Slip and fatigue crack formation processes in an α/β titanium alloy in relation to crystallographic texture on different scales

The purpose of this experimental study is to investigate the micromechanical fatigue behavior, in terms of slip nature and preferential cracking sites, of a commercial α/β-forged Ti–6Al–4V alloy. Electron backscattering diffraction is extensively used to identify the deformation (prismatic, basal, pyramidal slip) and crack formation modes activated by fatigue at the surface of several hundred primary α nodules. Some fatal crack formation sites are also characterized. Cracking in basal planes is identified as the most critical damage mode leading to fracture. An explanation is proposed which involves the resolved shear stress, taking into account the Schmid factor and the normal stress in relation to the elastic anisotropy of the α-phase. Finally, the spatial distribution of the secondary cracks is analyzed according to the crystallographic textures (macrozones) present on a mesoscopic scale in the Ti–6Al–4V alloy.