Strain ageing in γ(TiAl)-based titanium aluminides due to antisite atoms

The deformation behaviour of two-phase titanium aluminides was investigated in the intermediate temperature interval 450-750 K. The observed deformation characteristics include discontinuous yielding and negative strain rate sensitivity, which are indicative of the operation of the Portevin-LeChatelier effect. The pinning processes occurring at the dislocations and associated with these phenomena were studied by static strain ageing experiments. A wide range of alloy compositions and microstructures was investigated in order to identify the relevant defect species. Accordingly, dislocation pinning is characterized by a relatively small activation energy of Q(a)=0.7eV being not consistent with a conventional diffusion process. Furthermore, the strain ageing phenomena are most pronounced in Ti-rich alloys. This gives rise to the conclusion that antisite defects are involved in the pinning process. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.