Friction Stir Welding of Inconel-718 Alloy Using a Tungsten Carbide Tool

In this work, an attempt was made to join Inconel 718 by FSW using a tungsten carbide tool. The influence of major operating parameters such as rotational and traverse speed on the thermal history, axial force, mechanical and microstructural properties of welded samples was investigated. To obtain a sound weld joint, lower rotational speed (i.e., 300 rpm) and moderate traverse speed (i.e., 90 mm/min) are preferable. A sound weld joint experienced a joint efficiency of 100.2% and the impact toughness was 84.5%, of the base material. Grain refinement occurs both in the stir zone (SZ) and thermo-mechanical affected zone (TMAZ), with lower rotational speed and increasing traverse speed. The grain refinement leads to the improvement of mechanical properties such as tensile strength, impact toughness and Vickers hardness. XRD analysis revealed the existence of both tungsten and cobalt particles in the weld zone which confirmed the tool wear happened during the FSW. From FESEM and transmission electron microscopy (TEM) investigations, it was observed that the SZ of the sound weld sample revealed the presence of refined grain with secondary phases, which are most likely to be responsible for enhancing weld strength.