Primary creep in a Ti-25Al-11Nb alloy

The primary creep strain has been evaluated at 923 K for three microstructural conditions (fully equiaxed α2, 40% equiaxed + lath α2 and fully lath α2). The results show that the primary creep strain depends both on the microstructure and the applied stress. The primary creep strain varies linearly with the applied stress in the diffusional creep regime. The magnitude of primary creep strain is several times the elastic strain and unloading experiments show that it is fully recoverable. These results suggest that the mechanism of primary creep in the diffusional creep regime is related to grain boundaries. In the dislocation creep regime, the magnitude of forward primary creep strain is much larger than the anelastic strain. The mechanism of primary creep is discussed in terms of various models. It is suggested that interfaces play an important role in determining the magnitude of primary creep strain.