Grain refinement in a metastable beta Ti alloy deformed to large strains at high strain rates

Abstract

Shear punching to large plastic strains up to 40 was conducted on a metastable β Ti alloy at various speeds, creating severe plastic deformation at high shear rates (γ˙) up to 200 s−1. Grain refinement in the resulting shear bands (SBs), which experienced even faster deformation due to strain localisation, was studied using extensive TEM. Significant grain refinement occurred at γ˙ < 40 s−1, producing β grains of ∼5–10 nm, considerably smaller than those obtained by high pressure torsion (HPT) to a much higher strain of 240 at a slow shear rate of 0.5 s−1. The applied shear strain rate of 2 s−1 was found to be an optimum for attaining a pure nano-β grain structure thanks to maximum dislocati..