Evaluation of the microstructure of in-situ reaction processed Al3Ti-Al2O3-Al composite

1. Differential thermal analysis (DTA) of squeeze-cast TiOz/Al bulk indicates that an exothermic reaction occurs after the aluminium melts. A high temperature combustion synthesis process was achieved to produce a fully dense Al3Ti + (X-Al2O3+ Al in situ composite. 2. Very fine-scale dispersion of the Al3Ti and (X-Al2O3 reinforcing phases, ranging from 0.4 to l.Ojim, was obtained in the Al matrix. The Al3Ti phase, some containing Al2Ti precipitates, form in the shape of block and whisker. The nanometer scale U-Al2O3 particles are found near the Al3Ti phase and in the Al matrix, and, occasionally, within the Al3Ti phase. 3. Analysis of the microstructural evolution indicates that the in situ processing involves two steps: (1) a reaction process between the molten aluminium and TiO2 to produce alumina particulates and liquid Ti. (2) a subsequent solidification process of remained Al and Ti displaced from the reaction with decreasing temperature to produce Al + Al3Ti blocks and then the smaller Al3Ti precipitates form as the solidcools.