Transient creep of Ti–Al–Nb alloys

The creep tests of seven Ti–Al–Nb alloys, all of which had a microstructure of B2+α2, B2+α2+O, or B2+O, were carried out at 650∼750 °C/310 MPa. The activation energy for transient creep was calculated to be 333–439 kJ mol−1, which was approximate to that for the steady-state creep (327–416 kJ mol−1). The values of activation energy indicate that the transient creep, as well as the steady-state creep, was controlled by high-temperature dislocation climb. The relation between transient creep time (ttr) and steady-state creep rate (ε̇s) obeyed the equation ttr=C/ε̇s, with C=5.00×10−3. The transient creep strain increased with increasing volume fraction of B2 phase, and also increased with decreasing creep temperature; these findings are considered to be due to both the low work-hardening rate of B2 phase, and a stress-accelerated phase transformation from B2 to O or α2.