Peter Pontiller and M. Willert-Porada High Temperature Behavior of Si3N4 and Yb2SiO5 Coated Carbon Fibers for Silicon-Nitride CMC Advanced Engineering Materials 16
Two different coatings are compared: reactive CVD-derived Si3N4 coatings to investigate C-fiber-matrix reactions and Yb-silicate coatings to reveal potential reactions with the Yb-silicate additive serving as sintering aid for Si3N4. A new ceramic phase – an Yb-carbido-nitiridosilicate, Yb2Si4CN6–is found as product of carbothermal reduction of the Yb-silicate. The carbothermal reduction occurs also with other RE-silicates, RE = Yb, Er, Y, Gd, and Sm while SiC is found as reaction product on carbon fibers coated with Si3N4. The role of Yb2Si4CN6 as reinforcement for Si3N4-CMC is discussed based on bond strength comparison of carbides (SiC), nitride silicates (SiAlON), and nitrides (Si3N4).
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