Mechanistic investigation of the field-activated combustion synthesis (FACS) of titanium aluminides

The reaction mechanism of the field-activated combustion synthesis (FACS) of the phase TI,AI from elemental powders is investigated. Intermediates of reaction leading to final product are identified by performing X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) of quenched samples obtained by turning off the applied field during wave propagation. The combustion reaction is preceded by the melting of aluminum which then spreads over the titanium particles. Hence, the liquid aluminum reacts with titanium giving rise to a layer of TiAl3 which grows around the original Ti particles until the aluminum disappears completely. Subsequently, the unreacted Ti interacts with TiAl3. The resulting grains consist of Ti cores surrounded by a layer of T3Al which in turn is surrounded by another layer of TiAl. This interaction further proceeds leading to a shrinkage of Ti cores, the gradual disappearance of the TiAl layer, and the simultaneous increase of the Ti3Al content. A single Ti3Al phase product is finally obtained. (C) 1999 Elsevier Science Ltd. All rights reserved.