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CVD deposition of highly Al-rich mullite coatings

Published online by Cambridge University Press:  01 February 2011

Tushar Kulkarni ,
H Z Wang ,
S N Basu  and
V K Sarin
Tushar Kulkarni
Affiliation:
tushark@bu.edu, Boston University, Department of Manufacturing Engineering, 15 St. Mary's Street, Boston, MA, 02215, United States
H Z Wang
Affiliation:
hzwang2008@gmail.com, Boston University, College of Engineering, 15 St. Mary's Street, Brookline, MA, 02446, United States
S N Basu
Affiliation:
basu@bu.edu, Boston University, College of Engineering, 15 St. Mary's Street, Brookline, MA, 02446, United States
V K Sarin
Affiliation:
sarin@bu.edu, Boston University, College of Engineering, 15 St. Mary's Street, Brookline, MA, 02446, United States
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Abstract

Although chemical vapor deposited mullite (3Al2O3•2SiO2) environmental barrier coatings have shown promise in protecting Si-based substrates for gas-turbine applications, there is concern that the silica content within the mullite coating itself might be susceptible to hot-corrosion and recession during long term exposure to corrosive atmospheres. There is thus a strong motivation to substantially reduce or even virtually eliminate the silica from the surface of the mullite coatings that are in direct contact with atmospheres containing corrosive oxides and steam. Functionally graded mullite (3Al2O3•2SiO2) coatings have been grown for Si-based substrates and the composition has been tailored in these coatings, with the Al/Si ratio being stoichiometric (∼ 3) at the coating/substrate interface for coefficient of thermal expansion (CTE) match, and increasing monotonically towards the outer coating surface. These functionally graded coatings have some of the highest Al-rich mullite reported to date at the coating surface. At these extremely high Al/Si ratios, mullite structure breaks down and the formation of a nano-sized high-alumina rich phase occurs. High-resolution transmission electron microscopy has been used to characterize the structure and composition of high alumina mullite and will be discussed.

Keywords

chemical vapor deposition (CVD) (deposition)environmentally protectivetransmission electron microscopy (TEM)
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1056: Symposium HH – Nanophase and Nanocomposite Materials V , 2007 , 1056-HH09-03
Copyright
Copyright © Materials Research Society 2008

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