Persona: Agüero, Alina
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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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Publicación Restringido Long term diffusion studies in Fe aluminide coatings deposited by slurry application on ferritic steel(Scientific.Net, 2009-04-22) Agüero, Alina; González, Vanessa; Gutiérrez del Olmo, MarcosDiffusion iron aluminide coatings have shown excellent resistance to high temperature oxidation in air, corrosive atmospheres and steam. A study of the diffusion behaviour of slurry applied diffusion aluminide coatings deposited on ferritic steel have been carried out under a 100% flowing steam atmosphere for up to 50,000 h at 650 °C. The results have shown that initially, the coating forms by outward growth possibly including the dissolution of the steel in molten aluminium. At later stages, during exposure to steam at 650 °C, aluminium diffuses inward and moreover, Fe also diffuses outward resulting in the progressive development of Kirkendall porosity. Results have also indicated that in order to form a pure protective Al2O3 scale the Al wt.% has to be > 4. Below this content Al-Fe mixed oxides develop exhibiting a less protective behaviour.Publicación Restringido Aluminum slurry coatings to replace cadmium for aeronautic applications(Elsevier, 2012-10-27) Agüero, Alina; del Hoyo Gordillo, Juan Carlos; García de Blas, Javier; García, M.; Gutiérrez, M.; Madueño, L.; Ulargui, S.Cadmium has been widely used as a coating to provide protection against galvanic corrosion for steels and for its natural lubricity on threaded applications. However, it is a toxic metal and a known carcinogenic agent, which is plated from an aqueous bath containing cyanide salts. For these reasons, the use of cadmium has been banned in Europe for most industrial applications. However, the aerospace industry is still exempt due to the stringent technical and safety requirements associated with aeronautical applications, as an acceptable replacement is yet to be found. Al slurry coatings have been developed as an alternative to replace cadmium coatings. The coatings were deposited on AISI 4340 steel and have been characterized by optical and electron microscopy. Testing included salt fog corrosion exposure, fluid corrosion exposure (immersion), humidity resistance, coating-substrate and paint-coating adhesion, electric conductivity, galvanic corrosion, embrittlement and fatigue. The results indicated that Al slurry coatings are an excellent alternative for Cd replacement.Publicación Restringido Microstructural Evolution of Slurry Fe Aluminide Coatings during High Temperature Steam Oxidation(Trans Tech Publications, 2008-09-15) Agüero, Alina; Spiradek, Krystina; Höfinger, S; Gutiérrez del Olmo, Marcos; Muelas Gamo, RaúlSlurry iron aluminide coatings are very resistant to steam oxidation at 600-650º C. These coatings can be used to protect new generation Ultra Super Critical (USC) steam power plant ferritic/martensitic steel components. The microstructure of the initially deposited coating changes as a function of time, mainly due to coating-substrate interdiffusion, going from mostly Fe2Al5 to FeAl, causing the precipitation of AlN in those substrates containing a minimum content of N and moreover, developing Kirkendall porosity at the coating-substrate interface. Steam oxidation at 650º C causes the formation of a protective thin layer of hexagonal χ-Al2O3 phase along with some α- and γ-Al2O3 after the first few hours of exposure. However, despite the relatively low temperature, and after several thousands hours the protective layer was mostly composed of α-Al2O3. A study of the evolution of the microstructure of slurry aluminide coatings deposited on P92 and exposed to steam at 650º C has been carried out by scanning and transmission electron microscopy and X ray diffraction.Publicación Acceso Abierto Rapid α-Al2O3 Growth on an Iron Aluminide Coating at 600 °C in the Presence of O2, H2O, and KCl(ACS Publications, 2024-10-17) Agüero, Alina; Audigié, Pauline; Sergio, Rodríguez Catela; Gutiérrez del Olmo, Marcos; Pascual Ferreiro, Jon; Ssenteza, Vicent; Jonsson, Torbjörn; Johansson, Lars Gunnar; Agencia Estatal de Investigación (España); European CommissionIn this work, a slurry iron aluminide-coated ferritic steel SVM12 was subjected to a laboratory experiment mimicking superheater corrosion in a biomass-fired power boiler. The samples were exposed under model Cl-rich biomass conditions, in a KCl + O2 + H2O environment at 600 °C for 168, 2000, and 8000 h. The morphology of corrosion and the composition of the oxide scale and the coating were investigated by a combination of advanced analytical techniques such as FESEM/EDS, SEM/EBSD, and XRD. Even after short-term exposure, the coating developed a very fast-growing and up to 50 μm thick α-Al2O3 scale in contrast to the spontaneous formation of a protective, thin, dense, slow-growing, and very adhesive α-Al2O3 layer usually formed on metallic materials after high-temperature oxidation. In view of the literature on the formation of oxide scales on alloys and coatings, the formation of an α-Al2O3 scale at this relatively low temperature is very surprising in itself. The thick alumina scale was not protective as its formation resulted in fast degradation of the coating and rapid Fe2Al5 → FeAl phase transformation, which in turn generated porosity inside the coating. In all cases, the resulting thick Al2O3 scale was porous and consisted of both equiaxed α-Al2O3 grains and randomly oriented aggregated alumina whiskers. Potassium is concentrated in the outer part of the Al2O3 scale, while chlorine is concentrated close to the scale/aluminide interface. The unexpected formation of rapidly growing α-Al2O3 at relatively low temperature is attributed to the hydrolysis of aluminum chloride generated in the corrosion process.Publicación Restringido Deposition process of slurry iron aluminide coatings(Taylor and Francis online, 2008-10-04) Agüero, Alina; Gutiérrez del Olmo, Marcos; González, VanessaDiffusion iron aluminide coatings prevent steam oxidation of ferritic/austenitic steels at 650°C for at least 45,000 h. These coatings are deposited by applying Al slurries followed by a diffusion heat treatment at 650°C. The quality of the coatings is very sensitive to a number of factors such as surface preparation, slurry composition and diffusion treatment temperature. A study of the effect of the different processing parameters has been performed in order to optimize the process from an industrial perspective. Moreover, most commercially available Al slurries contain different levels of Cr6+, a highly carcinogenic species, and therefore Cr6+ free slurry formulations have been prepared. In addition, re-coating after exposure has also been developed since it is not clear yet if these coatings will last the 100,000 h which is the life limit for steam power plant design. Based on these studies, processes suitable for coating real size components and re-coating steam exposed components have been developed and are presented in this contribution.Publicación Restringido Hot corrosion study of coated separator plates of molten carbonate fuel cells by slurry aluminides(Elsevier, 2002-12-02) Pérez Trujillo, Francisco Javier; Duday, David; Hierro, María Pilar; Gómez de Castro, Consuelo; Agüero, Alina; García, M. C.; Muelas Gamo, Raúl; Sánchez Pascual, A.; Martínez, L.The corrosion behavior of Al coated AISI 310S stainless steel by slurry and ion vapor deposition (IVD) was investigated as an electrolyte seal material in a mounted carbonate fuel cell (MCFC) at 650 °C. The results were compared with uncoated AISI 310S stainless steel and TA6V alloy. The characterization of the samples after exposure to the eutectic 62 mol.% Li2CO3–38 mol.% K2CO3 mixture at 650 °C up to 1000 h has shown the presence of LiAlO2 (coated samples), LiFeO2 and LiCrO2 (stainless steels), and Li2TiO3 (TA6V) oxides at the scale–melt interface. The electrochemical impedance spectroscopy (EIS) technique has shown high values of polarization resistances for TA6V and lower values for coated steels. The uncoated AISI 310S stainless steel have shown the lowest polarization resistance. A mechanism for the corrosion of Al-coated stainless steels in molten carbonate is proposed taking into account thermodynamic simulations, X-ray diffraction (XRD), scanning electron microscopy (SEM) characterizations, and EIS results. This proposed mechanism confirms that a slurry aluminide coating is able to improve the stainless steel behavior in molten carbonate. However, the TA6V titanium alloy is the most resistant material in molten carbonate but the Al-coated stainless steels appear as the best lifetime-cost compromise.Publicación Restringido Anomalous steam oxidation behavior of a creep resistant martensitic 9 wt. % Cr steel(Elsevier, 2013-06-09) Agüero, Alina; González, Vanessa; Mayr, Peter; Spiradek Hahn, Krystina; Ministerio de Economía y Competitividad (MINECO)The efficiency of thermal power plants is currently limited by the long-term creep strength and the steam oxidation resistance of the commercially available ferritic/martensitic steel grades. Higher operating pressures and temperatures are essential to increase efficiency but impose important requirements on the materials, from both the mechanical and chemical stability perspective. It has been shown that in general, a Cr wt. % higher than 9 is required for acceptable oxidation rates at 650 °C, but on the other hand such high Cr content is detrimental to the creep strength. Surprisingly, preliminary studies of an experimental 9 wt. % Cr martensitic steel, exhibited very low oxidation rates under flowing steam at 650 °C for exposure times exceeding 20,000 h. A metallographic investigation at different time intervals has been carried out. Moreover, scanning transmission electron microscopy (STEM) analysis of a ground sample exposed to steam for 10,000 h at 650 °C revealed the formation of a complex tri-layered protective oxide comprising a top and bottom Fe and Cr rich spinel layer with a magnetite intermediate layer on top of a very fine grained zone.Publicación Restringido Effects of a Steam Pre-treatment on the Formation and Transformation of Alumina Phases on Fe Aluminide Coatings(Springer Nature Link, 2012-12-25) Agüero, Alina; Hernández, M.; Santaballa, A.; Ministerio de Economía y Competitividad (MINECO)Several researchers have studied the transformation of metastable aluminas (γ- and θ-) to α-Al2O3 but very little is known regarding alumina scales formed under water vapour and their transformation to α-Al2O3. Some results have indicated that water vapour increases the oxidation rate of alumina-scale forming coatings but others have found the opposite, that is, that under water vapour the oxidation rates decrease as either transition aluminas do not form or the transformation to α-Al2O3 is accelerated. In addition, it was found that χ-Al2O3 is the only oxide that forms at the initial stages of oxidation under 100 % steam on Fe–Al coatings at 650 °C. Under these conditions, this oxide is very protective, and slowly transforms onto α-Al2O3. A preliminary study of the transformation of χ- to α-Al2O3 at 900 °C under laboratory air was carried out. χ-Al2O3 was generated by a steam pre-treatment on slurry Fe aluminide coatings deposited on P92.Publicación Acceso Abierto Recubrimientos protectores para componentes de turbinas de aviación y de generación de energía depositados por proyección por plasma(Elservier, 2000-07-26) Agüero, Alina; Álvarez Alba, J.; García de Blas, Javier; Valles González, M. P.Coatings produced by aluminium diffusion, called aluminide are employed to increase the oxidation and corrosion resistance, increasing the life of Ni and Co base superalloys components at temperatures comprised between 900 and 1050ºC. Consequently these coatings are frequently employed in aeronautic and power generation turbines as well as in the chemical industry. Aluminides are industrially produced by pack cementation or CVD and recently it has been demonstrated that its resistance significantly increases when Cr is added (chrome-aluminides). During this work, a feasibility study has been carried out in order to determine if plasma spray can be employed for depositing this type of coatings on turbine blades. Therefore, aluminium and aluminium/chromium layers were deposited on Ni base IN100 superalloy specimens that were subsequently subjected to a diffusion heat treatment under Ar flow. Characterisation and analysis of the coatings were carried out by metallography , SEM and EDS. Cyclic oxidation tests were carried out at 1050º C while molten sulphate hot corrosion was performed at 900º C. The results of this preliminary study are promising and indicate that plasma spray can be developed as an industrial process for production of aluminide and chrome-aluminide coatings.
Los recubrimientos producidos por difusión de aluminio, llamados aluminuros, se emplean para aumentar la resistencia a la oxidación y a la corrosión, incrementando la vida de componentes fabricados con superaleaciones de níquel y cobalto a temperaturas comprendidas entre 900 y 1050º C. Por ello se emplean muy frecuentemente en turbinas aeronaúticas y de producción de energía y en la industria química. Los aluminuros se obtienen industrialmente mediante cementación o CVD y recientemente se ha demostrado que su resistencia aumenta significativamente cuando se añade cromo (cromoaluminuros). Durante el presente trabajo, se ha realizado un estudio de viabilidad para determinar si la proyección por plasma puede ser utilizada para la producción de estos recubrimientos sobre álabes de turbina. Así pues, se depositaron capas de aluminio y aluminio/cromo sobre probetas de la superaleción base níquel IN100 que a continuación fueron sometidas a un tratamiento térmico de difusión bajo flujo de argón. La caracterización y análisis de los recubrimientos producidos se llevó a cabo mediante técnicas metalográficas, microscopía electrónica de barrido y espectroscopía de dispersión de energía de rayos X. Se realizaron ensayos de oxidación cíclica a 1050ºC y de corrosión por sulfatos fundidos a 900ºC. Los resultados de este estudio preliminar han sido muy satisfactorios e indican que la proyección por plasma puede ser desarrollada como procedimiento industrial para la producción de recubrimientos aluminuros y cromoaluminuros.Publicación Acceso Abierto Aluminide Coatings by Means of Slurry Application: A Low Cost, Versatile and Simple Technology(MPDI, 2024-09-29) Agüero, Alina; Audigié, Pauline; Lorente Sánchez, Cristina; Gutiérrez del Olmo, Marcos; Mora, Julio; Sergio, Rodríguez Catela; European Commission; Agencia Estatal de Investigación (España)The present study focused on demonstrating the versatility of the slurry deposition technique to produce aluminide coatings to protect components from high-temperature corrosion in a broad temperature range, from 400 to 1400 °C. This is a simpler and low-cost coating technology used as an alternative to CVD and pack cementation, which also allows the coating of complex geometries and offers improved and simple repairability for a lot of industrial applications, along with avoiding the use of non-hazardous components. Slurry aluminide coatings from a proprietary water-based-Cr6+ free slurry were produced onto four different substrates: A516 carbon steel, 310H AC austenitic steel, Ti6246 Ti-based alloy and TZM, a Mo-based alloy. The resulting coatings were thoroughly characterised by FESEM and XRD, mainly so that the identification of microstructures and appropriate phases was reported for each coating. The importance of surface preparation and heat treatment as key parameters for the coating final microstructures was also evidenced, and how those parameters can be optimised to obtain stable intermetallic phases rich in Al to sustain the formation of a protective Al2O3 oxide scale. These coating systems have applications in diverse industrial environments in which high-temperature corrosion limits the lifetime of the components.
