Modified thick thermal barrier coatings: microstructural characterization

Thick thermal barrier coatings were modified with laser glazing and phosphate based sealing treatments. Surface porosity of the sealed coatings decreased significantly in all cases. Structural analysis showed a strong preferred crystal orientation of the t′ZrO2 phase in direction [002] in laser-glazed 25CeO2–2.5Y2O3–ZrO2 coating. In laser-glazed 22MgO–ZrO2 coating the major phase was rhombohedral Mg2Zr5O12. In phosphate sealed 8Y2O3–ZrO2 coating the strengthening mechanism was identified as adhesive binding without chemical bonding. Coating microstructures were determined by scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy and optical microscopy. Coatings were also characterized by X-ray diffraction, microhardness and porosity.