Phase transformations in multilayered CVD mullite coatings
- Boston Univ., MA (United States). Dept. of Manufacturing Engineering
Mullite (3Al{sub 2}O{sub 3} {center_dot} 2SiO{sub 2}) is an ideal candidate for coatings on SiC due to its toughness, corrosion resistance and coefficient of thermal expansion (CTE) match. The authors have deposited alternating layers of Al{sub 2}O{sub 3} and SiO{sub 2} followed by post deposition heat treatment to induce mullite formation at the interface. The authors found that the devitrification of silica to crystobalite led to spallation of the multilayered coatings due to the fracture within the crystalline silica layers. To understand this transformation better, the authors studied the effect of pressure and temperature on devitrification of silica in both bulk and in coating form. The authors have demonstrated that the difference in specific volumes of the two phases plays a key role in the vitreous to crystalline transformation in silica.
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 82555
- Report Number(s):
- CONF-941144--; ISBN 1-55899-264-2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ALUMINIUM CHLORIDES
ALUMINIUM OXIDES
CHEMICAL REACTION KINETICS
CHEMICAL VAPOR DEPOSITION
CRACKS
CRISTOBALITE
CRYSTAL-PHASE TRANSFORMATIONS
HEAT TREATMENTS
MULLITE
RESIDUAL STRESSES
SCANNING ELECTRON MICROSCOPY
SILANES
SILICON OXIDES
TRANSMISSION ELECTRON MICROSCOPY
X-RAY DIFFRACTION