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Phase Transformations in Multilayered CVD Mullite Coatings

Published online by Cambridge University Press:  15 February 2011

D. Doppalapudi ,
R. Muipuri ,
S. N. Basu  and
V. K. Sarin
D. Doppalapudi
Affiliation:
Department of Manufacturing Engineering, Boston University, Boston, MA 02215
R. Muipuri
Affiliation:
Department of Manufacturing Engineering, Boston University, Boston, MA 02215
S. N. Basu
Affiliation:
Department of Manufacturing Engineering, Boston University, Boston, MA 02215
V. K. Sarin
Affiliation:
Department of Manufacturing Engineering, Boston University, Boston, MA 02215
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Abstract

Mullite (3Al2O3.2SiO2) is an ideal candidate for coatings on SiC due to its toughness, corrosion resistance and coefficient of thermal expansion (CTE) match. We have deposited alternating layers of Al2O3 and SiO2 followed by post deposition heat treatment to induce mullite formation at the interface. We found that the devitrification of silica to cristobalite led to spallation of the multilayered coatings due to the fracture within the crystalline silica layers. To understand this transformation better, we studied the effect of pressure and temperature on devitrification of silica in both bulk and in coating form. We have demonstrated that the difference in specific volumes of the two phases plays a key role in the vitreous to crystalline transformation in silica.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 363 , 1994 , 95
Copyright
Copyright © Materials Research Society 1995

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