Colombia. Students from Universidad del Valle conducted research related to the evaluation of multilayer coatings of α-Al2O3 /8YSZ for protection against corrosion at high temperatures.
The objective of this research project is the synthesis and characterization of thermal barrier coatings (TBC – thermal barrier coatings, for its acronym in English) multilayer type of α-Al2O3 / 8YSZ in the form of a thin film, for their applications in high performance devices, such as those that are deposited on metal alloys subjected to high temperatures.
The project includes synthesis, growth, characterization, in particular its behavior to corrosion at high temperatures. Coatings with a multilayer structure are one of the most effective current proposals to achieve coatings with improved properties. This type of systems or structures are based on the periodic stacking of alternating layers of different materials, so these structures improve the adhesion of the coating to the substrate, by reducing internal stresses and the fragility of the material.
In the research, multilayer coatings of alumina in alpha phase (α-Al2O3) were deposited, which is a stable oxide of slow growth and with a moderate coefficient of thermal expansion and Zirconia stabilized with Yttria at 8% (8YSZ) coating used in tribological applications at high temperatures due to its low thermal conductivity, high coefficient of thermal expansion, (similar to that of metals), good combination of high toughness, relatively high hardness and resistance to erosion corrosion.
The substrates used were high-temperature steels and silicon for certain types of characterizations. In order to study the influence of period variation in this type of coatings, on its crystal structure, and the possible change in the properties of corrosion resistance at high temperatures, it is proposed to design multilayers of [α-Al2O3/8YSZ]n varying the number of bilayers in 1, 10, 30, 50 and 70 and the spatial periodicity in λ = 1.5 μm, λ = 300 nm, λ = 100 nm, λ = 60 nm, λ = 43 nm, keeping the total film thickness constant at 2 μm. The samples will be characterized structurally and morphologically by X-ray Diffraction (XRD), Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The study of electrochemical behavior at high temperatures will be carried out by means of the corrosion test by molten salts by means of Electrochemical Impedance Spectroscopy (EIS).
The main academic impact, as a result of the studies of the behavior before thermal cycling and corrosion at high temperatures carried out with the multilayers of [8YSZ/α-Al2O3]n deposited by cathodic spraying, is that due to their nanostructural characteristics, these multilayers present a performance similar to those of the commercial thermal barrier micrometric coatings deposited by conventional techniques. This opens up a possibility of the application of this type of multilayer nanostructured coatings of [8YSZ/α-Al2O3]n in high-performance devices, such as those that are deposited on metal alloys subjected to high temperatures.
The authors of this study were Gustavo Zambrano Romero, María Gómez, Yesid Aguilar Castro, César Amaya, Óscar Sánchez, Nathalia Díaz, Andrés Escarraga, Melisa Burgos and Mario Millán.
Find the results of the research by clicking here.
Source: Universidad del Valle.
