments. The interaction of oxidation resistant coatings with the alloy substrate and refurbishment process have been explored with both experimental measurements and coupled thermodynamic and kinetic calculations. The predictive nature of the coupled thermodynamic and kinetic calculations was evaluated against an ex-service blade sample which had undergone refurbishment and further ageing. In general there was good agreement between the experimental observations and model predictions, and the modelling indicated that there were limited differences expected as a result of two different refurbishment methodologies. However, on closer inspection, there were some discrepancies occurring near the interface location between the coating and the base alloy. This comparison with experimental data provided an opportunity to refine the compositional predictions as a result of both processing methodologies and longer term exposure. The improved model has also been used to consider multiple processing cycles on a sample, and to evaluate the coating degradation between component service intervals and the consequences of rejuvenation of the blade with repeated engine exposure. The results from the experimental work and modelling studies potentially offer an assessment tool when considering a component for refurbishment.

An iron aluminide (Fe 3 Al) intermetallic coating was deposited onto F22 (2.25Cr-1Mo) steel substrate using a JP-5000 high velocity oxy-fuel (HVOF) thermal spray system. The as-sprayed coating was characterized by electron microscopy, X-ray diffraction, oxidation, and adhesion. Fe 3 Al coated steel specimens were exposed to a mixed oxidizing/sulfidizing environment of N 2 -10%CO-5%CO 2 -2%H 2 O-0.12%H 2 S (by volume) at 500, 600, 700, and 800°C for approximately seven days. All specimens gained mass after exposure, inversely proportional to temperature increases. Representative cross-sectioned specimens from each temperature underwent scanning electron microscopy (SEM) and X-ray mapping examination. Results are presented in terms of corrosion weight gain and product formation. The research evaluated the effectiveness of an HVOF-sprayed Fe 3 Al coating in protecting a steel substrate exposed to a fossil energy environment.

While the water vapor content of the combustion gas in natural gas-fired land based turbines is ~10%, it can be 20-85% with coal-derived (syngas or H 2 ) fuels or innovative turbine concepts for more efficient carbon capture. Additional concepts envisage working fluids with high CO 2 contents to facilitate carbon capture and sequestration. To investigate the effects of changes in the gas composition on thermal barrier coating (TBC) lifetime, furnace cycling tests (1h cycles) were performed in air with 10, 50 and 90 vol.% water vapor and in CO 2 -10%H 2 O and compared to prior results in dry air or O 2 . Two types of TBCs were investigated: (1) diffusion bond coatings (Pt diffusion or simple or Pt-modified aluminide) with commercially vapor-deposited yttria-stabilized zirconia (YSZ) top coatings on second-generation superalloy N5 and N515 substrates and (2) high velocity oxygen fuel (HVOF) sprayed MCrAlYHfSi bond coatings with air-plasma sprayed YSZ top coatings on superalloy X4 or 1483 substrates. In both cases, a 20-50% decrease in coating lifetime was observed with the addition of water vapor for all but the Pt diffusion coatings which were unaffected by the environment. However, the higher water vapor contents in air did not further decrease the coating lifetime. Initial results for similar diffusion bond coatings in CO 2 -10%H 2 O do not show a significant decrease in lifetime due to the addition of CO 2 . Characterization of the failed coating microstructures showed only minor effects of water vapor and CO 2 additions that do not appear to account for the observed changes in lifetime. The current 50°-100°C de-rating of syngas-fired turbines is unlikely to be related to the presence of higher water vapor in the exhaust.

Extended storage of spent nuclear fuel (SNF) in intermediate dry cask storage systems (DCSS) due to lack of permanent repositories is one of the key issues for sustainability of the current domestic Light Water Reactor (LWR) fleet. The stainless steel canisters used for storage in DCSS are potentially susceptible to chloride-induced stress corrosion cracking (CISCC) due to a combination of tensile stresses, susceptible microstructure, and a corrosive chloride salt environment. This research assesses the viability of the cold-spray process as a solution to CISCC in DCSS when sprayed with miniature tooling within a characteristic confinement in two different capacities: cleaning and coating. In general, the cold-spray process uses pressurized and preheated inert gas to propel powders at supersonic velocities, while remaining solid-state. Cold-spray cleaning is an economical, non-deposition process that leverages the mechanical force of the propelled powders to remove corrosive buildup on the canister, whereas the cold spray coating process uses augmented parameters to deposit a coating for CISCC repair and mitigation purposes. Moreover, both processes have the potential to induce a surface compressive residual stress that is known to impede the initiation of CISCC. Surface morphology, deposition analysis, and microstructural developments in the near-surface region were examined. Additionally, cyclic corrosion testing (CCT) was conducted to elucidate the influence of cold-spray cleaning and coating on corrosion performance.

Steam turbine is one of the critical equipments in coal-fired power plants, steel P91 is a common material of its control valves. CoCr-based hardfacing on valve seats can resist long time exposure to water vapor with high temperature, thermal fatigue and solid particles erosion under high pressure. However, these hardfacing can crack and disbond during operation, which generates high risks for turbine systems and power plants. This article discussed the failure reasons of CoCr-based hardfacing, and introduced a method and practical experience of on-site repairing steam turbine valve seats with laser cladding NiCr coating.

Because of the problems experienced with steam-side oxide scale exfoliation in commercial power plants, there has been increased interest in understanding the steam oxidation resistance of 300- series stainless steels such as 347H and 304H. Model alloys were used in an attempt to understand the effect of varying Ni (9-12%) and Cr (16-20%) on steam oxidation resistance at 650°C. However, the model alloys generally showed superior oxidation resistance than commercial alloys of similar composition. Several surface engineering solutions also were investigated. The commercially favored solution is shot peening. Laboratory steam testing at 650°C found that annealing temperatures of ≥850°C eliminated the benefit of shot peening and a correlation was observed with starting hardness in the peened region. This effect of annealing has implications for the fabrication of shot peened tubing. Another route to improving oxidation resistance is the use of oxidation resistant diffusion coatings, which can be deposited inexpensively by a vapor slurry process. Uniform coatings were deposited on short tube sections and annealed at 1065°C to retain good 650°C creep properties. The coating was thicker than has been investigated in laboratory processes resulting in increased brittleness when the coating was assessed using 4-point bending.

The steam oxidation behaviour of boiler tubes and steam piping components is a limiting factor for improving the efficiency of the current power plants. Spallation of the oxide scales formed during service can cause serious damage to the turbine blades. Vallourec has implemented an innovative solution based on an aluminum diffusion coating applied on the inner surface of the T/P92 steel. The functionality of this coating is to protect the tubular components against spallation and increase the actual operating temperature of the metallic components. In the present study, the newly developed VALIORTM T/P92 product was tested at the EDF La Maxe power plant (France) under 167b and 545°C (steam temperature). After 3500h operation, the tubes were removed and characterized by Light Optical Metallography (LOM), Scanning Electron Microscopy (SEM), with Energy Dispersive X-ray spectrometry (EDX) and X-Ray Diffraction (XRD). The results highlight the excellent oxidation resistance of VALIORTM T/P92 product by the formation of a protective aluminum oxide scale. In addition, no enhanced oxidation was observed on the areas close to the welds. These results are compared with the results obtained from laboratory steam oxidation testing performed on a 9%Cr T/P92 steel with and without VALIORTM coating exposed in Ar-50%H 2 O at 650°C.

In order to meet the 2010-2020 DOE Fossil Energy goals for Advanced Power Systems, future oxy-fuel and hydrogen-fired turbines will need to be operated at higher temperatures for extended periods of time, in environments that contain substantially higher moisture concentrations in comparison to current commercial natural gas-fired turbines. Development of modified or advanced material systems, combined with aerothermal concepts are currently being addressed in order to achieve successful operation of these land-based engines. To support the advanced turbine technology development, the National Energy Technology Laboratory (NETL) has initiated a research program effort in collaboration with the University of Pittsburgh (UPitt), and West Virginia University (WVU), working in conjunction with commercial material and coating suppliers as Howmet International and Coatings for Industry (CFI), and test facilities as Westinghouse Plasma Corporation (WPC) and Praxair, to develop advanced material and aerothermal technologies for use in future oxy-fuel and hydrogen-fired turbine applications. Our program efforts and recent results are presented.

NAC International Inc. (NAC) is providing transportable storage canisters (TSCs) to Central Plateau Cleanup Company CPCCo) for long term dry storage of capsulized radioactive waste at the Hanford Site in Richland, WA. The TSC consists of 316/316L stainless-steel components welded to form a cylindrical canister that acts as a confinement boundary for the payload. The heat affected zones of the welded areas are most susceptible to Chloride Induced Stress Corrosion Cracking (CISCC), that may limit the life of the TSC. To mitigate CISCC during the anticipated 300-year storage period, an overcoating is applied to the heat affected zones of all external TSC fabrication welds, referred to as Cold Spray. This paper will discuss the purpose, development, and application of Cold Spray to the CPCCo TSCs. Cold Spray is a process whereby metal powder particles are deposited upon a substrate by means of ballistic impingement via a high-velocity stream of gas, resulting in a uniform deposition with minimal porosity and high bond strength. Temperatures are below the melting thresholds of many engineering materials enabling a large variety of application uses. NAC developed a process for Cold Spray application onto the 316/316L stainless-steel TSCs to serve as a CISCC protective/mitigative coating for its canister products. Testing during development arrived at nickel as the deposited coating material and nitrogen as the gas vehicle, along with a set of various application parameters. The qualified process was implemented onto the CPCCo TSCs. Prior to application, the equipment and process are validated via coupons that are sprayed and then tested to meet requirements for adhesion strength (ASTM C633) and porosity (ASTM E2109). After successful coupon testing, Cold Spray is performed on the external TSC fabrication welds, to include heat affected zones. Acceptance testing of the resulting deposition is performed via visual inspection.