Current Status Of Environmental Barrier Coatings For Si Based Ceramics

A silicon bond coat an intermediate mullite 3al 2 o 3 sio2 or mullite sas 1 x.

Current status of environmental barrier coatings for si based ceramics.

In the late 1980s and early 1990s a wide range of refractory oxide materials were tested as coatings on si based ceramics to provide protection from hot corrosion. Advanced environmental barrier coatings ebcs are being developed for next generation gas turbine engines to protect engine hot section sic based lightweight components in the harsh operating combustion environments and extend component lifetimes. Mi mullite cas bsas si b 100 µm std sic sic mullite cas bsas a 100 µm figure 1. Lee surface and coatings technology current status of environmental barrier coatings for si based ceramics 133 134 1 7 2000.

Currently plasma sprayed external environmental barrier coatings ebcs are the most promising approach. The current work considers a multi layered barium strontium. The earlier ebcs consist of a mullite bond layer and an yttrium stabilized zirconia ysz top coating. In the past few decades ebc s have been used as a protective layer for si based non oxide ceramics substrate that inhibits the corrosion in the presence of water vapor and molten salt.

A novel high entropy material yb 0 2 y 0 2 lu 0 2 sc 0 2 gd 0 2 2 si 2 o 7 5re 0 2 2 si 2 o 7 was prepared by the sol gel method and investigated as a promising environmental barrier coating ebc for sic based composites the results of x ray diffraction and transmission electron microscopy indicated that rare earth elements were distributed homogeneously in the single monoclinic phase. The goal was to fabricate an yb 2 si 2 o 7 coating layer with high oxidation resistance at high temperatures and a thermal expansion coefficient similar. Cross section of mullite cas bsas coated sic sic after 200h at 1225oc with 1h cycles in 90 h2o balance o2. Carbon fiber reinforced silicon carbide composites c sic are promising materials for high temperature light weight structural components.

In this study yb 2 si 2 o 7 was selected as an environmental barrier coating ebc with improved high temperature chemical stability to combat the disadvantages of si based non oxide ceramics. To understand the failure mechanism or to predict the spallation life of environmental barrier coatings ebc on fiber reinforced ceramic matrix composites the fracture strength of ebc and the process of the crack growth in ebc layers need to be experimentally determined under standard or simulated engine operating conditions. Current ebc systems use multiple layers each serving unique requirements. However a protective coating and environmental barrier coating ebc are necessary to prevent the oxidation of the carbon and the reaction of the formed silica scale with water vapor.