Deposit Formation Characteristics, Microstructure, and Mechanical Properties of the 304 Stainless Steel Fabricated by Activated Two-GTA-based Additive Manufacturing

To improve the deposition rate of conventional gas tungsten arc-based additive manufacturing (GTA-AM), an activating two-GTA additive manufacturing (AT-GTA-AM) was developed by using a two-GTA activated via mixing minor oxygen into the shielding gas of the forward welding torch. The effects of the deposition current through the electrodes, arc travel speed, and wire feeding speed on the deposit layer formation were investigated for a single-layer deposition of SUS 304 stainless steel. The impact of oxygen on the formation characteristics, microstructure, and mechanical properties is presented, and the mechanisms of the deposit formation are discussed. The results indicate that the AT-GTA-AM method achieves a significantly improved deposition rate (2.7 kg h^–1) for conventional GTA-AM and also realized at a relatively lower current (360 A) than reported in the literature (450 A), maintaining a stable process and structurally sound mechanical properties. Such an improvement is linked to the markedly reduced arc force (arc pressure and gas shear force) of the AT-GTA and improved wetting and spreading of the melt generated by the introduced oxygen element. In addition, the mixing of O₂ does not significantly influence the microstructure. It slightly reduces the ultimate tensile strength and elongation of the deposited wall, whereas it considerably increases the yield strength of the deposited metal.