Phase stability, thermo-physical property and thermal cycling durability of Yb2O3 doped Gd2Zr2O7 novel thermal barrier coatings

Novel double-ceramic-layer (DCL) thermal barrier coatings (TBCs) composed of (Yb0.1Gd0.9)(2)Zr2O7 (YbGZO) top layer and YSZ bottom layer were deposited via EB-PVD technology. The phase stabilities and thermo-physical properties of the YbGZO bulk ceramics as well as the diffraction peak constituent, elemental content, microstructure and thermal exposure behavior of DCL thermal barrier coatings were evaluated. After calcination from room temperature up to 1573 K, the YbGZO ceramic powders do not form new phases and still maintain excellent thermal stability while the thermal diffusivity of YbGZO bulk reaches the minimum value of 0.207 +/- 0.004 mm(2)/s at 1273 K. Meanwhile, the thermal conductivity of YbGZO ceramics is in the range of 0.88-1.04 W/(m.K), which is correspondingly lower than that of YSZ bulk material ((1.20-1.46) W/(m.K)) due to the fact that the ceramic top layer of YbGZO has more irregular columns distribution and a larger intercolumnar gap. After spallation failure, DCL coating is mainly composed of YbGZO with fluorite phase and Y(0.08)Zr(0.92)O(1.06 )of tetragonal phase which the pyramidal morphologies on top have disappeared with an obvious densification of ceramic coatings. In comparison, the sintering behavior of YSZ coating is more serious than that of YbGZO coating. Moreover, the penetration of vertical microcracks through the whole ceramic coatings could promote the formation of oxygen diffusion channels and further accelerate the internal oxidation behavior of grain boundaries and voids within the bond coat. In addition, the irregular distribution of transverse microcracks has led to the transgranular fracture of columnar grains.