Formation of composites fabricated by exothermic dispersion reaction in Al-TiO 2-B 2O 3 system

Abstract

The formation of aluminum matrix composites fabricated by exothermic dispersion reaction in Al-TiO 2-B 2O 3 system was investigated. The thermal analysis results show that the reactions are spontaneous and exothermic. The Gibbs free energy of α-Al 2O 3 is the lowest among all the combustion products, followed by TiB 2 and Al 3Ti. It is noted that when the B 2O 3/TiO 2 mole ratio is below 1, the reaction products are composed of particle-like α-Al 2O 3, TiB 2 and rod-like Al 3Ti. The α-Al 2O 3 crystallites, resulting from the reaction between Al and TiO 2 or B 2O 3, are segregated at the grain boundaries due to a lower wettability with the matrix. SEM micrographs show that rod-like Al 3Ti phase distributes uniformly in the matrix. When the B 2O 3/TiO 2 mole ratio is around 1, the Al 3Ti phase almost disappears in the composites, and the distribution of α-Al 2O 3, particulates is improved evidently.