Persona: Audigié, Pauline
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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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Pauline
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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 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.Publicación Acceso Abierto Modified high hardness steel coating for biomass corrosion protection(Springer Nature Link, 2025-09-13) Agüero, Alina; Gutiérrez del Olmo, Marcos; Audigié, Pauline; Sergio, Rodríguez Catela; Pascual Ferreiro, JonBiomass is a renewable and CO2-neutral energy source. However, the efficiency of biomass combustion plants remains lower than that of current fossil fuel-based systems. To minimize corrosion from aggressive species found in biomass combustion, these plants currently operate at a maximum temperature of 550 °C. The European project BELENUS explored new materials and coatings to raise the operating temperature to 600 °C, thereby improving plant efficiency. Among the coatings under investigation, a super high-hardness steel (SHS) modified with Al, applied by high velocity oxy-fuel (HVOF) thermal spray on ferritic steel SVM12, has demonstrated an improved performance in the laboratory, exposed to a model biomass environment containing KCl deposits for 8000 h at 600 °C. Microstructural analysis by field emission scanning electron microscopy (FESEM) and X-ray diffraction was conducted on the tested samples to examine the coating’s evolution in these environments, as well as the associated protection and degradation mechanisms. The presence of Al within the coating significantly enhanced its resistance to biomass corrosion when compared to uncoated SVM12 and the Al-free SHS coating. Possible reasons for the improved behaviour of the Al-modified coating are the reduction of porosity as well as the blocking effect of either intermetallic FeAl or Al oxide which forms at the splat boundaries prior to exposure to the corrosive atmosphere.Publicación Acceso Abierto 10,000 h molten salt corrosion testing on IN617, uncoated and aluminide ferritic steels at 580 ºC(Richter C., 2020-12) Agüero, Alina; Audigié, Pauline; Sergio, Rodríguez Catela; European Commission (EC)Long term testing of two ferritic-martensitic steels (P91 and VM12-SHC) with and without slurry deposited aluminide coatings containing 20 wt.% of Al at the surface was carried out by exposing these materials to the Solar Salt, a eutectic mixture composed of 60 % NaNO3 - 40 % KNO3 at 580ºC. This salt is currently used in operating thermal solar power plants as heat transfer and storage fluid. Tubes made of expensive Ni based alloys are employed to mitigate corrosion. The tested uncoated ferritic materials exhibited very high corrosion rates developing thick, easily detached scales. IN617 was also tested as a reference and experienced very low corrosion up to 5,000 h, but after 10,000 h a 50 ȝm thick, mostly NiO scale had developed with Na0.6CoO2 crystals deposited on top. There was also evidence of significant Cr depletion at the alloy surface. Carcinogenic CrVI was found in the Solar Salt melt in which the three uncoated alloys were immersed. In contrast, the two coated ferritic steels did not show evidence of degradation after 10,000 h and the most significant microstructural change was the development of a very thin protective NaAlO2 layer on their surface. An industrial process to deposit these coatings on the inner surfaces of pipes has already been developed.Publicación Restringido Comparison of descaling methods to study the corrosion kinetics of ferritic steels after dynamic exposure to molten carbonates(Elsevier, 2022-12-24) Audigié, Pauline; Sergio, Rodríguez Catela; Agüero, Alina; Pedrosa, Fátima; Paiva, Teresa; Diamantino, Teresa C.T91 ferritic-martensitic steel was exposed to Li, Na and K molten carbonates at 650ºC under dynamic conditions up to 1000 h. After testing, three descaling methods, two from the ISO8407 and one from the ISO17245 standards were applied to remove the corrosion products and determine the corrosion rates. The two ISO8407 methods were more appropriate although the procedure required several steps to fully remove the corrosion products. The ISO17245 method led to a higher mass loss affecting probably the base material. Oxides identification was performed by XRD following step by step layers removal. Li-, Na-, K-containing oxides and chromates/chromites were detected.Publicación Restringido Analysis of void formation in Pt-rich γ-γ’ bond-coatings for TBC system application(Elsevier, 2025-02-21) Audigié, Pauline; Vande Put, Aurélie; Malard, Benoit; Malié, André; Monceau, DanielPt-rich γ-γ’ bond-coatings for thermal barrier coating systems may lead to detrimental pore formation. An extensive analysis of literature on voids nucleation and growth in the different metallic components of several kinds of TBC systems was performed. The study then focused on Pt-rich γ-γ’ bond-coating/Ni-based superalloy systems employing an original statistical analysis of voids formation and spatial distribution through secondary electron microscopy with focused ion beam sequential cross sectioning and synchrotron X-Ray tomography. It was found that pores at the Pt-rich γ-γ’ bond-coating/superalloy interface form due to the Kirkendall effect, with the highest concentration located at the Pt diffusion front.Publicación Restringido Performance study of slurry aluminide coated 347H immersed in Li-Na-K carbonate molten salt for 5000-h at 700 °C(Elsevier, 2025-10-06) Oger, Loïc; Agüero, Alina; Audigié, Pauline; European CommissionConcentrated Solar Power (CSP) systems coupled with thermal energy storage (TES) are increasingly considered to provide dispatchable, low-carbon energy. To further improve their performance, next-generation CSP plants are designed to operate under more severe conditions, which raises concerns regarding high-temperature corrosion of structural materials by molten salts. This study examines the corrosion behaviour of bare and slurry aluminide-coated 347H stainless steel after exposure to a Li–Na–K carbonate eutectic at 700 °C for up to 5000 h. The uncoated alloy showed rapid degradation, characterized by a brittle, multi-layered oxide scale, extensive internal oxidation, and carburization. The outer oxide layer consisted mainly of LiFeO₂ and LiMnO₂, while the internal oxidation zone contained (Fe,Cr)₃O₄ spinels, LiCrO₂, and Ni-rich metallic islands. In contrast, the aluminide-coated samples exhibited excellent corrosion resistance without spallation or mechanical failure. The coating transformed into a compact FeAl layer, overlaid by a dense oxide composed of α- and γ-LiAlO₂. The α-LiAlO₂ phase, forming at the oxide–coating interface via the reaction of Al₂O₃ with lithium oxide, acted as a continuous and chemically stable barrier. Its persistence during exposure was key to prevent molten salt ingress and ensure long-term protection. These findings demonstrate that slurry aluminide coatings effectively increase the durability of structural alloys in molten carbonate environments relevant for advanced CSP-TES applications.Publicación Restringido High temperature corrosion beneath carbonate melts of aluminide coatings for CSP application(Elsevier, 2020-03-20) Audigié, Pauline; Encinas Sánchez, V.; Sergio, Rodríguez Catela; Pérez Trujillo, Francisco Javier; Agüero, Alina; European CommissionSlurry iron-aluminide coatings deposited by spraying on 9 wt% Cr P91 alloy as well as uncoated P91 were exposed isothermally at 650 °C to a ternary molten salt mixture based on a Na, K and Li carbonate eutectic, under static and dynamic conditions. Uncoated P91 evidenced considerable mass gains and extensive spallation in both conditions. Indeed, P91 developed a very thick fast growing multilayered oxide scale which included LiFeO2, LiFe5O8 and (Fe,Cr)3O4. Under dynamic conditions, the metal loss was higher that when the test was carried out statically but this was not reflected in the gravimetric measurements likely due to spallation of the scales in both cases. The coated systems performed better than the uncoated material up to at least 1000 h according to metallographic inspection. However, the aluminide coating showed non-uniform attack and on the corresponding zones, a thick layer likely consisting of LiFeO2 developed over an internal oxidation zone corresponding to all of the coating initial thickness. K was also detected within the internal oxidation zone suggesting that the coating was internally attacked at least by K containing species (Li cannot be detected by EDS). K and perhaps Li seem to diffuse along the grain boundaries of the coating, leading to internal oxidation responsible for the degradation. On the non-degraded zones, the coating maintained the initial microstructure as very low coating/substrate interdiffusion occurred. A 20 wt% average Al content at the surface does not seem to be high enough to sustain a protective oxide.
