Hot corrosion and mechanical properties of nanostructured Al₂O₃/CSZ composite TBCs

Abstract

The purpose of this research is to improve the quality and efficiency of yttria-stabilised zirconia (YSZ) thermal barrier coating (TBC) through replacing CSZ. Three types of top coats including conventional YSZ, CSZ and nanostructured Al₂O₃/CSZ composite were applied, by thermal spray technique, on IN738LC base metal and the results were compared to one another. In the present investigation, hot corrosion behaviours of the coatings were tested in a furnace containing a mixed environment of Na₂SO₄ and V₂O₅ salts at 1050°C. Nanoindentation tests were used to evaluate mechanical properties of the coatings. The experimental results confirmed that nanostructured Al₂O₃/CSZ composite coating had much hot corrosion resistance than those of conventional TBCs. The transformation of tetragonal zirconia to monoclinic ZrO₂ and formation of YVO₄ and CeVO₄ crystals as hot corrosion products led to the degradation of the mentioned TBCs. Microstructural analysis indicated that the penetration of molten salt was much less in the nanostructured Al₂O₃/CSZ composite coating where the infiltration of both oxygen and aggressive molten salt was reduced. Mechanical results showed that the superior mechanical properties of nanostructured Al₂O₃/CSZ composite coating may be attributed to its structural stability.

Keywords:

• YSZ
• CSZ
• nanostructured Al₂O₃/CSZ
• hot corrosion
• nanoindentation: mechanical properties