COMPOSITE CERAMICS FOR THERMAL-BARRIER COATINGS PRODUCED FROM ZrO₂ COMPLEXLY DOPED WITH OXIDES OF RARE EARTH ELEMENTS 

Abstract

The thermal fatigue life of zirconia-based complex composite ceramics complexly doped with a mixture of REE oxides was studied. Two concentrates of REE oxides were chosen (wt.%): (1) concentrate of the cerium subgroup 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 in total (light concentrate (LC)) and (2) concentrate of the yttrium subgroup 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 in total (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 layers were compared to those of a standard yttria-stabilized zirconia layer (ZrO₂–Y₂O₃). The thermal fatigue life experiment was performed by heating the samples to 1100 °С 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 formed during thermal cycling was found to depend on the 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 increases their thermal fatigue life by 16% compared to the standard coating. An integrated approach to the choice of the ceramic layer composition based on ZrO₂ solid solutions complexly doped with oxide concentrates of rare earth elements of natural origin and the technique for their deposition and improvement in the coating architecture will promote cost-effective TBCs with the properties required.