Effect of Oxygen Contents in Shielding Gas on GTAW Joints of Commercially Pure Titanium

This work investigates the impact of oxygen content in shielding gas on GTAW joints of commercially pure titanium. Commercially pure titanium GTAW welds exhibit unique color characteristics, with silver, straw, and white/gray indicating varying degrees of quality. The study finds that a 100% argon shielding gas results in silver-colored, acceptable welds. However, increasing the oxygen content of shielding gas leads to color changes, indicating oxidation and potential defects. Liquid penetrant testing confirmed that oxygen contents of 10 vol.% or higher resulted in cracks and reduced weld quality. Microstructure analysis reveals the thickening of surface oxide layers with increased oxygen content, while XRD analysis identified Ti6O and TiO2 oxide phases. Weld penetration remains consistent, but oxygen-rich environments lead to narrower melt pools and irregular bead shapes. Microstructural analysis shows the formation of beta-Ti phases and subgrains in the fusion zone, influenced by oxygen content. Hardness increases with higher oxygen content due to precipitation and subgrain formation. The average hardness of the fusion zone increased from 204 Hv under 100% Ar to 251, 278, and 384 Hv at 3 vol.%, 5 vol.%, and 10 vol.% oxygen, respectively. In contrast, the tensile strength progressively decreased from approximately 430 MPa to 420, 410, and 370 MPa, respectively, with reduced ductility at higher oxygen contents. These results demonstrate that oxygen content in the shielding gas significantly influences the microstructure and mechanical properties of commercially pure titanium GTAW joints, and maintaining oxygen content below 5% in the shielding gas during GTAW of pure titanium positively affects weld quality and mechanical performance.