Creep behaviour of a cast TiAl-based alloy for industrial applications

Abstract The creep behaviour of a cast TiAl-based alloy with nominal chemical composition Ti–46Al–2W–0.5Si (at.%) was investigated. Constant load tensile creep tests were performed in the temperature range 973–1073 K and at applied stresses ranging from 200 to 390 MPa. The minimum creep rate is found to depend strongly on the applied stress and temperature. The power law stress exponent n is determined to be 7.3 and true activation energy for creep Q is calculated to be 405 kJ/mol. The initial microstructure of the alloy is unstable during creep exposure. The transformation of the α 2 (Ti 3 Al)-phase to the γ(TiAl)-phase, needle-like B2 particles and fine Ti 5 Si 3 precipitates and particle coarsening are observed. Ordinary dislocations in the γ-matrix dominate the deformation microstructures at creep strains lower than 1.5%. The dislocations are elongated in the screw orientation and form local cusps, which are frequently associated with the jogs on the screw segments of dislocations. Fine B2 and Ti 5 Si 3 precipitates act as effective obstacles to dislocation motion. The kinetics of the creep deformation within the studied temperature range and applied stresses is proposed to be controlled by non-conservative motion of dislocations.