Thermoanalytical and metallographical investigations on the synthesis of TiAl3 from elementary powders

The comprehensive kinetics of the exothermic TiAl3 synthesis reaction, under the nominal formula Ti + 3Al → TiAl3, was studied by applying Friedman method to non-isothermal DSC data of Ti–75 at.% Al powder compact. According to the characteristic of the dependence of the apparent activation energy (E) on conversion degree (α), three processes were identified with E of 109, 175 and 89 kJ mol−1 in sequence. By correlating the values of E to reported ones, these processes could be interpreted as the direct chemical reaction at the interface between Ti(s) and Al (l) to form TiAl3, the diffusion between Ti and Al through TiAl3-layer and the diffusion between TiAl and Al through TiAl3-layer. In order to verify these thermokinetic interpretations metallographically, a laser-igniting and self-quenching method was performed. In the laser-ignited and self-quenched Ti–75 at.% Al compact, there are three regions identified as reacted, transitional and unreacted regions, respectively, along the longitudinal direction. In the transitional region, TiAl-layer was identified between remained Ti core and the layer of the final product TiAl3 by scanning electron microscopy (SEM) and electron probe microscopic analysis (EPMA), which indicates TiAl is a transitional product during the process of TiAl3 synthesis. Such a metallographic result is consistent with the thermokinetic interpretation.