Effect of delta current on the microstructure and tensile properties of gas tungsten constricted arc welded Inconel 718 alloy joints

Abstract

Inconel 718 is a nickel-based superalloy which is of potential interest in high temperature applications in rocket and gas turbines. This alloy is mostly joined by Gas Tungsten Arc Welding (GTAW) process for clean and precise welds and it is economical and shop friendly. However, due to the high heat input associated with this process, the joints are more prone for metallurgical problems such as coarse dendritic structure and segregation in weld metal region and liquation cracking in heat affected zone (HAZ) which significantly reduces the mechanical properties of the welded joints. To overcome these shortcomings, a recently developed Gas Tungsten Constricted Arc Welding (GTCAW) process is used for joining Inconel 718 alloy. It is the advanced variant of GTAW process with magnetic arc constriction achieved by introducing high frequency pulsing Current (known as Delta Current). Delta Current pulsing at a very high frequency is controlling factor for the rise and fall of magnetic arc constriction during welding. The main objective of this investigation is to make the potential use of Magnetic Arc Constriction to reduce the heat input for minimizing metallurgical problems and enhancing the mechanical properties of the joints. To achieve this, main effect of Delta Current on tensile properties and microstructural characteristics of Inconel 718 alloy is investigated.