Multi-objective mathematical modeling and optimization of delta straight InterPulse-GTCAW parameters to predict and maximize performance of high temperature aerospace alloy sheets for structural applications

Abstract

Superalloy 718 is a high temperature nickel (Ni) based alloy, widely used in aeroengines due to its superior mechanical performance at high temperature. It is vulnerable to alloying segregation and Laves phase precipitation in fusion zone (FZ) which deteriorates the tensile properties of Superalloy 718 joints. Hence a newly emerged InterPulse GTCAW process featured by high frequency arc constriction was attempted to fabricate the joints of Superalloy 718. The main objective of this research work is mathematical modeling, prediction and optimization of delta straight GTCAW (DS-GTCAW) parameters for joining Superalloy 718 using response surface methodology (RSM). The process parameters were optimized for maximizing the tensile properties of joints and attain desired FZ microstructure. The tensile properties of Superalloy 718 joints were predicted from the mathematical relationships of DS-GTCAW parameters. The optical and scanning electron microscopy was used to characterize the microstructural features and tensile fracture surface morphology of high strength and low strength joints of Superalloy 718. The energy dispersive spectroscopy was used to characterize the alloying segregation of FZ. The mathematical equations were also formulated to predict the tensile properties of Superalloy 718 joints from secondary dendritic arm spacing (SDAS) of FZ microstructure. The joint developed using optimized DS-GTCAW parameters disclosed 99.20% joint efficiency which is enhanced by 30% than GTAW and comparable to electron beam welded (EBW) and laser beam welded (LBW) joints of Superalloy 718. It refers to the refining of dendritic FZ microstructure and Laves phase precipitation in finer form.