Persona: Muelas Gamo, Raúl
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Instituto Nacional de Técnica Aeroespacial
El Instituto Nacional de Técnica Aeroespacial es el Organismo Público de Investigación (OPI) dependiente del Ministerio de Defensa. Además de realizar actividades de investigación científica y de desarrollo de sistemas y prototipos en su ámbito de conocimiento, presta servicios tecnológicos a empresas, universidades e instituciones.
El INTA está especializado en la investigación y el desarrollo tecnológico, de carácter dual, en los ámbitos de la Aeronáutica, Espacio, Hidrodinámica, Seguridad y Defensa.
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Muelas Gamo
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Publicación Restringido Comparison between field and laboratory steam oxidation testing on aluminide coatings on P92(Wiley online library, 2011-01-12) Agüero, Alina; González, V; Gutiérrez del Olmo, Marcos; Knödler, R; Straub, S; Muelas Gamo, Raúl; Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737Steam oxidation has become an important issue for steam power plants as operating temperatures increase from the current 550 to 600–650 °C. For the last 10 years several groups have been carrying out steam oxidation testing of both uncoated substrates and coatings in the laboratory. On the other hand, field testing results are very scarce. In this paper, a comparison of laboratory steam oxidation testing with field test results carried out by Alstom at the Kraftwerk Westfalen power station located in Hamm, Germany will be presented. Both slurry deposited aluminide coatings and uncoated P92 steel have been included in the study. Under steam (atmospheric pressure) and isothermal conditions in the laboratory at 650 °C, spallation of oxides formed on ferritic steels occurs after significantly longer time when compared to exposure to real operating conditions. Oxide spallation results in serious damage in steam power plants by obstructing heat exchanger tubes, erosion of valves and turbine blades, etc. Moreover, the thickness of the oxide scales formed under field testing conditions is significantly higher after similar exposure. On the other hand, aluminide coated P92, which exhibit thickness through cracks, have shown to be stable in the laboratory for up to 60 000 h at 650 °C under steam, without evidence of crack propagation. However, field test results indicate that some degree of crack propagation occurs but without causing substrate attack up to 21 700 h of exposure. Moreover, the aluminium oxide observed in both laboratory and field tested specimens is different.Publicación Restringido HVOF coatings for steam oxidation protection(Wiley online library, 2008-05-29) Agüero, Alina; Muelas Gamo, Raúl; González, Vanessa; Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737In the context of the European project ‘Coatings for Supercritical Steam Cycles’ (SUPERCOAT), the use of steam oxidation resistant coatings on currently available ferritic materials with high creep strength but poor oxidation resistance was investigated in order to allow increase in the operating temperature of steam power plants from 550 to 650 °C. Among the explored coating techniques for this application, chosen on the basis of being potentially appropriate for coating steam turbine components, High Velocity Oxy Fuel (HVOF) thermal spray has resulted in one of the most successful techniques. Different alloyed materials such as FeCrAl, NiCrSiFeB, FeAl, NiCr and FeCr have been deposited, optimized and tested under flowing steam at 650 °C. Characterization of as deposited and tested samples by metallography, SEM-EDS and XRD was carried out. Some of these coatings form protective pure chromium or aluminium oxides exhibiting excellent behaviour for at least 15 000 h of exposure, whereas others form less stable complex mixed oxides which nevertheless grow at considerably slower rates than the oxides formed on uncoated P92 (9 wt% Cr ferritic steel).Publicación Restringido Cyclic oxidation and mechanical behaviour of slurry aluminide coatings for steam turbine components(Elsevier, 2007-04-02) Agüero, Alina; Muelas Gamo, Raúl; Gutiérrez del Olmo, Marcos; Van Vulpen, R.; Osgerby, Steve; Banks, J. P.The excellent steam oxidation resistance of iron aluminide coatings on ferritic steels at 650 °C has been demonstrated both by laboratory tests and field exposure. These coatings are formed by the application of an Al slurry followed by diffusion heat treatment at 700 °C for 10 h. The resulting microstructure is mostly composed of Fe2Al5 on top of a much thinner FeAl layer. This coating exhibits perpendicular cracks due to thermal expansion mismatch between coating and substrate. However, these stress relieving cracks do not seem to have an effect on the mechanical properties of the substrate. Cyclic oxidation, creep resistance and TMF testing of these coatings at 650 °C indicate excellent performance.Publicación Acceso Abierto Slurry and Thermal Spray Coatings for Protection of New Generation Steam Engine Components(ASM International, 2001-03-14) Agüero, Alina; Muelas Gamo, Raúl; Román Gárate, AliciaPublicación Restringido Al Slurry Coatings for Molten Carbonate Fuel Cell Separator Plates(Scientific.Net, 2001-01-20) Agüero, Alina; García, M. C.; Muelas Gamo, Raúl; Sánchez, A.; Pérez, Francisco J.; Duday, David; Hierro, M. P.; Gómez, ConsueloThe corrosion behaviour of Al slurry coated AISI 310 stainless steel, with and without diffusion heat treatment, was investigated as a wet seal material for molten carbonate fuel cell (MCFC) at 650°C. The results were compared with IVD Al coated AISI 310. Characterization of the samples before and after exposure to the eutectic 62 mol% Li2CO3-38 mol% K2CO3 mixture at 650°C for 1000 h by SEM-EDS and XRD was carried out. The presence of LiAlO2 on the coated samples was confirmed by XRD. The slurry Al-coated stainless steels performed at least as well as the IVD Al coating.Publicación Restringido Steam Oxidation Resistant Coatings for Steam Turbine Components: A Feasibility Study(Scientific.Net, 2001-10-20) Agüero, Alina; García de Blas, Javier; Muelas Gamo, Raúl; Sánchez, A.; Tsipas, Sophia A.The principal objective of the COST Action 522 is to raise the operating temperatures of both gas and steam turbines in order to increase their efficiency to reduce fuel consumption and emissions. Concerning steam turbines, the operating temperature is expected to rise from 550°C to 650°C, and the use of oxidation resistant coatings is being considered for the first time in Europe. In this preliminary work, two deposition techniques have so far been explored: slurry paints and atmospheric plasma spray (APS). Commercially available materials, known to have good oxidation resistance, were selected for both deposition techniques: one aluminium slurry and three alloyed materials for thermal spray: AlFe, FeCrAl and NiAl. The coatings were characterised by SEM-EDS and steam oxidation testing was carried out at 650°C. The preliminary findings show that some of the studied coatings may offer adequate protection.Publicación Restringido Steam Oxidation Testing of Coatings for Next Generation Steam Power Plant Components(Scientific.Net, 2006-08-14) Agüero, Alina; Gutiérrez del Olmo, Marcos; Muelas Gamo, RaúlTo achieve higher power generation efficiency in steam turbines, operating temperatures are expected to rise from 550°C to 650°C. The use of oxidation resistant coatings on currently available materials, with high creep strength but inferior steam oxidation resistance, is being explored in order to accomplish this goal in the context of the European project “Coatings for Supercritical Steam Cycles” (SUPERCOAT). Coating techniques have been chosen on the basis of being potentially appropriate for coating steam turbine components: the application of metallic and ceramic slurries, pack cementation and the deposition of alloyed and cermet materials by thermal spray. The coatings were characterised by metallography, SEM-EDS and XRD and steam oxidation and thermal cycling laboratory testing was carried out at 650º C. In this presentation, the testing results of selected coatings will be shown including those which exhibit the most promising behaviour. For instance, slurry aluminides have been exposed to steam at 650°C for more than 38,000 h (test ongoing) without evidence of substrate attack. Some HVOF coatings such as FeAl, NiCr and FeCr also have shown excellent behaviour. The results have provided information regarding the mechanism of protection and degradation of these coatings as well as insight into new coating development.Publicación Restringido Steam Oxidation of Slurry Aluminide Coatings on Ferritic Steels for Advanced Coal-Fired Steam Power Plants(Scientific.Net, 2004-08-12) Agüero, Alina; Muelas Gamo, RaúlThe use of slurry aluminide coatings on ferrite steels for advanced coal-fired steam power plants were analyzed. The materials used were found to have good high temperature oxidation resistance and deposited by techniques that can be employed to coat large steam turbine components either at the plant or at their location of manufacture. Laboratory steam oxidation testing as well as characterization of the coatings both before and after exposure was also presented. The results have provided information regarding the mechanism of protection and degradation of these coatings as well as insight for new coating development.Publicación Restringido Thermal spray coatings for molten carbonate fuel cells separator plates(Elsevier, 2001-10-30) Agüero, Alina; García de Blas, Javier; García, M. C.; Muelas Gamo, Raúl; Román Gárate, AliciaMolten salt corrosion at the wet seal of separator plates is one of the principal life-limiting factors of molten carbonate fuel cells (MCFC). The wet seal must therefore be coated with an aluminide layer that is commonly produced by ion vapor deposition (IVD) of Al followed by heat treatment. However, this coating only lasts approximately 20 000 h and not the 40 000 h expected for a cell life. Moreover, the IVD Al coating is also very expensive since only a few plates can be coated simultaneously due to size limitations of the existing commercial vacuum chambers employed in IVD. The need of heat treatment further increases costs, particularly since it requires long heating and cooling cycles in order to minimize distortion of the thin stainless steel plates. Thermally sprayed coatings constitute an alternative that requires neither containment nor heat treatment, and also provides the possibility of depositing materials more resistant to molten carbonates than plain aluminides. However, separator plates coated by thermal spray suffer distortion, due both to sand blasting (usually required prior to coating), and to the heat transfer process that occurs during the spraying process. In this work, commercially available coatings have been applied by plasma spray and high velocity oxyfuel (HVOF), employing alternative surface preparation methods. Moreover, substrate pre-heating and/or cooling during deposition were examined in order to eliminate substrate distortion. FeCrAl, and NiAl as well as a quasi-crystalline approximant alloy AlCoFeCr were deposited on AISI 310 foils, and after optimization the resulting coatings were characterized by means of scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). The optimized coatings were then tested by immersion in a 62 mol.% Li2CO3/38 mol.% K2CO3 molten carbonate eutectic mixture at 700°C and by electrochemical impedance spectroscopy. IVD Al coatings were also tested for comparison purposes. The results indicate that FeCrAl exhibits a higher molten salt corrosion resistance than IVD aluminide coatings whereas NiAl was attacked shortly after the beginning of the test. The QC approximant AlCoFeCr resisted 1000 h of attack but its composition changed. Grinding of the substrate prior to coating resulted in good adhesion and substrate distortion was minimized by Ar cooling during deposition.Publicación Restringido Long exposure steam oxidation testing and mechanical properties of slurry aluminide coatings for steam turbine components(Elsevier, 2005-11-21) Osgerby, Steve; Pastor Muro, Ana; Agüero, Alina; Muelas Gamo, RaúlImportant efforts to develop new steels or to protect high creep strength steels in order to allow operation of steam turbines at 650 °C are being carried out world-wide to increase efficiency. Within the European Project “SUPERCOAT” (Coatings for Supercritical Steam Cycles), work has been concentrated in the development of coatings to withstand 50,000–100,000 h of operation at 650 °C under high pressure steam. Aluminide coatings on ferritic–martensitic steels produced by applying an Al slurry followed by a diffusion heat treatment, have shown to be protective at 650 °C under steam for at least 32,000 h of laboratory steam exposure under atmospheric pressure. Although the “as diffused” coatings present through thickness cracks, these do not propagate during exposure to steam or thermal cycling and no new cracks seem to develop. Moreover, no changes in residual stresses could be observed after thermal cycling. Microstructural characterization of samples at different periods of exposures has been carried out by SEM-EDS and XRD. The principal mechanism of coating degradation is loss of Al at the surface due to inwards diffusion. Microhardness as well as Young's modulus and fracture strength were measured using well established techniques. The coatings show reasonable ductility (∼1.6%) when stressed in tension between room temperature and 400 °C which further increases at higher temperatures providing evidence that the coatings should withstand the mechanical conditions likely to be encountered in service.
