Abstract
Thermally grown oxide (TGO) scales can provide high temperature oxidation protection if they are slow growing, sound and adherent to the substrate. In thermal barrier coatings (TBCs), failure occurs near or at the interface between the metallic bondcoat and its thermally grown alumina layer. Oxide scales consisting mainly of alumina were grown on duplex (ZrO 2/bondcoat) and functionally graded (ZrO 2/Al 2O 3/bondcoat) systems through static heat treatment at 1050 °C. Electron microscopy was used to analyze the microstructures of oxide layers grown on various TBC systems. The difference in thickness of grown oxide scale that resulted from oxidation of various TBC systems was discussed in the light of the effectiveness of alumina interlayer functioning as an additional oxidation barrier. Spallation observed at higher temperature in a functionally graded system was due to phase transformation of γ-Al 2O 3 to α-Al 2O 3, inducing additional residual stress causing a premature failure. However, TBC systems with a thin layer of Al 2O 3 were found to be effective in improving oxidation resistance of protective coatings.
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