Microstructural Evolution and Grain Refinement in Gas Tungsten Constricted Arc (GTCA) Welds of Inconel 718 Alloy—Mechanism and Segregation Analysis

The magnetic arc constriction and current pulsing techniques were employed to control segregation of Nb and laves phase precipitation in the fusion zone of conventional gas tungsten arc (GTA) welded Inconel 718 alloy joints. In this paper, an emphasis was laid to understand the mechanism responsible for grain refinement in fusion zone microstructure and corresponding influence on laves phase evolution in interdendritic regions. The joints welded at an optimum level of heat input showed finer dendritic structure leading to the evolution of finer discrete laves phase in fusion zone. However, the arc constriction and current pulsing techniques were not effective at higher heat input levels. The welded joints were free from microfissuring in the heat affected zone (HAZ) though welded at high heat input, thus proving its advantages over the other variants of GTA welding process.