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D.Z. Wang School of Materials Science and Engineering, Harbin Institute of Technology, P.O. Box 433, Harbin, 150001, People’s Republic of China (Received 1 December 1999; accepted 19 June 2000)
A fully dense in situ Al3Ti–Al2O3 intermetallic matrix composite containing about 30 vol% Al2O3 particles was prepared by combining squeeze casting with combustion synthesis using the chemical reaction between TiO2 and Al. The microstructure of the in situ composite was examined using x-ray diffraction, scanning electron microscopy, and transmission electron microscopy techniques. Compressive behavior of the composite was investigated in the temperature range of 25–600 °C and compared with that of the as-cast Al3Ti alloy. The in situ formed spherical ␣–Al2O3 particles with a size of 0.2–1 m were uniformly distributed in the Al3Ti matrix. The grain size of the Al3Ti matrix containing a small amount of Al2Ti precipitate was 2–10 m. The compressive strength of the in situ composite was about 6–9 times that of the as-cast monolithic Al3Ti alloy and could be maintained at temperatures up to 600 °C. This was mainly attributed to the fine grain size of Al3Ti matrix and the rule of mixture strengthening of Al2O3 particles. The existence of Al2Ti phase and high dislocation density in the matrix also contributed positively to the composite strength.
I. INTRODUCTION
Much attention has been paid to the development and application of metal-matrix composites and intermetallic matrix composites.1 Traditionally, they have been produced by such processing techniques as powder metallurgy, 2 rapid solidification, 3 and diverse casting techniques (e.g., squeeze casting).1 In all these techniques, the reinforcing phase (Al2O3 particulate for instance) is first mixed with the matrix materials. The scale of the reinforcing phase is consequently constrained by the starting powder size, which is typically of the order of a few microns to a few tens of microns and rarely below 1 m.1 In the last ten years, new in situ processing technologies for fabricating metal and ceramic composites have emerged. In situ techniques use chemical reactions for the formation of the reinforcement. These technologies include self-propagating high-temperature synthesis (SHS), direct metal oxidation method (DIMOX™), exothermic dispersion (XD™), mechanical alloying,4–9 and reactive infiltration10–13 or reaction powder metallurgy.14,15 Because of the fineness and thermodynamic stability of the reinforcing phase, it is expected that in situ composites should offer excellent dispersion of J. Mater. Res., Vol. 15, No. 9, Sep 2000
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fine reinforcing particles and nascent interface, resulting in better mechanical properties and high-temperature performance. Another advantage of in situ techniques is their capability for processing materials or composites that could be difficult to obtain by other conventional methods, such as Al–Ti-based composites.11,16 Al3Ti has a lower density and better oxidation resistance than othe
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