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High Temperature Behavior of Si 3 N 4 and Yb 2 SiO 5 Coated Carbon Fibers for Silicon‐Nitride CMC
Author(s) -
Pontiller Peter,
WillertPorada M.
Publication year - 2014
Publication title -
advanced engineering materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.938
H-Index - 114
eISSN - 1527-2648
pISSN - 1438-1656
DOI - 10.1002/adem.201300443
Subject(s) - materials science , carbothermic reaction , sintering , ceramic , ceramic matrix composite , fiber , silicon , coating , carbon fibers , oxide , silicon nitride , composite material , silicate , chemical engineering , metallurgy , composite number , carbide , engineering
For oxide‐free ceramic matrix composites (CMC), with Si 3 N 4 matrix and carbon fiber reinforcement, for extreme high temperature applications, protective coatings of the C‐fibers are investigated. Two different coatings are compared: reactive CVD‐derived pure Si 3 N 4 coatings to investigate C‐fiber‐matrix reactions and powder based Yb‐silicate coatings to reveal potential reactions with the Yb‐silicate additive serving as sintering aid for Si 3 N 4 . The reactivity toward carbon in nitrogen atmosphere is studied in the temperature interval from 20 °C up to 1700 °C. A new ceramic phase – an Yb‐carbido‐nitiridosilicate , Yb 2 Si 4 CN 6 –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 pure Si 3 N 4 . The oxidation resistance of the coated fibers in air was investigated in the temperature interval up to 1000 °C, and the apparent activation energy of oxidation was analyzed based on DTA‐EGA results. The oxidation kinetic reveals a significant increase of onset point of oxidation temperature by up to 150 K for Si 3 N 4 coated short carbon fibers obtained from the reactive CVD coating process. Such fibers have a high application potential for carbon‐fiber reinforced Si 3 N 4 ‐CMC. The role of Yb 2 Si 4 CN 6 as reinforcement for Si 3 N 4 ‐CMC is discussed based on bond strength comparison of carbides (SiC), nitride silicates (SiAlON), and nitrides (Si 3 N 4 ).