Abstract
The synthesis of γ-TiAl from elemental metals via solid-state reactive diffusion processing routes involves multiple reaction steps with the formation of various intermediate intermetallic compounds, starting with TiAl3 because this phase is favored kinetically. To understand the processes by which the TiAl3 intermediate is eliminated during synthesis of γ-TiAl alloy via spark plasma sintering (SPS), the reaction between Ti and TiAl3 during SPS was studied with emphasis on the effects of the applied electric current and starting TiAl3 microstructure on the reaction kinetics and the underlying diffusion mechanisms. The intermediate intermetallic phases Ti3Al, TiAl and TiAl2 were formed between the Ti and TiAl3 upon SPS processing at 900 °C. The applied electric current did not alter the character of the phases formation in the Ti/TiAl3 system, but thermodynamic calculations suggest that the activation energy for the nucleation of TiAl2 is reduced significantly with an electric current flowing. Moreover, the kinetics of the reactions between Ti and TiAl3 were enhanced when the starting TiAl3 microstructure was refined. The electric field also had a more significant influence on the grain growth kinetics for TiAl2 and TiAl in powder blend compacts with refined microstructures.
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