PRIMARY CREEP IN A TI-25AL-11NB ALLOY

The primary creep strain has been evaluated at 923 K for three microst ructural conditions (fully equiaxed alpha(2), 40% equiaxed + lath alph a(2) and fully lath alpha(2)). 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 d iffusional creep regime. The magnitude of primary creep strain is seve ral times the elastic strain and unloading experiments show that it is fully recoverable. These results suggest that the mechanism of primar y creep in the diffusional creep regime is related to grain boundaries . In the dislocation creep regime, the magnitude of forward primary cr eep 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 o f primary creep strain.