Influence of BN microstructure on oxidation of SiC/BN/SiC composites
File(s)
Author(s)
Type
Journal Article
Abstract
This study investigates the effects of boron nitride (BN) coating characteristics on the subsurface oxidation behavior of SiC/SiC composites in high-temperature, water-rich environments. Three types of coatings were examined: a crystalline stoichiometric BN, an amorphous BN, and a Si-doped amorphous BN, the latter two containing 5–10 at% of oxygen and carbon. High-resolution imaging and chemical analysis techniques were used to probe microstructural changes after oxidation at 1000°C for 1 or 12 h in flowing 20 vol% H2O, focusing on effects of coating thickness. Complementary chemical thermodynamic calculations and models for reaction- and transport-controlled recession were used to interpret the experimental findings. Crystalline BN coatings produce open recession channels without forming borosilicate glass, a consequence of carbothermal reduction arising from C/CO produced through concomitant SiC oxidation. The combination of active oxidation and the relatively thick coatings in this system (ca. 1 µm) leads to a recession rate controlled by the intrinsic BN volatilization rate rather than the rate of gas transport. In contrast, amorphous coatings, both undoped and Si-doped, readily oxidize to form borosilicate glasses that replace the BN. Broadly, the recession lengths increase with coating thickness. In the early stages, while the glass is boria-rich and thus permeable to environmental oxidants, recession is controlled by the BN oxidation rate. As boria volatilizes, the silica concentration in the glass increases, eventually reaching the saturation limit and precipitating solid silica on the internal surfaces, essentially arresting further recession.
Date Issued
2025-03-01
Date Acceptance
2024-10-07
Citation
Journal of The American Ceramic Society, 2025, 108 (3)
ISSN
0002-7820
Publisher
Wiley
Journal / Book Title
Journal of The American Ceramic Society
Volume
108
Issue
3
Copyright Statement
Copyright © 2024 The American Ceramic Society. This is the author’s accepted manuscript made available under a CC-BY licence in accordance with Imperial’s Research Publications Open Access policy (www.imperial.ac.uk/oa-policy)
License URL
Subjects
BN
BORON-NITRIDE COATINGS
CHEMICAL-VAPOR INFILTRATION
DEPOSITION
HIGH-TEMPERATURE OXIDATION
INTERMEDIATE-TEMPERATURE
INTERPHASE
Materials Science
Materials Science, Ceramics
MATRIX COMPOSITE
oxidation
Science & Technology
SiC/SiC composite
Technology
TEM
TENSILE-STRESS RUPTURE
volatilization
water vapor
Publication Status
Published
Article Number
e20230
Date Publish Online
2024-10-23