Reaction pathways, activation energies and mechanical properties of hybrid composites synthesized in-situ from Al–TiO2–C powder mixtures

In-situ aluminum matrix composites were fabricated from Al–TiO2–graphitic C powder mixtures using exothermic dispersion method. The effects of C/TiO2 molar ratio on the reaction processes, activation energies and mechanical properties of the resulting materials were investigated. When the C/TiO2 molar ratio is 0, Al reacts with TiO2 to produce fine α-Al2O3 particles and Ti, which then reacts with Al to form large rod-like Al3Ti phase. By adding graphite C into the Al–TiO2 system, the activation energy of the first reactive step increases; in addition, the resultant Ti preferentially reacts with C to form hard TiC particles. When the C/TiO2 molar ratio increases to 1.0, the Al3Ti phase disappears and the reinforcements consist of nano-sized α-Al2O3 and TiC phases. The tensile strength of the composites increases from 239.2 MPa to 351.8 MPa and the elongation increases from 4.1% to 5.6%, suggesting a marked increase in damage tolerance (i.e., toughness).