Microstructure and steady state creep in Ti-24Al-11Nb

Abstract

The steady state creep behaviour of the two-phase Ti₃Al-based alloy, Ti-24Al-11Nb, has been examined as a function of microstructure at temperatures ranging from 798 to 998 K and stress levels ranging from 30 to 400 MPa. Three microstructural conditions corresponding to 90% equiaxed α₂, 40% equiaxed α₂, and 100% lath α₂ structures have been studied. A low-stress Coble creep regime has been identified, with the lath α₂ structure showing the greates creep resistance in this regime. The lath α₂ structure is also stronger in the dislocation creep regime. The creep strength of this ordered alloy is shown to derive from frequency factors for diffusion, which are about two to three orders of magnitude lower than those for disordered alloys. Activation energies for creep in both the diffusional and dislocation creep domains are similar to values obtained in disordered alloys.