Grain-boundary sliding in a TiAl alloy with fine-grained duplex microstructure during 750 °C creep

Constant-load creep experiments at a temperature of 750 °C and a nominal stress of 300 MPa were conducted on a fine-grained Ti–45Al–5Nb–0.2B–0.2C (in at.%) alloy with a duplex microstructure. Microstructures before and after creep (accumulated strain: 9.6%) were analyzed using scanning and transmission electron microscopy (SEM and TEM). TEM analysis after creep indicates that the individual microstructural constituents of the fine duplex microstructure, namely, the equiaxed γ and the lamellar α2/γ colonies, undergo varying degrees of deformation and develop various substructures. Lamellar grains deform by dislocation creep. They show clear evidence for dislocation and twin activity. In contrast, only few dislocations are found in the equiaxed grains. We show that the regions with small equiaxed γ grains, representing 65–75 vol.% of the microstructure, deform by grain-boundary sliding.