Uncovering the link between twin-twin interactions and damage nucleation in an (α+β) Ti alloy

Abstract

Recently, a (α+β) Ti alloy was developed with an outstanding combination of both high strength and high ductility; however, the plasticity micromechanisms that lead to damage nucleation for this alloy had not yet been investigated in detail. In this work, post-mortem analysis and an in-situ SEM-EBSD tensile experiment were conducted to determine where damage was nucleating most frequently in the microstructure, and what deformation modes were associated with damage nucleation. Damage within primary α grains was found to be the most common, with most of these damage incidents occurring along {10̅12} twin-twin boundaries with a ~60° misorientation. The {10̅12} twinning mode is only activated in the localized neck, and twin activation is strongly dependent on initial crystallographic texture. The twinned domains are rotated such that prismatic slip is easier to activate, but prismatic slip transfer is unlikely across ~60° twin-twin boundaries due to geometric incompatibilities. The in-situ test revealed that a crack formed along a ~60° twin-twin boundary where slip was blocked. These findings provide new insights into how twin-twin interactions in Ti alloys can lead to damage nucleation and impact overall ductility.