Composite Ceramics for Thermal-Barrier Coatings Produced from Zirconia Doped with Rare Earth Oxides

The thermal fatigue life of zirconia-based complex composite ceramics doped with a mixture of rare earth oxides was studied. Two concentrates of rare earth oxides were chosen (wt.%): 1) cerium- subgroup concentrate of composition 62.4 CeO2, 13.5 La2O3, 10.9 Nd2O3, 3.9 Pr6O11, 0.92 Sm2O3, 1.2 Gd2O3, 0.24 Eu2O3, 2.66 ZrO2, 1.2 Al2O3, 1.7 SiO2, and 1.38 other oxides (light concentrate (LC)) and 2) yttrium-subgroup concentrate of composition 13.3 Y2O3, 1.22 Tb4O7, 33.2 Dy2O3, 8.9 Ho2O3, 21.8 Er2O3, 1.86 Tm2O3, 12.5 Yb2O3, 0.57 Lu2O3, and 6.65 other oxides (heavy concentrate (HC)). Two-layer metal/ceramic thermal-barrier coatings (TBCs) were deposited on gas turbine engine blades by electron-beam physical vapor deposition (EB-PVD) in one process cycle. The properties of ZrO2–LC and ZrO2–HC TBC ceramic top coats were compared to those of a standard yttria-stabilized zirconia layer (ZrO2–Y2O3). The thermal fatigue experiment was performed by heating the samples to 1100°C in a muffle furnace for 5 min, holding them at this temperature for 50 min, and cooling in water for 5 min. The standard ZrO2–Y2O3 layer withstood 138 thermal cycles, while the ZrO2–LC and ZrO2–HC layers withstood 161 thermal cycles. The porous microstructure of the ceramic layers developed during thermal cycling was found to depend on laminar microstructures acquired by the layers in the EB-PVD process. The number of spherical pores in the ZrO2–LC and ZrO2–HC layers was much higher than in the ZrO2–Y2O3 layer. This increased their thermal fatigue life by 16% compared to the standard coating. An integrated approach to the choice of the ceramic top coat composition based on ZrO2 solid solutions doped with natural rare earth oxide concentrates and of the technique for their deposition, as well as improvement in the coating architecture, will promote cost-effective TBCs with the properties required.