Composition optimization, high-temperature stability, and thermal cycling performance of Sc-doped Gd₂Zr₂O₇ thermal barrier coatings: Theoretical and experimental studies

Sc was doped into Gd₂Zr₂O₇ for expanding the potential for thermal barrier coating (TBC) applications. The solid solution mechanism of Sc in the Gd₂Zr₂O₇ lattice, and the mechanical and thermophysical properties of the doped Gd₂Zr₂O₇ were systematically studied by the first-principles method, based on which the Sc doping content was optimized. Additionally, Sc-doped Gd₂Zr₂O₇ TBCs with the optimized composition were prepared by air plasma spraying using YSZ as a bottom ceramic coating (Gd-Sc/YSZ TBCs), and their sintering behavior and thermal cycling performance were examined. Results revealed that at low Sc doping levels, Sc has a large tendency to occupy the lattice interstitial sites, and when the doping content is above 11.11 at%, Sc substituting for Gd in the lattice becomes dominant. Among the doped Gd₂Zr₂O₇, the composition with 16.67 at% Sc content has the lowest Pugh’s indicator (G/B) and the highest Poisson ratio (σ) indicative of the highest toughness, and the decreasing trends of Debye temperature and thermal conductivity slow down at this composition. By considering the mechanical and thermophysical properties comprehensively, the Sc doping content was optimized to be 16.67 at%. The fabricated Gd-Sc coatings remain phase and structural stability after sintering at 1400 ℃ for 100 h. Gd-Sc/YSZ TBCs exhibit excellent thermal shock resistance, which is related to the good thermal match between Gd-Sc and YSZ coatings, and the buffering effect of the YSZ coating during thermal cycling. These results revealed that Sc-doped Gd₂Zr₂O₇ has a high potential for TBC applications, especially for the composition with 16.67 at% Sc content.