Effect of Delta Straight and Delta Pulsed arc Modes on Weld Bead Geometry, Microstructure and Tensile Properties of InterPulsed GTCA-Welded Inconel 718 Alloy Joints for Aerospace and Nuclear Applications

In this investigation, InterPulsed Gas Tungsten Constricted Arc Welding (IP-GTCAW) process was employed to minimize the Nb segregation and Laves phase precipitation in Inconel 718 (IN-718) alloy welds. Thin sheets of IN-718 alloy (2 mm thick) were joined in 980 °C solution annealed condition by two different modes known as delta straight (DS-GTCAW) and delta pulsed (DP-GTCAW) arc mode of IP-GTCAW process. The effect of delta straight and delta pulsed arc modes on weld bead geometry, microstructural features and tensile properties of IN-718 alloy joints was studied and compared. Results showed that DS-GTCAW joints exhibit superior tensile properties compared to DP-GTCAW joints due to the microstructural refinement and finer discrete Laves phase precipitation in fusion zone (FZ). The superior tensile properties of DS-GTCAW joints are mainly attributed to the optimum level of thermal oscillation in weld pool caused by delta current pulsation which offers the potential benefits of current pulsation and arc constriction in grain refinement. The lower tensile properties of DP-GTCAW joints are mainly due to the excessive thermal oscillation in weld pool caused by the combined effect of welding current and delta current pulsation which does not provide the potential benefits of current pulsation and arc constriction in grain refinement.