Browsing by Keyword "High temperature corrosion"
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Item High-temperature oxidation of CrAlYN coatings: Implications of the presence of Y and type of steel(2018-11-25) Rojas, T. C.; Domínguez-Meister, S.; Brizuela, M.; Sánchez-López, J. C.; INGENIERÍA DE SUPERFICIESNanolayered CrAlN and CrAlYN/CrAlN (average contents of Al ≈ 25 at.% and Y ≈ 1.6 at. %) coatings are deposited on M2 and 316 steel substrates and heated to 1000 °C in air for 2 h to study their oxidation mechanism, the thermal stability and the reactive element (RE) effect of yttrium. CrAlN on M2 develops a Cr2O3/Al2O3 passivation layer that preserves in high degree the fcc-CrAlN structure however iron ions leave the substrate and travel to the surface along the column boundaries. The CrAlYN/CrAlN coatings deposited on steels are not stable at 1000 °C, and the initial fcc-CrAlN phase is partially transformed to hcp-Al(O)N and Cr-Fe phases (M2) and Cr2N and Al2O3 (316). The addition of Y changes the predominant scale growth direction. Inward oxygen diffusion becomes dominant but a reduction of the oxide scale thickness as compared to CrAlN is not observed. The advanced microstructural analysis made by transmission electron microscopy combined with electron energy-loss spectroscopy determined that yttrium migrates mainly to the oxide scale (forming mixed oxides with substrate elements - V and Mo, either as dispersed particles or segregated at the grain boundaries) in M2, and to the oxide interface and column boundaries (forming Al-Y oxides and YN, respectively) in 316 steel. The benefits of addition of Y in improving the oxidation resistance are discussed comparatively with literature data. The RE effect of yttrium is thus observed to be dependent on the substrate, film architecture and composition.Item Influence of Al and Y content on the oxidation resistance of CrAlYN protective coatings for high temperature applications: New insights about the Y role(2019-01-30) Rojas, T. C.; Domínguez-Meister, S.; Brizuela, M.; Sánchez-López, J. C.; INGENIERÍA DE SUPERFICIESCrAlYN hard coatings with two different average Al contents: ∼16 at.% and ∼25 at.%, and Y concentration varying between 1.2 and 5.7 at.% were deposited by direct current reactive magnetron co-sputtering of mixed Cr-Al and Y targets on commercial M2 steel substrates. The samples were heated to 1000 °C in air during 2 h to study their oxidation resistance and thermal stability. The Y content is critical and the coatings present different behaviour depending on the Al content. The best oxidation resistance and thermal stability are obtained for the coating with ∼16 at.% Al and 3.4 at.% Y. The initial film microstructure and the cubic phase (fcc-CrAlN) were retained, and a thin (Cr,Al)2O3 oxide protective scale was formed. At lower Y content (1.2 at.%) iron, from the substrate crosses the coating, while a higher content (4.6 at.%) avoided the iron diffusion at the expense of a thicker oxide scale with new oxide phases. The coatings with higher Al content (∼25 at. %) were not thermally stable at 1000 °C. A good oxidation resistance was obtained for 2.6 at.% of Y although new phases (hcp-AlN and Cr-Fe) were formed. Higher amount of yttrium (∼5.7 at. %) led to the complete oxidation of the coating.