Understanding the role of local texture variation on slip activity in a two-phase titanium alloy

Abstract

During plastic deformation of engineering alloys with a hcp crystal structure, slip systems with different critical resolved shear stresses can be activated. In the case of two-phase titanium alloys such as Ti-6Al-4V, it is well established that various a→ and c→+a→ type slip systems can be activated in the α-phase, which dominates this alloy. However, their relative likelihood is less well established particularly when comparing prismatic a→ and basal a→ slip which are known to have similar critical resolved shear stress values. By combining EBSD-based grain orientation mapping and high-resolution digital image correlation, grain specific shear strain mapping and Burgers vector direction analysis was carried out after small levels of plasticity in two differently microtextured Ti-6Al-4V samples. This enabled the different types of strain heterogeneity and strain patterns to be linked to the underlying microstructure and microtexture. The detailed analysis shows that the dominance of a particular a→ type slip mode greatly varies with the local texture and that shear strain patterns extend across many grains when soft macrozones (clusters of similarly orientated grains) are present. The work highlights that the relative displacement ratio analysis significantly improves slip trace analysis in hcp crystals by reducing the cases of ambiguous solutions and that grain neighbourhood can have a greater impact on slip system activation than Schmid factor.