A TEM study of deformation processes and microstructural changes during long-term tension creep of a two-phase γ-titanium aluminide alloy

Long-term tension creep tests were performed on a Ti-48 at.% Al-2 at.% Cr alloy in order to assess the material behaviour under the intended service conditions for structural parts in turbine engines. Deformation processes and microstructural changes were investigated by TEM on a specimen loaded to 140 MPa for 5988 h at 700 degrees C. At lamellar boundaries the emission of interfacial dislocations was observed and was thought to contribute significantly to the high primary creep rate of the material. Under the applied creep conditions gliding dislocations apparently become locked by heterogeneous formation of precipitates along their cores. Also substantial microstructural changes were observed in lamellar colonies. These are the dissolution of at lamellae and the formation of ledges at lamellar interfaces with heights up to 200 nm. By ledge formation and growth the interfaces migrate, which contributes to creep deformation. At ledges recrystallized grains were also formed contributing to the degradation of the lamellar microstructure. (C) 1999 Elsevier Science Ltd. All rights reserved.