Microstructural evolution of equal channel angular drawn purity titanium at room temperature

Abstract

Thin commercial-purity titanium (CP–Ti) wire was successfully acquired by equal channel angular drawing (ECAD) at room temperature with route Bc using a 90° die at a relatively high drawing speed of 10 mm s−1. The as-drawn CP–Ti wires were of good quality free of cracks and segmentation on their surface. The grain size of CP–Ti was reduced from ∼32 μm for the as-annealed wire to ∼700 nm for 12-passes equal channel angular drawn wire. The grain experienced transition from microband to thin lath and to equiaxed subgrains with the increment in drawing passes. Face-centered cubic (FCC) phase was triggered obviously to accommodate the large shear strain induced by ECAD at the drawing rate of 20 mms−1. The thickness of the FCC phase increased with an increase in drawing passes, and no equiaxed subgrains were formed in CP–Ti. Accordingly, the drawing speed significantly affects the deformation mode and microstructural evolution of CP–Ti during ECAD. A lower drawing speed provides a longer time for the structure recovery, thus resulting in the occurrence of dynamic recovery when ECAD was performed at room temperature. Additionally, {101¯2} tension twinning and {112¯2} compression twinning occurred simultaneously to accommodate ECAD shear deformation. The success in processing CP–Ti rods at room temperature through multiple passes of ECAD provides a new perspective to efficiently fabricate ultrafine grained small-sized materials continuously.