An innovative multi-ring inert gas shielding system was proposed to achieve oxygen isolation for the laser direct energy deposition (LDED) of Ti-6Al-4V alloy. Firstly, a quantitative correlation was established between the diameter of the low oxygen area on the substrate and key parameters of the multi-ring inert gas shielding system, including the argon gas convergence angle and the ring gap dimensions, based on detailed flow field analysis. Visualization results obtained via the schlieren method basically matched the predicted gas flow field. Secondly, the key parameter combination was optimally configured and a uniform low oxygen area (the oxygen concentration < 50 ppm, diameter 44.66 mm) was achieved at an argon gas flow rate of 45 L/min. The deposited Ti-6Al-4V alloy layer and block displayed a silver-white or light-yellow coloration, suggesting minimized oxidation during the LDED process. Finally, the multi-ring inert gas shielding system was applied to fabricate Ti-6Al-4V components in the oxygen-rich environment. It was found that the powder splashing and smoke were effectively suppressed in the local inert atmosphere, and the oxygen inhibition rate of more than 23.8% was achieved. In addition, tensile strength of 1043 ± 18 MPa and yield strength of 951 ± 20 MPa were obtained for the protective formed Ti-6Al-4V component, with an improvement of 16.6% and 15.3% respectively, compared to the forged parts. • A multi-ring gas shielding system enables large-area titanium LDED in open air. • An optimized 3-ring design creates a uniform low oxygen zone over 44 mm. • Two Ti6Al4V components was successfully fabricated with silver-white surfaces. • Deposited parts exhibit 16.6% higher tensile strength than forged standards.
Gong et al. (Sun,) studied this question.