Synthesis of Al{sub 2}O{sub 3}-Al composites by reactive metal penetration
- Sandia National Labs., Albuquerque, NM (United States). Advanced Materials Lab.
- Pask Research and Engineering, Berkeley, CA (United States)
Ceramic-metal composites have been made to near net-shape by reactive penetration of dense ceramic preforms by molten Al. Ceramic-metal composite formation by reactive metal penetration is driven by a strongly negative Gibbs energy for reaction. For Al, the general form of the reaction is (x + 2)Al + (3/y)MO{sub y} {yields} Al{sub 2}O{sub 3} + M{sub 3/y}Al{sub x}, where MO{sub y} is an oxide that is wet by molten Al. In low P{sub O{sub 2}} atmospheres and at temperatures above about 900 C, molten Al reduces mullite to produce Al{sub 2}O{sub 3} and silicon. The Al/mullite reaction has a {Delta}G{degree}{sub r} (1,200 K) of {minus}1,014 kJ/mol and, if the mullite is fully dense, the theoretical volume change on reaction is less than 1%. Experiments with commercial mullite containing a silicate grain boundary phase average less than 2% volume change on reaction. In the Al/mullite system, reactive metal penetration produces a fine-grained alumina skeleton with an interspersed metal phase. With enough excess aluminum, mutually interpenetrating ceramic-metal composites are produced. Properties measurements show that ceramic-metal composites produced by reactive metal penetration of mullite by Al have a Young`s modulus and hardness similar to that of Al{sub 2}O{sub 3}, with improved fracture toughness ranging from5 to 9 MPa {center_dot} m{sup 1/2}. For penetration times less than 1 h, reaction layer thickness varies as the square root of time, which allows ceramic-metal composite coatings to be fabricated by controlling the penetration time.
- Research Organization:
- Sandia National Laboratory
- DOE Contract Number:
- AC04-76DP00789; AC04-94AL85000
- OSTI ID:
- 203536
- Journal Information:
- Journal of the American Ceramic Society, Journal Name: Journal of the American Ceramic Society Journal Issue: 1 Vol. 79; ISSN 0002-7820; ISSN JACTAW
- Country of Publication:
- United States
- Language:
- English
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