Strain ageing in α2(Ti3Al)- and γ(TiAl)-based titanium aluminides

Deformation of alpha(2)(Ti3Al)- and gamma(TiAl)-based TiAl between 450-850 K is characterized by negative strain-rate sensitivity and strain ageing effects. These phenomena are usually associated with dislocation locking according to the Portevin-LeChatelier effect. The pinning processes occurring at the dislocations and associated with these phenomena were studied by static strain ageing experiments involving a wide range of alloy compositions. The strain ageing phenomena are generally more significant for off-stoichiometric compositions, when compared with stoichiometric alpha(2) or gamma alloys. This gives rise to the speculation that antisite atoms are involved in dislocation locking. The investigation of the relevant pinning mechanism in terms of the defect processes involved is the subject matter of the present paper.