Mechanistic understanding of creep in gamma-base titanium aluminide alloys

The paper describes an experimental study of creep processes in two-phase titanium aluminide alloys. The investigations involve long-term creep test at relatively low stresses and temperatures. These test conditions lead to very low strain rates, which are characteristic of the intended service conditions. The creep tests were coupled with detailed electron microscope observations involving high-resolution imaging techniques and in situ heating studies. Long-term creep leads to spheroidization and coarsening of the lamellar morphology, which involve phase transformations and recrystallization. Climb velocities were analyzed in terms of the critical vacancy supersaturation necessary for the operation of diffusion assisted dislocation climb sources. The mechanisms are closely related to the atomic structure of the interfaces and are probably driven by a non-equilibrium phase composition.