Transmission electron microscopy observations on phase transformations during aluminium/mullite composites formation by gas pressure infiltration
- Silesian University of Technology, Institute of Engineering Materials and Biomaterials, Konarskiego 18A, 44-100 Gliwice (Poland)
- Silesian Centre for Education and Interdisciplinary Research, 75 Pułku Piechoty 1A, 41-500 Chorzów (Poland)
The porous ceramic preforms were manufactured using the powder metallurgy technique. First, the start-up material (halloysite with the addition of carbon fibres as the pore-forming agent) was slowly heated to 800 °C and then sintered at 1300 °C. Degradation of the carbon fibres enabled the open canals to form. At the end of the sintering process, the porous ceramic material consisting mainly of two phases (mullite and cristobalite) was formed, without any residual carbon content. During infiltration, the liquid metal filled the empty spaces (pores) effectively and formed the three-dimensional network of metal in the ceramic. The cristobalite was almost entirely decomposed. In the areas of its previous occurrence, there are new pores, only in the ceramic grains. The mullite, which was formed from halloysite during annealing, crystallized in the Pbam orthorhombic space group, with the (3Al{sub 2}O{sub 3}·2SiO{sub 2}) stoichiometric composition. The mullite structure does not change during the infiltration. The composite components are tightly connected. A transition zone between the ceramics and the metal, having the thickness of about 200 nm, was formed. The nanocrystalline zone, identified as γ-Al{sub 2}O{sub 3}, was formed by diffusing the product of the cristobalite decomposition into the aluminium alloy matrix. There is an additional, new phase, identified as (Mg,Si)Al{sub 2}O{sub 4} in the outer parts of the transition zone. - Highlights: • Phase changes after the infiltration of aluminium into porous mullite preforms were observed by TEM. • TEM observations confirm that during infiltration cristobalite was decomposed and the structure of mullite did not change. • Between the ceramic and the metal, a transition zone comprising a layer of γ-Al{sub 2}O{sub 3} and (Mg,Si)Al{sub 2}O{sub 4} was formed.
- OSTI ID:
- 22587124
- Journal Information:
- Materials Characterization, Vol. 114; Other Information: Copyright (c) 2016 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 1044-5803
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
77 NANOSCIENCE AND NANOTECHNOLOGY
ALUMINIUM
ALUMINIUM ALLOYS
ALUMINIUM OXIDES
CARBON
CARBON FIBERS
CERAMICS
CRISTOBALITE
LIQUID METALS
MULLITE
NANOSTRUCTURES
ORTHORHOMBIC LATTICES
PHASE TRANSFORMATIONS
POROUS MATERIALS
POWDER METALLURGY
SINTERING
TRANSMISSION ELECTRON MICROSCOPY
X-RAY DIFFRACTION