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

Abstract The comprehensive kinetics of the exothermic TiAl 3 synthesis reaction, under the nominal formula Ti + 3Al → TiAl 3 , 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 TiAl 3 , the diffusion between Ti and Al through TiAl 3 -layer and the diffusion between TiAl and Al through TiAl 3 -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 TiAl 3 by scanning electron microscopy (SEM) and electron probe microscopic analysis (EPMA), which indicates TiAl is a transitional product during the process of TiAl 3 synthesis. Such a metallographic result is consistent with the thermokinetic interpretation.