Microstructure and growth mechanism of Al{sub 2}O{sub 3}/Al ceramic matrix composite made by directed oxidation of Al alloys
- National Univ. of Singapore (Singapore)
Since the Lanxide process was advanced for forming of Al{sub 2}O{sub 3} ceramic composite by directed oxidation of Al alloys, much work has been done with various mechanisms being proposed. The mechanisms have claimed that only certain dopants are essential to the growth process. Nevertheless, no united consensus has yet been reached. In the present work, Al alloy containing 5% Mg was oxidized in air for 12 hours at 1,150 C with or without surface dopants of MgO or Pd. The resultant composites showed very different microstructures. Without any surface doping, the alloy did not develop any portion of composite as the initial intimate oxide film stops further oxidation. This intimate oxide film can either be broken off by mechanical means or penetrated by reaction with surface dopants, so that the composite can grow and develop. The results show that the previously reported incubation time is not only related to reaction processes but also to the initial mechanical disturbances. Doping with Pd made the composite darker in color as the grains of the alumina ceramic matrix and inclusions of Al metal are finer. This shows that Pd may make the top oxide layer less intimate, and more nucleation sites are therefore available for oxidation. A new model is presented for oxide sustained growth based on the existence of oxygen active top surface layer and the capillary flow of molten metal around ceramic phase.
- OSTI ID:
- 100550
- Report Number(s):
- CONF-941144-; ISBN 1-55899-266-9; TRN: IM9540%%21
- Resource Relation:
- Conference: Fall meeting of the Materials Research Society (MRS), Boston, MA (United States), 28 Nov - 9 Dec 1994; Other Information: PBD: 1995; Related Information: Is Part Of Ceramic matrix composites -- Advanced high-temperature structural materials; Lowden, R.A.; Ferber, M.K. [eds.] [Oak Ridge National Lab., Oak Ridge, TN (United States)]; Hellmann, J.R. [ed.] [Pennsylvania State Univ., University Park, PA (United States). Center for Advanced Materials]; Chawla, K.K. [ed.] [New Mexico Inst. of Mining and Technology, Socorro, NM (United States)]; DiPietro, S.G. [ed.] [Textron Specialty Materials, Lowell, MA (United States)]; PB: 493 p.; Materials Research Society symposium proceedings, Volume 365
- Country of Publication:
- United States
- Language:
- English
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