Thermo-physical properties, morphology and thermal shock behavior of EB-PVD thermal barrier coating with DLC YbGdZrO/YSZ system

Abstract

(Yb0.1Gd0.9)2Zr2O7 (YbGdZrO) rare earth modified zirconate ceramics is one of the novel thermal barrier coatings (TBCs) materials which has attracted much attention in recent years and is suitable for higher temperature applications. YbGdZrO ceramic powders gained from solid-phase synthesis show a single defect fluorite structure. After calcined at 1723 K upon 400 h, whose powder does not form any new phases and exhibit outstanding thermal durability. The thermal expansion coefficient of YbGdZrO ceramics with the elevated temperature to 1573 K is attained to 10.76 × 10−6 K−1, which is slightly smaller than that of Gd2Zr2O7 (GZO) material (10.98 ×10−6 K−1) at the same temperature. The arithmetic mean of coefficient of thermal diffusion of YbGdZrO bulks measured at 1273 K is 0.385 mm2/s, that seems to be equivalent to that of GZO ceramics (0.388 mm2/s, 1273 K). The X-ray diffraction feature peaks of electron beam physical vapor deposition (EB-PVD) YbGdZrO ceramic coatings almost resemble to its ingot, except that the crystal face indices of their two strongest peaks are different. The pyramid-like shape can be scrutinized on top tip of columnar grain of the as-deposited YbGdZrO ceramic layer, which is associated to the cubic lattice in the fluorite structure. After 3000 cycles of flame thermal shock, the upper half of the coated sample surface occurs light green. While the closer is the position to edge of the specimen, the more obvious is the color. In addition, many small black spots with disorderly distribution are observed on the coating surface. A large number of irregularly distributed and cross-linked micro-cracks are displayed on the surface of YbGdZrO ceramic top layer as well as the averaged width of these micro-cracks is determined to be ∼8.523 µm. Although the ceramic coating appears to have a small number of layered exfoliation, the chemical composition of the exposed region still contains only elements of Yb, Gd, Zr and O. It does not stretch to either interface of double-ceramic-layer (DCL) YbGdZrO/YSZ or interior of YSZ ceramic coating.