Tailoring the grain and microstructure of 316L stainless steel through wire-tungsten indirect arc directed energy deposition

Achieving an additive manufacturing (AM) process with a high deposition efficiency and excellent mechanical properties has long been an urgent goal. A wire-tungsten indirect arc directed energy deposition (DED-WTIA) technique that uses a tungsten electrode and filler wire as electrodes, whereas the workpiece is non-conductive, was adopted for the AM of 316L stainless steel. At a low welding current, a unique grain morphology was obtained. The formation mechanisms of this morphology were revealed by analyzing the arc characteristics and droplet transition behaviors. A fine microstructure consisting of γ-austenite dendrites and residual δ-ferrite was achieved under various weld current conditions, with the average dendrite width consistently ranging from 8 to 10 µm. Furthermore, high-speed imaging was employed to capture the droplet transition behavior and arc morphology at different weld currents. As the current increased from 80 to 200 A, the droplet transition mode changed from globular to spray transfer, significantly reducing the droplet size and resulting in a dramatic increase in the transition frequency. The heating effect of the arc was also observably improved, with the heating width on the substrate increasing from 2.6 to 11.4 mm, and the fusion ratio of the weld seam increasing from 3.4% to 30.0%.