Samuel Hemery1,Cyril Lavogiez1,Patrick Villechaise1,Jean-Charles Stinville2,Fulin Wang3,Marie-Agathe Charpagne2,Meghan Emigh3,Tresa Pollock3,Valery Valle1
Institut Pprime1,University of Illinois at Urbana-Champaign2,University of California Santa Barbara3
Samuel Hemery1,Cyril Lavogiez1,Patrick Villechaise1,Jean-Charles Stinville2,Fulin Wang3,Marie-Agathe Charpagne2,Meghan Emigh3,Tresa Pollock3,Valery Valle1
Institut Pprime1,University of Illinois at Urbana-Champaign2,University of California Santa Barbara3
Titanium components employed in the aerospace industry generally experience fatigue loadings during in-service operation. Intense research efforts were put into the understanding of crack formation mechanisms to enable accurate prediction of the fatigue performance as well as microstructure optimization. However, literature review reveals an intricate situation owing to the competition between different mechanisms. In this presentation, a brief overview of microstructural features found at crack initiation sites in a variety of alloys with different microstructures and loading conditions will be reported first. Based on collected data, the occurrence of a single crack nucleation mechanism involving (0001) twist grain boundaries will be discussed and a criterion to identify candidates for crack initiation will be proposed. Details of the mechanism governing crack nucleation will then be described. Characteristics of these critical grain boundaries, including potential composition heterogeneities, were studied using TEM. In addition, their role in the early slip activity was investigated with a statistical significance using a combination of in situ tensile testing with high resolution DIC, EBSD and TEM. The transition from localized plasticity to crack formation at (0001) twist grain boundaries will finally be discussed in light of these results.