Microstructural evolution of reactive-sintered aluminum matrix composites

Abstract

Aluminum matrix composites reinforced with TiB 2 and Al 2O 3 particulates were synthesized via reactive sintering of Al–B–TiO 2 three-component powder mixtures. The effects of powder particle size and reactive sintering temperature on formation of reinforcing phases and microstructural evolution have been investigated. The reduction reaction of TiO 2 by molten Al has been proved to be a stepwise process. Four oxygen deficient titanium oxides can 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. As the reinforcements in the composites, Al 2O 3 is formed by a series of aluminothermic reactions, while the formation of TiB 2 depends on AlB 2 transitional phase. AlB 2 was gradually transformed to a mixed diboride (Al,Ti)B 2, and subsequently to TiB 2, through displacement of Al in the metallic sublattice of AlB 2 by Ti atoms. Small-sized TiO 2 powder promoted the formation of the reinforcing phases at lower temperatures, and the resultant reinforcing particulates exhibited smaller sizes.