Composite Ceramics for Thermal Barrier Coatings Produced From ZrO2 Doped with Yttrium-Subgroup Rare-Earth Metal Oxides

The use of compositionally complex ZrO2-based ceramics doped with a mixture of yttrium-subgroup rare-earth metal (REM) oxides for the deposition of thermal barrier coatings (TBCs) was studied. For research, a heavy concentrate (HC) of yttrium-subgroup REM oxides, consisting of (wt.%) 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 (including 3.2 Al2O3), and Y2O3 and M-ZrO2 powders were chosen. The targets for depositing electron-beam ceramic TBC layers-both standard and compositionally complex ones-were made of ceramic mixtures including (wt.%) M-ZrO2-7 Y2O3 and 90 M-ZrO2-10 HC. The properties of the compositionally complex and standard yttria-stabilized ZrO2-based ceramic layers in electron-beam TBCs applied in one process cycle were compared. Two-layer metal/ceramic TBCs were deposited onto model blades by directional crystallization from the ZhS-26VI alloy employing an UE-174 industrial electron-beam installation (ELTECHMACH, Vinnytsia). The ceramic M-ZrO2-7 Y2O3 topcoat was denoted as YSZ and 90 M-ZrO2-10 HC as HCSZ. The MZP-6 alloy (nickel-chromium-aluminum-yttrium) was used to form an inner heat-resistant bond coat. This resulted in rough dense glassy coatings differing by color: light-gray YSZ and dark-gray HCSZ. The coatings were 90-95 mu m thick on the blade back side and 90 mu m thick on the pressure side. Both coatings included the F-ZrO2 phase. Feather-like microstructures emerged in the coatings. The YSZ topcoat contained two types of dense structures, represented by columns and branched formations, and the HCSZ layer was of irregular microstructure with wide feather-like formations growth together. The laminar microstructure of the ceramic topcoat was due to the process features peculiar to electron-beam deposition. The YSZ topcoat had the following microhardness: 3884 MPa on the back side and 6052 MPa on the pressure side. The HCSZ topcoat had much lower microhardness: 1381 MPa on the back side and 1679 MPa on the pressure side. The compositionally complex coating withstood 161 thermal cycles and the standard coating 138 thermal cycles. Previous studies showed that ZrO2 stabilization with concentrates of yttrium-subgroup REM oxides was promising for the microstructural design of TBC ceramic topcoats.