ICMCTF2013 Session A1-2: Coatings to Resist High Temperature Oxidation, Corrosion and Fouling

Monday, April 29, 2013 1:30 PM in Room San Diego
Monday Afternoon

Time Period MoA Sessions | Abstract Timeline | Topic A Sessions | Time Periods | Topics | ICMCTF2013 Schedule

Start Invited? Item
1:30 PM A1-2-1 Oxidation Behavior of Co-Doped NiCrAl Alloys in Dry and Wet Air
Kinga Unocic, Bruce Pint (Oak Ridge National Laboratory, US)

Cast NiCrAl alloys with additions of Y, La, Hf and Ti were evaluated at 1100°C in wet (10 and 50% H2O) and dry air in order to optimize such dopants for superalloy bond coatings. The results suggest that the typical Y addition in most coatings could be replaced by La. Also, scale adhesion in cyclic testing was improved with the co-addition of Hf with La or Y. Ti was added to investigate its incorporation in coatings on superalloys containing significant Ti additions. Particularly with co- doped alloys, the addition of Ti had little effect. Water vapor increased spallation, especially for the least adherent alloys, such as Y,Ti-doped NiCrAl, water vapor increased scale spallation. For the co- doped compositions with Hf, water vapor had a limited effect on scale adhesion on the alumina growth rate in isothermal exposures. In addition to specimen mass change, beta phase depletion in the substrate was evaluated. Analytical transmission electron microscopy showed that Y, La and Hf co- segregated to the alumina scale grain boundaries and formed dopant rich oxide precipitates in the scale.

Research sponsored by the U. S. Department of Energy, Office of Fossil Energy, Coal and Power R&D.

1:50 PM A1-2-2 Platinium Diffusion in Pure Nickel
Maryana Zagula-Yavorska, Jolanta Romanowska, Jan Sieniawski (Rzeszów University of Technology, Poland)

The diffusion behavior of Pt deposited on pure nickel by the electroplating process was examined by the analysis of Pt concentration profiles against the distance in pure nickel specimens for various diffusion times (2, 4, 6, 8, 10, 12 and16 hours) at 1323K. Platinum diffusion coefficient was calculated by the use of the finite differences method. In solving the equations, it was accepted , that for a c(x) function, it is possible to approximate its derivative (slope/tangent) at a certain point by: the slope of the arc described as the difference of functions at the end of the calculation area or by the slope of the arc described as a reverse difference of functions – close to the samples surface;or by the slope of AB arc given as a central difference of functions – inside the sample. The platinum diffusion coefficient varied from 2.28x10-14 (for 2 hours) to 8.96x10-14(for 16 hours). The thickness of the diffusion zone is proportional to the a power function of the diffusion time. The exponent m of the power function is 0.4. As the m coefficient is slightly smaller than 0.5, we may expect, that the volume diffusion predominantly controls the layer growth and the boundary diffusion lightly contributes to the rate- controlling process.

2:10 PM A1-2-3 Microstructure Degradation of EB-PVD TBCs on Pt and Pd/Pt-modified Aluminide Coatings under Cyclic Oxidation Conditions
Radoslaw Swadzba (Institute for Ferrous Metallurgy, Poland)

The study concerns comparison of Pt and Pd/Pt-modified aluminide bond coatings for

EB-PVD TBCs on N5 superalloy in terms of microstructural evolution during cyclic oxidation tests.

The coatings were deposited by Pt and Pd+Pt electroplating, followed by high activity vapor phase aluminizing at 1050°C and pre-oxidation heat treatment in order to form α-alumina TGO. The 7wt.% yttria stabilized zirconia TBC was deposited using electron beam physical vapor deposition. Cyclic oxidation tests of the coatings were performed at 1100°C in 1h cycles in laboratory air. The microstructures of the coatings in the as-deposited state as well as after cyclic oxidation tests were studied using SEM, EDS and EBSD. The evolution and phenomena occurring at the interface between the bond coating, thermally grown oxide and TBC during high temperature exposure were studied in detail using high resolution CTEM and S/TEM. The samples for S/TEM analysis were prepared using FIB (Focused Ion Beam). The study is mostly focused on the growth of TGO during high temperature exposure and the overall performance of the Pd/Pt-modified aluminide coatings as a cost effective alternative to Pt-modified aluminide coatings commonly used as EB-PVD bond coats.

2:30 PM A1-2-4 Ferritic-Martensitic Steels: Improvement of the Oxidation Behavior in Steam Environments via Diffusion Coatings
Diana Schmidt, Mathias Galetz, Michael Schütze (DECHEMA-Forschungsinstitut, Germany)

Modern heat resistant ferritic-martensitic steels are of high interest as superheater materials in fossil fuel power plants. They have much better heat transfer behavior and a lower coefficient of thermal expansion, as well as lower costs in comparison to austenitic steels and nickel base alloys. Modern 9% Cr-steels have sufficient creep strength up to 650°C, however their corrosion resistance particularly in H2O containing environments needs further improvement. The inner side of the superheater tubes is exposed to steam, which leads to increased corrosive attack.

Results pertaining to the enrichment of chromium and manganese in the metal subsurface region of P91 and P92 using a diffusion process (pack cementation) without altering the bulk phase will be presented. The diffusion treatment developed is based on thermodynamic considerations for the design of the coating process. High temperature oxidation exposure of uncoated and coated samples at 650°C in argon with 50% H2O, a gas which was shown before to yield the same oxidation behavior such as pure steam oxidation, shows the improved behavior. The paper discusses the coating process parameters and the oxidation behavior.

2:50 PM Invited A1-2-5 Oxidation under Pure Steam: Protective Oxides and Coatings
Alina Agüero, Vanessa González, Marcos Gutiérrez (Instituto Nacional de Técnica Aeroespacial, Spain); Raúl Muelas (Ingeniería y Servicios Aeroespaciales, Spain)
Although at temperatures of 900º C and higher, the formation, transformation and failure of protective oxides in air has been deeply studied, there is significantly less available information of these processes when they take place under pure steam and in the lower temperature range pertinent to steam power plants. New designs for these plants are expected to operate at 625-700º C, at which the candidate ferritic/martensitic steels exhibit very low steam oxidation resistance. In this paper, available knowledge of the behaviour of protective oxides formed under steam at 650º C will be presented. It is already known that on ferritic/martensitic steels with a Cr content lower than ~9 wt. % in Cr, such as P22, CB2, P91 and P92, a non protective, thick dual later composed of Fe3O4 and (Fe, Cr)3O4 forms. However, significantly higher steam oxidation resistance has been recently found when exposing NPM1, a 9 wt. % Cr martensitic steel rich in W and Co, to pure steam at 650º C. In this case a protective, very thin multilayer forms, with alternating Fe3O4 and (Fe, Cr, Mn)3O4. Fe based, Cr rich coatings, both diffusion and overlay, develop in most cases a protective spinel, which may also contain Cr2O3 depending on the Cr content. On the other hand, Cr containing coatings based on Ni may develop a very stable, protective thin Cr2O3 layer. In addition, in both Fe and Ni based coatings, the formation of a thin protective Cr rich oxide is affected by other elements present in the material. Finally, on Al containing coatings, such as Fe aluminides and FeCrAls, Al2O3 forms under steam at 650º C. Provided that a critical content of Al is maintained underneath the scale, Al2O3 is very stable, surpassing 40,000 h under steam at 650º C, without evidence of spallation. In turn, the critical Al content depends on the coating’s Cr content, as it happens when oxidation takes place at temperatures of 900º C or higher, under air. However, under steam, alumina phases formation and transformations are different, as at 650º C χ-Al2O3 forms initially, slowly transforming into α-Al2O3. General considerations regarding the stability of protective oxides formed under steam as a function of the composition of the subjacent material will be provided.
3:30 PM A1-2-7 Investigation of the Anti-adhesion Effect of Nano- and Micro-structured Surfaces
MariadelMar Juez Lorenzo, Vladislav Kolarik, Raquel Roussel, Veronica Kuchenreuther (Fraunhofer ICT, Germany); Francisco Velasco (Universidad Carlos III-Madrid, Spain); Susana Guzman (Universidad Carlos III- Madrid, Spain); Fernando Pedraza (Université de la Rochelle, France)
The reduction of adhesion of corrosive deposits on high temperature material surfaces bears a considerable potential to reduce damage by corrosion. The effect of nano- and micro-structuring the surface by coating with spherical Al particles was studied in the frame of the European project PARTICOAT. These coatings form with an appropriate heat treatment a surface with nano- or microstructures similar to the Lotus leaf structure. Alloy 321 and IN738 were coated with Al particles with a size between 1 and 20 µm and a heat treatment between 650°C and 950°C was applied, yielding surfaces with needle-like structures. A salt with 40% Na2SO4 and 60% V2O5, molten and solidified prior to the experiment, was deposited on the coated surface. The samples were then heated in air from room temperature to 675°C with a heating rate of 10°C/min. The sample surface was observed in situ with a video camera revealing the melting of the salt and its interaction with the surface. The analysis of the sample surface as well as the cross-section was performed by optical microscopy, SEM and EDX. The surface region of the coating is infiltrated by the molten salt. In the case of Alloy 321, the infiltrated coating layer is partially detached from the remaining un-affected coating, which may provide a predetermined delamination section for the salt drop. Contact with the metal surface was not observed within the experimentation times. Surface structures with fine long filaments with a thickness of approximately 110 nm showed the lowest infiltration depth of the salt into the coating.
3:50 PM A1-2-8 Chloride Induced High Temperature Corrosion in Waste and Biomass Fired Boilers – Degradation Mechanisms and Mitigation Measures
Torbjörn Jonsson, Jesper Liske, Jan-Erik Svensson, Lars-Gunnar Johansson (Chalmers University of Technology, Sweden)

The fireside environment in power boilers may be quite corrosive, especially in boilers firing biomass and waste, where the fireside environment is characterized by a combination of high levels of reactive alkali (NaCl and KCl), HCl and relatively low SO2 concentrations. The corrosion problems shorten the lifetime of the waterwall and the steam superheater, limiting the maximum steam temperature. This paper presents new results on the mechanism behind the accelerated high temperature corrosion suffered by stainless steel and low alloyed steel in the presence of alkali chlorides, O2 and H2O. We also discuss different measures to mitigate the corrosion problems in real boilers. Thus, sulphur can be added to the fuel in order to convert the alkali chlorides to the corresponding alkali sulphates, which are far less corrosive. Another opportunity to increase the lifetime of the boiler is to apply coatings or use alloys that are optimized with respect to chloride-induced corrosion. This work is mainly based on laboratory investigations of corrosion but will also make comparisons with corrosion experiments in real boilers.

4:10 PM A1-2-9 Properties and Performance of Al/Al2O3 Coatings on 304 Steel in Metal Dusting Environments
Esmeralda Uribe (EGIC, Mexico); Olimpia Salas, Joaquin Oseguera, Dulce Melo-Maximo (ITESM-CEM, Mexico); CARLOSMAURICIO Lepienski (UFPR, Brazil); Ricardo Diego Torres (PUCPR, Brazil); Roberto De Souza (Usp, Brazil)
Al/Al2O3 thin films were produced by reactive magnetron sputtering on 304 stainless steel substrates to investigate the effect of various deposition parameters on the structural evolution and properties of the films and their performance as protective coatings in metal dusting environments. Selected deposition parameters included: level of oxygen flow, rate of oxygen feeding and application of bias voltage to the substrate. The resulting films were characterized by optical microscopy, scanning electron microscopy + energy dispersive analysis, and x-ray diffraction, and their adhesion by scratch testing. The coatings were then subjected to a carburizing atmosphere at high temperature in a thermobalance to evaluate their response to metal dusting. The results indicate that the coatings present good adhesion and density which are desirable for their present application.
4:30 PM A1-2-10 Microstructural Evolution of Cr/Cr2O3 coatings during exposure to Metal Dusting conditions
Lizbeth Melo-Maximo (Instituto Politécnico Nacional, Mexico); Olimpia Salas (ITESM-CEM, Mexico); VictorManuel Lopez-Hirata (Instituto Politécnico Nacional, Mexico); Dulce Melo-Maximo, Joaquin Oseguera (ITESM-CEM, Mexico); Ricardo Diego Torres (PUCPR, Brazil); Roberto De Souza (Usp, Brazil)
An extensive microstructural characterization of Cr/Cr2O3 thin films deposited on 304 substrates after exposure to highly carburizing conditions was carried out in order to investigate the role of these coatings in protection against metal dusting. The films were produced by reactive magnetron sputtering. The effect of bias voltage application as well as the partial pressure of oxygen on the structure and properties of the films was investigated. Promissing films as well as uncoated substrates were then exposed to a carburizing atmosphere at high temperature for various times to follow and compare the structural changes on the surface of the samples.
4:50 PM A1-2-11 High-temperature Oxidation Corrosion of Boiler Steel with Al Coating under Co-firing of Biomass Charcoal / Coal Deposits
Cheng-Yi Tung, Chaur-Jeng Wang, Shih-Pao Wen (National Taiwan University of Science and Technology, Taiwan, Republic of China)
The study the SA209-T1 and SA213-T22 boiler steel with Al coating, in different proportions 24-120 hours at 600 ° C by mixed burning biomass charcoal / coal in order to investigate the high-temperature corrosion of the fly ash deposition of sedimentary fuel. Not Al coating boiler steel Experimental results show that the deposition of co-firing biomass charcoal / coal for T1 and T22 steel materials of high-temperature corrosion mechanisms, the initial period of biomass charcoal or coal has not been released from combustion of sulfur, chlorine and other elements, for simple high-temperature oxidation behavior. The lack of chromium T1, of KCl impact occur the accelerated oxidation insignificant, but the overall corrosion is still better than chromium steel is sourced serious. With the growth of the time, its role in sulfur chlorine ingredients within the fuel consumed via reaction the more gentle, mainly late corrosion behavior of the two kinds of steel materials are based on high-temperature oxidation. This study is enhancing resistance to high temperature oxidation and corrosion by the Al coating boiler steel.
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