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 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 Low temperature MOCVD process for fast aluminium deposition on metallic substrates(Wiley, 2005-12-19) Agüero, Alina; Gutiérrez del Olmo, Marcos; García-Martínez, MaríaA CVD pilot plant, designed and built in INTA, is presently being used to deposit aluminium coatings with applications in the fields of industrial and aeronautic turbines, as well as on the protection of components employed in the chemical industry, waste incinerators, fuel cells, and for the replacement of Cd coatings in aeronautic components. The industrial process currently used to coat aeronautic and industrial turbine components employs AlCl3 as precursor at 700–1100 °C and requires more than 12 h per batch (including loading, heating, coating and cooling) due to the relatively low deposition rates and the long heating and cooling cycles. The new process carried out at INTA employs an organometallic precursor, which results in higher deposition rates, at 280–350 °C with a total processing time lower than 5 h per batch. As in any other CVD process, this one allows deposition of coatings in complex geometry components such as on the inner surfaces of turbine blades and heat exchangers tubes. Other important advantages of this particular process are the possibility of recovering and re-utilising the unreacted precursor as well as the high purity of the produced coatings in comparison with those produced by other commercially available technologies. It is well known that the higher the contamination degree, the lower the useful life of this type of coatings. The pilot plant has a deposition chamber with a useful coating zone of 30 cm in length and 18 cm in diameter, heated by a three zone furnace equipped with a pumping system that allows working pressures of 0.1–100 mbar. The system can be manually or automatically controlled and can be easily adapted to deposit other materials. By heat treating the pure Al coatings deposited on Ni base superalloys, Ni aluminide coatings have been obtained and excellent cyclic oxidation behaviour has been observed at 1000 °C. Al has also been deposited on ferritic steels (P91 and 92) and after a suitable heat treatment Fe aluminide coatings with excellent steam oxidation resistance have been obtained. Another potential important use of this process is the deposition of dense aluminium coatings for cadmium replacement in several industrial applications.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; Rodríguez Catela, Sergio; 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.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 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 Oxidation under pure steam: Cr based protective oxides and coatings(Elsevier, 2013-09-20) Agüero, Alina; González, Vanessa; Gutiérrez del Olmo, Marcos; Muelas Gamo, RaúlAt temperatures of 900 °C and higher, the formation, transformation and failure of protective oxides in air have been deeply studied. However, 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 625–700 °C, at which the candidate ferritic/martensitic steels exhibit very low steam oxidation resistance. In this paper, available knowledge of the behavior of Cr based protective oxides formed under steam at 650 °C will be presented. It is already known that on ferritic/martensitic steels with a Cr content lower than ~ 9 wt.% such as P92, a nonprotective, thick, dual layer composed of Fe3O4 and (Fe, Cr)3O4 forms. However, significantly higher steam oxidation resistance has been recently found when exposing NPM, a 9 wt.% Cr martensitic steel rich in W and Co, to pure steam at 650 °C. In this case a protective, very thin multilayer forms, with alternating Fe3O4 and (Fe, Cr, Mn)3O4 layers. Different oxides formed after 10,000 h of exposure to steam at 650 °C, on Cr containing coatings. In the case of Fe based, Cr rich coatings, both diffusion and overlay, a protective spinel was observed. However, Cr containing coatings based on Ni develop a very stable, protective thin Cr2O3 layer. Results show that along with the Cr content, other factors such as the grain size below the scale appear to determine the formation of thin protective scales. The steam pressure was also found to significantly and negatively affect the stability of protective Cr based oxides. Chromia former steels and coatings may not be the best solution for 650 °C new generation steam power plants.
