Influence of electric current on microstructure evolution in Ti/Al and Ti/TiAl₃ during spark plasma sintering

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.