Microtexture effects on fatigue and dwell-fatigue lifetimes of Ti-6Al-4V

Abstract

The influence of microtexture on the fatigue and dwell-fatigue response of Ti-6Al-4V was investigated considering two regions of a part showing different degrees of microtexture. A high degree of microtexture resulted in a significant reduction in fatigue lifetime. No difference in crack initiation mechanism was observed, as main cracks formed along basal twist grain boundaries (BTGB) connected to the specimen surface. However, a key contribution of faster small crack growth in the strongly microtextured region is suggested. A 120 s dwell time resulted in a dwell-fatigue lifetime debit exceeding a factor of 10 in this region while it remained below a factor of 3 in the weakly microtextured region. In the dwell-sensitive region, internal nucleation of the main crack occurred at a BTGB and long range facetted growth was enabled by the adjacent microtextured region with a dominant [0001] orientation. In contrast, surface crack nucleation typical of fatigue failures dominated in the dwell-insensitive region. The limited growth of internal cracks suggests that the lack of path for rapid crack growth has a pivotal effect for the low dwell sensitivity. The competition between fatigue and dwell-fatigue damage highlights the importance of considering both in modeling approaches to obtain accurate lifetime predictions.