To solve the key problems faced by abradable seal coatings for SiCf/SiC ceramic matrix composites under the demand of high thrust-to-weight ratio of future aero-engines, such as high-temperature oxidation resistance, thermal expansion matching and abradability, the work aims to develop a new type of abradable environmental barrier coating system and systematically evaluate its high-speed friction and wear behavior and high-temperature gas corrosion behavior. A three-layer coating of Si/Yb2Si2O7(dense)/Yb2Si2O7 (porous) was prepared on 9 SiCf/SiC outer ring test pieces by ultra-low pressure plasma spraying combined with high-energy plasma spraying. Six pieces were subjected to high-temperature and high-speed abradable tests at 1 100 ℃, with a blade tip linear velocity of 500 m/s, and radial feed rates of 3-5 μm/s and 200-300 μm/s. Three pieces were subjected to high-temperature gas corrosion test (cumulative 500 h) at 1 350 ℃ in an atmosphere containing calcium- magnesium-aluminum-silicon sediments(CMAS) and water vapor. The properties were characterized by mass wear ratio, height wear ratio (IDR), morphology and energy spectrum analysis. When the radial feed rate was 3-5 μm/s, the coating mass wear ratio was 1.162%-3.377%, the blade mass wear ratio was ≤0.081%, the effective IDR was 21.58%-24.39%, and the scraped surface was flat without spalling. When the feed rate was 200-250 μm/s, the IDR was 16.42%-20.07%, and the coating remained in good condition, but the coating and the substrate were completely damaged at 300 μm/s. After gas corrosion, the overall weight loss of the coating was only 0.012-0.026 g, and erosion pits and microcracks appeared on the surface, but no large-area spalling occurred. CMAS exhibited soft erosion, and reacted with ytterbium silicate to form bulge-like products with pores. The cross-section of the coating was complete with good bonding. The coating exhibits excellent abradability when the radial feed rate is ≤250 μm/s, and can effectively protect the blade. After corrosion by 1 350 ℃ high-temperature gas and CMAS, the coating maintains structural integrity with only local coupled damage, which significantly improves the erosion resistance and corrosion resistance of SiCf/SiC composites.
In this work, high-quality nanostructured rare-earth silicate agglomerated powder feedstock is successfully prepared through process control. The powder feedstock exhibits excellent thermophysical properties, which are conducive to enhancing the CMAS corrosion resistance and thermal shock resistance of environmental barrier coatings (EBCs), thereby providing a solid material foundation for the fabrication of ultra-high-temperature nanostructured environmental barrier coatings. The corrosion behavior under a coupled 1 800 ℃ water vapor-oxygen-CMAS corrosive environment is simulated with an integrated combustion-environment coating testing platform. Meanwhile, by coupling with leading domestic high-temperature and high-speed abradability testing facilities, the corrosion resistance and abradability of coated typical components of high- pressure turbine outer ring blocks are evaluated. The coatings demonstrate outstanding abradability and corrosion resistance. Furthermore, an equivalent evaluation methodology for environmental barrier coatings under simulated service environments is successfully established, providing strong support for more accurate assessment of long-term service reliability of the coatings. This work will offer effective protection for ceramic matrix composite hot-section components in future advanced aerospace engines, promote the practical application of ceramic matrix composites and environmental barrier coatings in advanced engine models, and hold significant implications for the development of national defense and military capabilities in China.
Key words
abradable seal coating /
environmental barrier coating /
SiCf/SiC composite /
high-speed friction and wear /
high-temperature gas corrosion /
CMAS
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