Exceptional hot corrosion resistance behavior and mechanism of double layered Zr6Ta2O17/YSZ thermal barrier coatings exposed to Na2SO4-V2O5 salt

Abstract

Single-ceramic-layered YSZ thermal barrier coatings (TBCs) and double- ceramic-layered Zr₆Ta₂O₁₇/YSZ TBCs were deposited using atmospheric plasma spray (APS). Hot corrosion tests were conducted by exposing the coatings to 50 wt% Na₂SO₄-50 wt% V₂O₅ molten salt at temperatures of 800 ℃, 900 ℃ and 1000 ℃ for durations of 8 h, 24 h and 48 h respectively. The hot corrosion behavior and mechanism of the coatings were discussed. All corroded YSZ coatings exhibited severe edge cracking, peeling, and surface pulverization due to the significant loss of stabilizer Y₂O₃. Zr₆Ta₂O₁₇/YSZ showed superior corrosion resistance compared to traditional YSZ, which maintained intact coating structure below the medium temperature (900 ℃). This is attributed to the reaction inertness between Zr₆Ta₂O₁₇ and V₂O₅, highlighting the role of Zr₆Ta₂O₁₇ in preventing extensive surface contact between V₂O₅ and YSZ. The formation and decomposition of NaTaO₄ phase at 1000 ℃ are the main reasons for the destruction of the double-layered structure. The decomposition product Ta₂O₅ accelerated the formation of Zr₆Ta₂O₁₇/Ta₂O₅ eutectic structure; furthermore, the accumulation of Ta₂O₅ in coating defects reduced the strain tolerance. Thermodynamic calculations illustrate that (Y/La/Gd/Yb/Sm)₂O₃ has high reactivity with V₂O₅, while the reaction between Ta₂O₅ and Na₂SO₄ is thermodynamically unfavorable. The study proposes design principles for TBCs resistant to Na₂SO₄-V₂O₅ salt corrosion, emphasizing the importance of avoiding the synergistic effects of corrosion salts across all temperature ranges through multi-layer isolation.