Investigation on the thermo-chemical reaction mechanism between yttria-stabilized zirconia (YSZ) and calcium--magnesium--alumino-silicate (CMAS)

Abstract

Thermal barrier coatings (TBCs) with Y₂O₃-stabilized ZrO₂ (YSZ) top coat play a very important role in advanced turbine blades by considerably increasing the engine efficiency and improving the performance of highly loaded blades. However, at high temperatures, environment factors result in the failure of TBCs. The influence of calcium--magnesium--alumino-silicate (CMAS) is one of environment factors. Although thermo-physical effect is being paid attention to, the thermo-chemical reaction becomes the hot-spot in the research area of TBCs affected by CMAS. In this paper, traditional two-layered structured TBCs were prepared by electron beam physical vapor deposition (EB-PVD) as the object of study. TBCs coated with CMAS were heated at 1240°C for 3 h. Additionally, 15 wt.% simulated molten CMAS powder and YSZ powder were mixed and heated at 1240°C or 1350°C for 48 h. SEM and EDS were adopted to detect morphology and elements distribution. According to XRD and TEM results, it was revealed that CMAS react with YSZ at high temperature and form ZrSiO₄, Ca_0.2Zr_0.8O_1.8 and Ca_0.15Zr_0.85O_1.85 after reaction, as a result, leading to the failure of TBCs and decreasing the TBC lifetime.

Keywords

thermal barrier coating (TBC) / yttria-stabilized zirconia (YSZ) / calcium--magnesium--alumino-silicate (CMAS) / thermo-chemical reaction / high temperature

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