Examinando por Autor "Gutiérrez, Marcos"

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Restringido
Cyclic Oxidation of Steam Pre-oxidized MCrAlY and Ni Aluminide Coatings
(Turbine Forum, 2004-08-25) Agüero, A.; Román Gárate, Alicia; Gutiérrez, Marcos
Significant attention has been paid to high temperature oxidation resistant coatings such as overlay MCrAlYs and diffusion Ni aluminide coatings to protect superalloys in both aeronautic and gas turbine components. Both coatings behave as Al reservoirs in order to form a protective Al2O3 layer. Said layer is very stable but grows with exposure time and will also tend to spall due to thermal cycling. Both types of coatings are also employed as bond layers for thermal barrier ceramic coatings (TBCs), which are employed to maintain a lower surface temperature for refrigerated turbine components. The bond coating has a dual function as it reduces the thermal expansion coefficient mismatch between the ceramic layer and the superalloy, and protects the superalloy from environmental degradation due to air as well as other contaminants that will permeate through the porous ceramic top layer. The main cause of failure of TBCs is related to spalling of the ceramic top layer due to stresses resulting from the Al2O3 growth at the bond coating-thermal barrier interface. It has been shown that bond coat pre-treatment prior to the TBC deposition has a strong influence on the oxidation resistance of these coatings. Moreover, recent results by C. Zhou and collaborators have indicated that steam present in air will significantly increase the oxidation rate of TBCs (with MCrAlYs as bond coating) and the cause is attributed to the formation of thick porous mixed oxides related to the presence of steam. The authors suggest that H dissolved into the initially formed oxides enhance Ni and Cr ion outwards diffusion.
Acceso Abierto
Latest Results in the Development of Steam Resistant Coatings for New Generation High Temperature Supercritical Steam Plants
(Turbine Forum, 2006-03-12) Agüero, A.; Muelas Gamo, Raúl; Gutiérrez, Marcos
Restringido
Low temperature MOCVD process for fast aluminium deposition on metallic substrates
(Wiley, 2005-12-19) Agüero, A.; Gutiérrez, Marcos; García Martínez, María
A 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.
Acceso Abierto
Thermal cyclic resistance and long term inter-diffusion properties of slurry aluminide coatings modified with Si
(Elsevier, 2022-02-15) Agüero, A.; Landeira Ostergard, M. J.; Hansson, A. N.; Gutierrez, Marcos; Instituto Nacional de Técnica Aeroespacial (INTA)
High temperature oxidation resistant aluminide coatings fail due to their inability to maintain a protective scale. The corresponding mechanism of protection is based on of forming a thin Al2O3 layer, which depends on the availability of Al at the interface with the intermetallic coating. However, the Al content in the coating’s surface decreases with time at high temperatures due to interdiffusion with the substrate and/or frequent regeneration of the protective Al2O3 scale when it spalls. Si addition is known to enhance the life of Ni aluminide coatings under certain corrosion environments. In an effort to develop a stable, long lasting coating for industrial components exposed to metal dusting, diffusion aluminide coating has been produced by applying Al-Si slurries of various compositions on alloy 601. Aluminide coatings were prepared by applying a water base, Al slurry to which 1, 10 and 20 wt. % of Si were added, followed by a diffusion heat treatment. The microstructures of the coatings were similar, exhibiting an outer layer consisting of an Al-rich -NiAl matrix, an almost stoichiometric -NiAl inner layer and an interdiffusion zone between the coating and the alloy. Thermal cyclic tests in air at 1100 °C have demonstrated good adhesion and stability of all coatings. In addition, long term isothermal tests at 850 °C for up to 3 months in air showed high oxidation resistance of the coating but different degree of coating degradation depending on the composition. The coating with the lowest Si addition was the most stable.