Deformation microstructural evolution and strain hardening of differently oriented grains in twinning-induced plasticity β titanium alloy

The (332) < 113 > twinning structure evolution in nearly [122] and 1001] oriented grains was quantitatively examined in a polycrystalline Ti-15Mo alloy at various tensile strains. Twinning with a single variant, which obeyed Schmid's law, was induced in [122] grain after yielding. The area fraction of twins rapidly increased from 3% to W69% with strain from 0.02 to 0.15, and changed gradually to 81% at strains of up to 0.25. In [001] grain, twin formation violating Schmid's law with three variants was confirmed after the strain reached 0.01. Twins with an area fraction of 0.7% showed no significant change with further deformation. The contribution of deformation modes to the total tensile strain in [122] grain was dominated by twinning at strains of up to 0.15, and became dislocation slip with further deformation. In [001] grain, dislocation slip mainly contributed to the plastic deformation over the entire strain range. Dynamic microstructure refinement arising from twinning, namely the dynamic Hall-Petch effect, was the main strain hardening mechanism in [122] grain at strains of up to 0.15. However, strain hardening caused by twinning was negligible in [001] grain. The effects of local stress concentration and geometric constraint between neighboring grains on the deformation microstructural evolution and strain hardening behavior should also be considered. (C) 2016 Elsevier B.V. All rights reserved.