Effect of Flash Sintering on the Structure and Durability of YSZ Thermal Barrier Coatings

Thermal barrier coatings (TBCs) based on yttria-stabilized zirconia (YSZ) are essential for the protection of nickel-based alloy blades, predominantly fabricated via air plasma spraying (APS). However, due to the inherent limitations of APS, the actual service life of YSZ TBCs does not meet practical requirements. Consequently, enhancing the service life of YSZ TBCs is crucial for practical application. The work aims to use flash sintering (FS) as an innovative post-treatment method for YSZ TBCs prepared by APS to significantly improve the durability. A systematic analysis was performed on the porosity, mechanical properties (including hardness, fracture toughness, and brittleness index), and phase composition of the coatings before and after flash sintering treatment with a Scanning Electron Microscope (SEM), X-ray Diffraction Spectrometer (XRD), and Vickers hardness tester. Additionally, the thermal cycling and high-temperature oxidation trials, facilitated by a combustion chamber experimental setup and a high-temperature furnace, were employed to thoroughly assess the enhanced durability of the coatings after FS treatment. The results revealed that the YSZ TBCs both exhibited tetragonal zirconia (t'-ZrO2) before and after flash sintering treatment. The porosity and microcracks on the coating surface were effectively alleviated, resulting in a lamellar microstructure with an 83.68% reduction in porosity and a 31.60% decrease in brittleness index, thereby significantly enhancing the mechanical properties. After flash sintering treatment, the porosity, fracture toughness, and brittleness index of the YSZ thermal barrier coatings reached 3.47%, 2.44 MPa·m1/2, and 3.94 µm−1/2, respectively. Pearson linear correlation fitting revealed a good fit between multiple parameters (e.g., porosity, hardness, fracture toughness, and brittleness index) of the coatings after flash sintering treatment and current density, with adjusted R2 values exceeding 0.91 for all. The actual performance of the YSZ thermal barrier coatings was effectively regulated based on current density. Repeated validation under the same process parameters showed that the coefficients of variation for porosity, fracture toughness, and brittleness index were 0.273, 0.077, and 0.062, respectively, demonstrating the good stability of flash sintering technology for the secondary treatment of YSZ TBCs. After 100 thermal cycles, the spallation area ratio of the APS-TBC was approximately 40%, displaying irregular spallation edges and extensive spallation regions, whereas the maximum spallation ratio of the FS-TBC was nearly 10%. During high-temperature oxidation, the growth rate of the thermally grown oxide (TGO) layer significantly accelerated when the oxidation temperature exceeded 1 100 ℃, with temperature exerting a more substantial effect than oxidation time. TGO growth predominantly occurred in the early stages of oxidation. Following 500 hours of oxidation at 1 200 ℃, the TGO layer thickness of the FS-TBC was reduced by 30.00% compared to the APS-TBC, with the TGO thickness of the FS-TBC after 500 hours equivalent to that of the APS-TBC after 100 hours. The TGO growth rates for APS-TBC and FS-TBC within the first 50 hours were 0.092 µm/h and 0.050 µm/h at 1 200 ℃, respectively. During the period of 50 to 500 hours, the TGO growth rates for APS-TBC and FS-TBC were 0.008 µm/h and 0.007 µm/h at 1 200 ℃, respectively. Overall, flash sintering treatment significantly promotes the densification of YSZ TBCs and engenders pronounced improvements in mechanical properties, damage tolerance, and overall durability under both thermal cycling and high-temperature oxidizing conditions, evidencing FS's potential as an effective secondary treatment for enhancing the performance of APS-prepared YSZ TBCs. © 2025 Chongqing Wujiu Periodicals Press. All rights reserved.