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

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 alpha(2)(Ti3Al)-phase to the gamma(TiAl)-phase, needle-like B2 particles and fine Ti5Si3 precipitates and particle coarsening are observed. Ordinary dislocations in the gamma-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 Ti5Si3 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. (c) 2005 Elsevier Ltd. All rights reserved.