Crack initiation and propagation in Ti-6Al-4V-0.55Fe alloy subjected to the low-cycle dwell-fatigue

This paper investigated the crack initiation and propagation behaviour of Ti-6Al-4V-0.55Fe alloy under the low-cycle dwell-fatigue. It found that cracks were preferred to initiate at the α/β-phase boundaries, the α/α-phase boundaries, and the twinning boundaries within the α-phase. Twinning played a key role in the crack initiation, for the reason that it changed the phase orientation on its sides. Besides, grain orientation was another important factor in the crack nucleation. The soft/hard grain boundaries may become the crack nucleation sites due to the dislocation pile-up. In addition, as the dwell time increased, the fraction of the high Schmid factor of prismatic slip was increasing, which resulted in more cracks. Furthermore, the fracture mode of the alloy was intergranular fracture with microporous aggregation.