Examinando por Autor "Gutiérrez, Marcos"

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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
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.