Study on formability of 9%Ni low-temperature steel fabricated by plasma arc powder directed energy deposition

Plasma arc powder directed energy deposition (DED-P), is the technique, in depositing the coaxially delivered powder melted by the plasma arc layer by layer to form 3D components. Due to the dispersed energy distribution and high arc pressure of the plasma arc, compared with laser coaxial powder feeding, the molten pool exhibits lower stability and quality. Therefore, clarifying the complex coupling relationships among the plasma arc, powder, and molten pool is of great significance for process parameter selection and fabrication quality control. Therefore, this study systematically investigates the effects of deposition speed, current, plasma gas flow rate, and torch height on single deposited bead morphology through deposition experiments, molten pool dynamic simulations, and high-speed infrared imaging. The result shows that, a well-formed single deposited bead can be obtained through lower deposition speed. Due to the heat input remains relatively stable, and the molten metal can sufficiently spread under the combined effects of surface tension and the gravity, resulting in the uniform and stable single deposited bead. In contrast, higher deposition speed and welding current tend to induce humping defects. This is attributed to the significantly enhanced arc force and heat input, which intensify molten pool convection and the instability; however, insufficient solidification time and the mismatch between material supply and molten pool spreading lead to local accumulation of molten metal at the rear of the molten pool, thereby forming humping defects. The above results will provide a reference for understanding the forming process of DED.