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Titania (TiO2) whiskers have been used to react with aluminum to fabricate composite materials. By reaction squeeze-casting, aluminum composites reinforced with the hard phases α Al2O3 and TiAl3 can be fabricated. A characteristic of this process is that the reaction is too drastic to control. Owing to the volume shrinkage during the reaction, the metallographical structure of the composite so prepared is heterogeneous. By squeeze casting at a lower temperature, however, a macroscopically non-reacted TiO 2 Al composite can be fabricated. At the interface there is only a continuous TiO layer with a thickness of ~10–20 nm. After heat-treatment of the TiO 2 Al composite at 800 °C, a new Al 2 O 3 TiAl 3 composite is prepared by the reaction: 3TiO2 + 2Al→3TiO + γAl2O3, 3TiO + 2Al→3Ti+αAl2O3, Ti+3Al→TiAl3. The Vickers hardness increases with heating time, as does the quantity of matrix defects caused by the volume shrinkage accompanying the reaction, and hence the flexural strength degrades with heating time. |
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