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 [001] 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 69% 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.