The effect of processing variables on the structure and chemistry of Ti-aluminide based LMCS

The effect of processing variables on the growth of a titanium alummide layer produced from elemental titanium and aluminum foils was examined, with the intention of yielding a titanium-titanium aluminide composite structure. To produce the intermetallic phase in situ, two processing techniques were employed, diffusion bonding and combustion synthesis. Microstructural examination of the titanium alummide layer revealed striking similarities in the resulting morphology yielded by both processing techniques, in particular for those samples diffusion annealed at lower temperatures (615 degreesC and below) and those reacted by combustion synthesis. In both cases, an exothermic chemical reaction was responsible for alummide formation in specimens, and in those samples processed by diffusion bonding, this reaction was observed to be rate controlled by a diffusion mechanism. Chemical analysis of the product alummide showed the layers to be composed completely of a single phase, TiAl3, which is believed to be the result of thermodynamic stability of this phase relative to other stable equilibrium phases in the titanium aluminum system. The results of these experiments are discussed with a view of utilizing these processes to optimize the mechanical behavior of titanium alummide by incorporating it into a laminated metal composite. (C) 2002 Elsevier Science B.V. All rights reserved.