The effect of the deposition sequence of sol-gel SiO2-Al2O3, CeO2 and Y2O3 coatings on the corrosion resistance of the FeCrAl alloy during cyclic high-temperature oxidation

The surface of a ferritic FeCrAl alloy was covered with three-layer ceramic coatings by the sol-gel method. The SiO2-Al2O3, Y2O3 and CeO2 layers would be deposited in different sequences. The obtained material would be subjected to cyclic oxidation at a temperature of 900 degrees C. It was found that the sequence in which the layers are deposited affects the morphology and chemical composition of the scale. After 20 oxidation cycles (each lasting 12 h) the thickness of the building up oxide film amounted to 2.3-4.2 mu m. Gravimetric analyses showed the parabolic character of the weight gain-oxidation time interdependence. The first layer deposited on the metallic surface determines the distribution of yttrium and cerium in the scale and in the alloy core. The scale building up on the samples in which yttrium oxide formed the first layer was found to have the most advantageous protective properties. After 20 oxidation cycles the FeCrAl alloy coated in turn with the layers: Y2O3, CeO2 and SiO2-Al2O3 showed the smallest relative change in weight. In comparison with the uncoated substrate the protection effectiveness of the deposited coatings amounts to 12-37%.