Effects of deformation stress mode on twin activation of CP-Ti wire through cryogenic non-circular drawing sequence

A cryogenic-temperature–non-circular drawing sequence (CT-NCD) at 123 K was designed to investigate the effects of the deformation stress mode on the twin activation of a commercial pure titanium (CP-Ti) for manufacturing a high-strength CP-Ti wire. A cryogenic tensile test was conducted using a digital image correlation camera in a cryogenic chamber. The cryogenic-tensile strength of CP-Ti was improved by 58.5% and strain was improved by 52.1% when compared with the tensile-test results at room temperature. The CT-NCD was conducted in the cryogenic chamber and the results were compared with those of the room-temperature wire drawing (RT-WD). The numerical and experimental results confirmed that the CT-NCD sequence continued to produce faultless CP-Ti wires. The mechanical properties of the CT-NCD wire showed that the strength increased by 12.6% with comparable ductility, and micro-Vickers hardness increased by 17.4% when compared with that of the RT-WD. The twin map obtained through electron-backscattering diffraction showed that the twinning of the CT-NCD wire significantly increased when compared with that of the RT-WD due to temperature and process effects. From the numerical analysis results, the NCD sequence generated more tensile twin than WD owing to the deformation stress mode change by a die shape. It was concluded that the proposed CT-NCD sequence affects twin activation by deformation stress mode from the die design and temperature changes, compared to the conventional RT-WD, resulting in grain refinement and mechanical property enhancement. Based on the results, CT-NCD is considered useful for manufacturing the high-strength CP-Ti wire for industrial applications.