Hot corrosion behavior of La₂Ce₂O₇ thermal barrier coatings under high-temperature molten salt environments

Abstract

In this study, La₂Ce₂O₇ (LC) powders synthesized via a molten-salt process were deposited as a thermal barrier coating on Hastelloy-X substrates by atmospheric plasma spraying (APS), with a NiCrAlY bond coat as an interlayer. The APS-deposited LC coating exhibited phase stability up to 1600 °C for 100 h while retaining its fluorite structure. The thermal conductivity of the coating remained low, ranging from 0.64 to 0.82 W·m⁻¹ ·K⁻¹ over the temperature range of 30–1000 °C. The coating was further subjected to thermal cycling tests to evaluate its thermal cycling lifetime and failure behavior, during which chipping-type spallation developed within the ceramic topcoat near the bond-coat interface due to thermally induced stresses. Hot-corrosion tests were performed in Na₂SO₄, V₂O₅, and a eutectic mixture consisting of 32 wt% Na₂SO₄–68 wt% V₂O₅ at 900 °C for 30 h. The coating exhibits high stability in pure Na₂SO₄ and moderate degradation in V₂O₅. In contrast, severe degradation is observed in the Na₂SO₄–V₂O₅ eutectic mixture, where LaVO₄ forms as the dominant corrosion product, accompanied by CeVO₄, LaCeVO₄, and CeO₂. This study presents a coating-level evaluation of the high-temperature phase stability of APS-deposited La₂Ce₂O₇ coatings, together with a systematic assessment of their hot-corrosion behavior in sulfate- and vanadate-containing service environments.