Study of the microstructure and mechanical properties of composites fabricated by the reaction method in an Al-TiO2-B2O3 system

This paper investigates the microstructure, mechanical properties and fracture mechanism of composites fabricated by the exothermic dispersion method in the Al-TiO2-B2O3 reaction system. When the B2O3/TiO2 mole ratio is zero, the reinforcements of the composites are composed of α-Al2O3 and Al3Ti. The α-Al2O3 particulates are segregated at matrix boundaries and cannot enter the aluminum matrix grains due to poor wetting with the matrix and the Al3Ti rods distribute uniformly throughout the matrix. The ultimate tensile strength and elongation of the composites at room temperature are 250.4 MPa and 4.0%, respectively. The fracture mechanism of the composite can be characterized by a crack nucleus initiating in the Al3Ti rod and then propagating to the interface because of the poor properties of Al3Ti. When the B2O3/TiO2 mole ratio reaches 1, the Al3Ti phase is almost eliminated, the ultimate tensile strength and elongation increase to 320.8 MPa and 10.6%, respectively, and the tensile fracture surface is composed of fine ductile dimples. When the test temperature is about 723 K and the B2O3/TiO2 mole ratio is 1, the elongation increases to 20.5% and the ultimate tensile strength decreases to 85.6 MPa.