Modified thick thermal barrier coatings: Thermophysical characterization

Thermophysical properties of modified zirconia based thick thermal barrier coatings (8Y2O3–ZrO2, 25CeO2–2.5Y2O3–ZrO2 and 22MgO–ZrO2) were characterized at temperature range of RT-1300 °C. Coatings were studied in laser-glazed and phosphate sealed state, and their properties were compared to as-sprayed coatings. Laser glazing affected only slightly on thermal conductivity of the studied coatings. If the segmentation cracks, induced by laser glazing, were oriented vertically like in the case of laser-glazed 8Y2O3–ZrO2 coating, thermal conductivity was increased in some degree. But if the orientation of the segmentation cracks was deviated from the vertical direction or if the cracks were branched, thermal conductivity was decreased. This was the case with the laser-glazed 25CeO2–2.5Y2O3–ZrO2 and 22MgO–ZrO2 coatings. Phosphate based sealing treatments were found to increase the thermal conductivity of all coatings. Aluminium phosphate sealing also lowered the high temperature stability of the 8Y2O3–ZrO2 coating down to 1000 °C. In 8Y2O3–ZrO2 and 25CeO2–2.5Y2O3–ZrO2 based coatings thermal conductivity was increased in consecutive measurement cycles, caused mainly by the sintering based phenomena in which the contact between overlapping lamellae was improved. Thermal conductivity of the 22MgO–ZrO2 based coatings was increased significantly in the first measurement cycle because of the unstabilization of zirconia-caused by precipitation of MgO.