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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Raúl
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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 HVOF-Deposited WCCoCr as Replacement for Hard Cr in Landing Gear Actuators(Springer Nature Link, 2011-10-05) Agüero, Alina; Camón, F.; García de Blas, Javier; del Hoyo Gordillo, Juan Carlos; Muelas Gamo, Raúl; Santaballa, A.; Ulargui, S.; Vallés, P.WCCoCr coatings deposited by HVOF can replace hard Cr on landing gear components. Powders with two different WC particle sizes (micro and nano-) and geometries have been employed to study the effects on the coating’s properties. Moreover, coatings produced employing two sets of parameters resulting in high and low flame temperatures have been evaluated. Minor differences in microstructure and morphology were observed for the two powders employing the same spraying parameters, but the nano-sized powder exhibited a higher spraying efficiency. However, more significant microstructural changes result when the low- and high-energy spray parameters are used. Moreover, results of various tests which include adhesion, wear, salt fog corrosion resistance, liquid immersion, and axial fatigue strength, indicate that the coatings produced with high-energy flame are similar in behavior. On the other hand, the nanostructured low-energy flame coating exhibited a significantly lower salt fog corrosion resistance.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.Publicación Restringido Performance of HIPIMS deposited CrN/NbN nanostructured coatings exposed to 650 °C in pure steam environment(Elsevier, 2016-05-20) Hovsepian, P.; Ehiasarian, A. P.; Purandare, Y. P.; Biswas, B.; Pérez, F. J.; Lasanta, M. I.; De Miguel, M. T.; Illana, A.; Juez Lorenzo, M.; Muelas Gamo, Raúl; Agüero, AlinaIn the current work, 4 μm thick CrN/NbN coating utilising nanoscale multilayer structure with bi-layer thickness of Δ = 2.9 nm has been used to protect 9 wt% Cr steels such as P92 widely used in steam power plants. The uniquely layered coatings have a combination of nitrides of chromium and niobium which are not only resistant to aqueous corrosion and corrosion-erosion and have excellent tribological properties, but also have oxidation resistance in dry air up to a temperature of 850 °C. The novel High Power Impulse Magnetron Sputtering (HIPIMS) deposition technology has been used to deposit CrN/NbN with enhanced adhesion (critical load of scratch adhesion LC2 = 80 N) and a very dense microstructure as demonstrated by Transmission Electron Microscopy (TEM) imaging. These superior coating properties are achieved due to the unique high metal ion content (up to 90%) in the HIPIMS plasma, which allows particle acceleration and trajectory control by external electrical and magnetic fields thus delivering highly energetic material flux on the condensing surface. P92 bare and coated samples were oxidised at 650 °C in 100% steam atmosphere up to 2000 h, in order to simulate the future operation conditions of steam turbines employed in power plants. The oxidation kinetics was evaluated by mass gain measurements. Under these conditions CrN/NbN provided reliable protection of the P92 steel. The paper also discusses the effect of growth defects and high temperature crack formation analysed by Scanning Electron Microscopy and Focused Ion Beam-Scanning Electron Microscopy techniques (SEM and FIB-SEM, respectively) on the high temperature corrosion resistance in pure steam atmosphere thus revealing the coatings potential failure mechanisms.Publicación Restringido Laboratory corrosion testing of coatings and substrates simulating coal combustion under a low NOx burner atmosphere(Wiley online library, 2013-07-02) Agüero, Alina; Gutiérrez del Olmo, Marcos; Muelas Gamo, Raúl; Plana, Daniel; Román, A.; Hernández, M.It is certainly a difficult task to evaluate new materials and coatings to be used for boilers in power plants, as conditions are extremely complex, comprising a highly erosive environment, high temperature, highly corrosive gases, and reactive deposits. In particular, early catastrophic failures, as well as higher degradation rates have been observed on different power plant boiler components when operating under atmospheres containing low levels of oxygen. These atmospheres are typical of low NOx burners, and can be more corrosive than normal oxidizing conditions. The presence of a sulfidizing atmosphere as well as ash deposits present in boilers, are in part responsible of this accelerated damage. In this work, testing under a low oxygen atmosphere has been carried out on T22 and P92 uncoated and coated specimens. The atmosphere was equal to that measured in a Spanish coal-fired power plant (ENDESA, Compostilla, León) and the test temperature was 580 °C. Tested coatings were slurry applied aluminides, as well as two HVOF sprayed coatings including a commercially deposited Cr2C3NiCr, and a newly developed Cr2O3-Cr composite coating. The specimens were covered with ash (taken from the plant) prior to testing. After testing, the uncoated substrates exhibited high thickness oxides with some sulfide inclusions whereas all tested coatings were very protective. Exposed samples of T22 tubes employed in the Compostilla power plants were analyzed and compared with the corresponding specimens tested in the laboratory. In both cases, the scales contained Fe3O4 and FeS but the sulfide content was significantly higher in the scale formed in the plant. Moreover, ash particles were found embedded in the both scales.Publicación Restringido Vacuum tribological behaviour of self-lubricating quasicrystalline composite coatings(Wiley, 2006-03-09) García de Blas, Javier; Román, A.; De Miguel, C.; Longo, Federico; Muelas Gamo, Raúl; Agüero, AlinaHigh-temperature-resistant self-lubricating coatings are needed in space vehicles for components that operate at high temperatures and/or under vacuum. Thick composite lubricant coatings containing quasicrystalline alloys as the hard phase for wear resistance can be deposited by a thermal spray technique. The coatings also contain lubricating materials (silver and BaF2CaF2 eutectic) and NiCr as the tough component. This paper describes the vacuum tribological properties of TH103, a coating of this type, with a very good microstructural quality. The coating was deposited by high-velocity oxygen fuel spraying and tested under vacuum using a pin-on-disc tribometer. Different loads, linear speeds, and pin materials were studied. The pin scars and disc wear tracks were characterised using a combination of scanning electron microscopy and energy dispersive spectrometry. A minimum mean steady friction coefficient of 0.32 was obtained when employing an X750 Ni superalloy pin in vacuum conditions under 10 N load and 15 cm/s linear speed, showing moderate wear of the disc and low wear of the pin.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 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.Publicación Restringido Corrosion Resistance of Novel Coatings on Ferritic Steels for Oxycombustion–Supercritical Steam Boilers: Preliminary Results(Springer Nature Link, 2015-07-23) Agüero, Alina; Baraibar, Ignacio; González, Vanessa; Muelas Gamo, Raúl; Plana, Daniel; European Commission; Ministerio de Economía y Competitividad (MINECO)Increasing the efficiency of coal fired steam power plants is an important contribution towards clean coal power. In fact, new ferritic steels are expected to withstand 325 bar and 650 °C. Moreover, in order to facilitate CO2 capture oxygen can be used instead of air for combustion (oxycombustion) so that no NOX emissions are produced. Boiler components, such as superheater tubes, are exposed to both steam and fireside corrosion and at higher temperatures, ferritic steels corrode at very fast rates under both atmospheres. A solution can be found in the use of protective coatings, a number of which, applied by techniques capable of depositing said coatings both on the inner and outer surfaces of tubes, are being studied within nationally and European funded projects. In particular, two new Ni and Cr modified aluminide coatings deposited on P92 by non-line-of-sight hybrid processes have been produced and the preliminary results of on-going laboratory testing, both under oxycombustion model atmospheres as well as under pure steam at 650 °C are promising, in particular those exhibited by the Cr enriched aluminide coating. Moreover, results obtained in a pilot oxycombustion boiler operated by CIUDEN in Leon, Spain are also shown.
