MICROSTRUCTURAL STUDY OF THE INTERFACE REACTION BETWEEN TITANIA WHISKERS AND ALUMINUM

Titania (TiO2) whiskers have been used to react with aluminum to fabri cate composite materials. By reaction squeeze-casting, aluminum compos ites reinforced with the hard phases alpha Al2O3 and TiAl3 can be fabr icated. A characteristic of this process is that the reaction is too d rastic to control. Owing to the volume shrinkage during the reaction, the metallographical structure of the composite so prepared is heterog eneous. By squeeze casting at a lower temperature, however, a macrosco pically non-reacted TiO2/Al composite can be fabricated. At the interf ace there is only a continuous TiO layer with a thickness of similar t o 10-20 nm. After heat-treatment of the TiO2/Al composite at 800 degre es C, a new Al2O3/TiAl3 composite is prepared by the reaction: 3TiO(2) + 2Al-->3TiO + gamma Al2O3, 3TiO + 2Al-->3Ti + alpha Al2O3, Ti + 3Al- ->TiAl3,. The Vickers hardness increases with heating time, as does th e quantity of matrix defects caused by the volume shrinkage accompanyi ng the reaction, and hence the flexural strength degrades with heating time. (C) 1997 Elsevier Science Limited.