Synthesis and Secondary Processing of High-Strength Aluminum Matrix Composites by Reactive Sintering

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Aluminum matrix composites reinforced with ceramic particulates (Al_2O_3, TiB_2 or TiC) were synthesized via reactive sintering of Al-B-TiO_2 or Al-C-Ti (TiO_2) three-component systems. The reactive paths, formation mechanism of reinforcing phases, microstructural evolution, densification, and plastic processing have been investigated systematically.For Al-B-TiO_2 three-component system, the reduction reaction of TiO_2 by molten Al has been proved to be a stepwise process. Four oxygen-deficient titanium oxides could be formed, and Ti_2O_3 was a main intermediate phase. In addition to the oxygen-deficient titanium oxides, there also existed several transitional phases, such as AlB_2, γ-Al_2O_3, and Al_3Ti during the reactive sintering process of Al-B-TiO_2 powder mixtures. As the reinforcements in the composites, Al_2O_3 was formed by a series of aluminothermic reactions, while the formation of TiB_2 depended to a large extent on AlB_2 transitional phase. Small-sized TiO_2 powder promot … More ed the formation of the reinforcing phases at lower temperatures, and the resultant reinforcing particulates exhibited smaller sizes, compared to large-sized TiO_2 powder.With regard to Al-C-Ti mixed powder, concurrent with the generation of TiC particulates, Al_3Ti phase was generally formed during the reactive sintering. In order to avoid the occurrence of Al_3Ti phase, sintering at a higher temperature, displacement of Ti by TiO_2, and addition of excess amount of C have been proved to be effective methods.It was shown that porous sintered specimens could be densified to a high-density level by hot compression. Furthermore, sound composite sheet could be obtained by hot rolling in a temperature range of 350-450℃. Because of the existence of submicron particulates which were homogeneously dispersed in Al matrix, the composites exhibited good mechanical properties, especially in strength and Young's modulus. In comparison with conventional powder metallurgy and various casting techniques, the reactive sintering process has been shown to be a promising approach to fabricate aluminum matrix composites reinforced with fine ceramic particulates. Less