Changes in high-temperature thermal properties of modified YSZ with various rare earth doping elements

Abstract

To protect the high-temperature components of gas turbines, 6-8 wt.% yttria stabilised zirconia (YSZ) has been extensively used as a thermal barrier coating (TBC) material. However, its application is severely limited at high temperatures because of zirconia phase transition and sintering densification above 1200 degrees C. This study developed modified YSZ with enhanced high-temperature thermal properties owing to the addition of various rareearth doping elements. Among the various rare earth-doped compositions, all the thermal properties were significantly improved in compositions containing scandium, gadolinium, and dysprosium. Furthermore, in the selected compositions, the high-temperature thermal properties were analysed under heat treatment conditions of 1300 degrees C, with a target turbine inlet temperature (TIT) of 1500 degrees C. The high-temperature phase stability of the tetragonal phase was significantly improved in the newly developed compositions, and they exhibited glass-like low thermal conductivity (similar to 0.984 W/mK) due to the influence of lattice distortion caused by the differences in the substituent-ion mass and size, and the oxygen vacancies. Moreover, there was notable improvement in the thermal expansion coefficient (similar to 11 x 10(-6)/K) and resistance to high-temperature densification.