Effects of microstructure on short crack growth behavior of Ti–6Al–2Sn–4Zr–2Mo–0.1Si alloy

Crack initiation and short crack behavior of Ti–6Al–2Sn–4Zr–2Mo–0.1Si (Ti6242) with fine and coarse lamellar microstructure were characterized. The fine microstructure showed a good crack initiation resistance compared with the coarse microstructure while the latter had better resistance to crack propagation than the former. Material microstructure influenced the degree of oscillation in crack growth rates during early crack growth stage and the surface crack length at which the transition from Stage I to Stage II occurred. No difference in short crack growth behavior between the two microstructures was observed. In the fine microstructure, the behavior of short and long crack growth was similar. However, in the coarse microstructure, the short crack growth rate was almost one order magnitude faster than the long crack growth rate at a given stress intensity factor range. Overall, the long crack with the coarse microstructure was more fatigue resistant than the three others, which were all similar. This resulted from the fact that the long crack growth is significantly affected by the anisotropic microstructure in the coarse case, i.e. variations in colony size and orientation between neighboring colonies.